Tag Archives: mosquito

A lab experiment shows that we could engineer malaria-carrying mosquitoes to kill themselves off

A new paper showcases how genetic engineering can be used to cause populations of malaria-spreading mosquitoes to self-destroy.

Image credits Egor Kamelev.

An international research effort has shown, in the context of a lab experiment, that male mosquitoes engineered to carry a certain strand of DNA can rapidly destroy entire groups of these blood-sucking insects. The main importance of this experiment is that it showcases that gene-drive technology can be used even in harsh environmental conditions, such as those in sub-Saharan Africa.

This “gene drive” sequence is essentially a damaging mutation that could prove to be a powerful tool against the carriers of malaria.

Drastic measures

“Our study is the first [that] could show that gene-drive technology works under ecologically challenging conditions,” says Ruth Muller, an entomologist who led the research at PoloGGB, a high-security lab in Terni, Italy. “This is the big breakthrough that we made with our study.”

While this experiment has been a success, that doesn’t mean it’s going to be used any time soon. For that to happen, the authors first need to prove that their edited mosquitoes can work in practice — i.e. that they’re safe to release into the wild. Not only that but local governments and residents will have to give their approval before any of the mosquitoes can be released.

Still, with that being said, malaria remains one of the most concerning diseases on Earth. It infects an estimated 200 million people every year, with an estimated annual death toll of around 400,000. This is despite decades of coordinated effort to contain it.

So the authors decided to use the CRISPR gene-editing technique to make mosquitoes, the carriers of the malaria parasite, to self-destroy. They worked with the Anopheles gambiae species, which is native to sub-Saharan Africa. The gene they modified is known as “doublesex”, and is normally carried by healthy females. The modified variant, however, deforms their mouths and reproductive organs, meaning they can’t bite (and thus spread the parasite) nor lay eggs. This is combined with a gene drive, “effectively a selfish type of genetic element that spreads itself in the mosquito population,” says Tony Nolan of the Liverpool School of Tropical Medicine, who helped develop and test the mosquitoes.

Due to the risks involved in releasing these insects into real ecosystems, the experiments were carried out in small cages in a high-security basement lab in London. The modified mosquitoes showed that they can destroy populations of the unmodified insects here.

In order to test them under more natural conditions, however, the team also built a special high-security lab in Italy, specifically designed to keep the mosquitoes in. Here, dozens of gene-edited mosquitoes were released into very large cages containing hundreds of natural mosquitoes. Temperature, humidity, and the timing of sunrise and sunset mimicked the environment in sub-Saharan Africa. In less than a year, the authors report, the population of un-altered mosquitoes was all but wiped out.

Both of these steps were carried out far from the insects’ natural range as extra insurance in case any of them got out.

Whether such an approach will ever actually be used in real-life settings is still a matter of much debate. Even so, the study showcases one possible approach and strongly suggests that it would also function in the wild. It’s also a testament to how far gene-editing technology has come, that we could potentially have one of the most threatening (to us) species right now effectively destroy itself.

The paper “Gene-drive suppression of mosquito populations in large cages as a bridge between lab and field” has been published in the journal Nature Communications.

Scientists cut dengue fever cases by 77% using bacteria-infected mosquitoes

The target for elimination: Aedes albopictus. Image credits: Centers for Disease Control and Prevention’s Public Health Image Library.

Researchers affiliated with the World Mosquito Program, a non-profit concerned with protecting communities across the world from mosquito-borne diseases, just reported that its most recent trial meant to cull dengue in Indonesia was a stunning success. After releasing treated mosquitoes that were infected with a bacteria that makes them sterile, over the course of three years the number of dengue cases plummeted by nearly 77% while the number of dengue hospitalizations dropped by 86%.

The Wolbachia method

Dengue is a brutal mosquito-borne disease that causes flu-like symptoms but can be lethal and kill up to 20% of those with severe dengue. In the last five decades, dengue has gone from being present in a handful of countries to being endemic in 128 countries, where about four billion people live. In this timeframe, the number of dengue cases has increased 30-fold. As a result, the World Health Organization (WHO) listed dengue as one of the top global health threats in 2019 alongside Ebola, global flu pandemic, HIV, antimicrobial resistance and many others.

There is no specific treatment for dengue fever. For severe dengue, medical care by physicians and nurses experienced with the effects and progression of the disease can save lives – decreasing mortality rates from more than 20% to less than 1%. Maintenance of the patient’s body fluid volume is particularly critical to severe dengue care.

Dengue is transmitted by Aedes aegypti mosquitoes, which are responsible for a number of other illnesses including Zika and chikungunya. It is difficult to control or eliminate Ae. aegypti mosquitoes because they are highly resilient and can rapidly bounce back to initial numbers after disturbances such as droughts or human interventions. Their eggs can withstand desiccation (drying) and survive without water for several months on the inner walls of containers. But they may have finally met their match — the Wolbachia method.

Only female mosquitoes bite humans, which means that only females can transmit viruses. When mosquitoes are infected with the Wolbachia bacterium — a microbe present in at least 60% of all insects but rarely found in mosquitoes — two things happen. For starters, it makes most male mosquitoes sterile. Secondly, the bacteria are transmitted to offspring only by females.

Once a mosquito is infected with the bacterium, it makes it harder for viruses such as dengue to reproduce inside the insects, making the transmission from person to person far less likely. Because the effect of Wolbachia infection on insect reproduction favors the survival of Wolbachia-infected females over uninfected females, Wolbachia can rapidly spread through an insect population.

Wolbachia is harmless to humans. The benefits are that this is a non-chemical approach and that other insects and mosquitoes are not harmed.

Manipulating mosquitoes to stop spreading dengue with some help from bacteria

In 2017, researchers with the World Mosquito Program partnered with the Tahija Foundation and Gadjah Mada University and released Wolbachia mosquitoes within a 26km2 area of Yogyakarta City, Indonesia. The site was subdivided into 24 clusters, 12 of which were randomly selected to house Wolbachia mosquitoes, while the other dozen clusters were left untreated to act as a control.

Now, the team has reported the results of the trial in the New England Journal of Medicine, showing that Wolbachia deployments reduced dengue incidence by 77% and dengue hospitalisations by 86%.

Over the course of the trial, 318 dengue cases were detected in the untreated areas and only 67 in the Wolbachia-treated areas. There were only 13 hospitalizations for dengue in the Wolbachia-treated area compared to 102 in the untreated area. 

According to the researchers, once Wolbachia is established, it remains at a very high level in the mosquito population. The release of the Wolbachia mosquitoes was done transparently with the support of the local population.

Households voluntarily hosted these mosquito release containers, to which Wolbachia-carrying mosquito eggs, water and fish food were added once every two weeks, for 4-6 months. Adult Wolbachia-carrying mosquitoes emerged from the containers, then bred with wild-type Ae. aegypti mosquitoes until almost all Ae. aegypti in the intervention areas carried Wolbachia.

“In Yogyakarta, everybody knows somebody who has been impacted by dengue. Dengue is present in all provinces of Indonesia and is endemic in many large cities and small towns. The results of the RCT is welcome news for the people of Yogyakarta and a major breakthrough for the World Mosquito Program’s ambition to protect the wider Indonesian population,” reads a statement by the World Mosquito Program.

These results are consistent with those from other trials performed in Australia and Brazil, giving confidence that the reduction in dengue incidence can be replicated using the Wolbachia method in other parts of the globe. However, this needs to be thoroughly tested since differences in the circulating dengue serotypes can influence the results of the intervention.

Sterilised insects could help control mosquito-borne diseases

A form of tiger mosquito birth control and drones may help stem the spread of some tropical diseases. Image credit – James Gathany/CDC, public domain.

The bite of the Asian tiger mosquito may be little more than a pin-prick, but it leads to tens of thousands of deaths globally each year. 

The tiny aggressive insect, named for its striped appearance, carries a range of unpleasant viruses that cause diseases including yellow fever, dengue fever, Chikungunya, Zika and Japanese encephalitis. While these are seen largely as tropical diseases, the spread of mosquitoes that carry them has raised fears the viruses could also become more common in Europe.

The European Centres for Disease Control (ECDC) predicted ten years ago that tiger mosquitoes would spread throughout Europe and climate change is now threatening to make their spread even more likely. ‘Even the southern part of Sweden is potentially suitable climatically for this mosquito, though it has not arrived there yet,’ said Professor Jan Semenza, who leads an ECDC section which assesses infectious disease threats. 

The stripy pest, which is also known as Aedes albopictus, is originally from Southeast Asia, but arrived in Albania in the 1970s before reaching Italy in the 1990s. It initially colonised the Mediterranean coast, then steadily expanded northward, and is now found across much of France, Greece, Bosnia, parts of Spain, southern Portugal, and Germany. It has even been found in greenhouses in the Netherlands. During the summer, the mosquitoes have now become a nuisance in some places.

But with the mosquitoes can come disease. So far outbreaks have been relatively contained and in low numbers, but there have been cases of dengue in Croatia, France and Spain. In Italy, hundreds of people fell ill from Chikungunya in 2017. Two cases of locally caught Zika occurred in the south of France in 2019.

The diseases can be carried to Europe by people infected with the virus traveling from countries in South America and Asia where they are endemic. Brazil, for example, has been a hotspot this year for dengue fever. If these people are bitten by a tiger mosquito in Europe, the insect can then transmit the virus to other people it bites.

‘We have seen an increase in vector capacity due to climate change,’ warns Prof. Semenza, with warmer temperatures allowing the biting insects to survive over winter. ‘Dengue has a huge disease burden worldwide. It can morph into a life-threatening condition, so we are concerned about it moving into Europe.’

Dengue was endemic in Greece in the early 20th century but was eliminated. ‘We don’t want a recurrent of this type of disease in Europe,’ added Prof. Semenza. 

But rising numbers of mosquitoes capable of carrying disease makes it more likely that these viruses could become established in Europe once again. Another disease-carrying insect – Aedes aegypti, also known as the yellow fever mosquito – is also threatening a return to Europe after it was eradicated there in the 20th century. Originally from Africa, it is present today near the Black Sea, on the Portuguese island of Madeira and north-eastern Turkey.

But with many insecticides now prohibited in Europe due to their toxicity and the wider harm they cause to the environment, there are fewer options for controlling the mosquitoes.

Made with Flourish

Insect birth control

Dr Jérémy Bouyer, a biologist and mosquito expert at the French Agricultural Research Centre for International Development (CIRAD) in Montpellier, predicts Europe could face an uncontrolled dengue epidemic within the next five to ten years unless more is done to control mosquito populations. 

‘The Aedes tiger mosquitoes are very difficult to control,’ said Dr Bouyer. The insects tend to breed on relatively small sites, which makes targeting them difficult, he said. ‘Rather than ponds or lakes, they like human-made habitats.’ 

But we may not be entirely defenceless against these mosquito pests. Dr Bouyer is developing a new approach to combat mosquitoes as part of a research project called REVOLINC. Over the next few years, he will be releasing tens of thousands of sterile male yellow fever mosquitoes on Reunion Island, a French territory in the Indian Ocean.

When released, the males should mate with wild females and produce sterile eggs, and so suppress the numbers of mosquito larvae. However, the males will also be coated with a secret weapon – a biopesticide called pyriproxyfen, which mimics hormones in insects and restricts their growth. The males transfer this biopesticide onto the female when they try to mate with them, and she contaminates her eggs and larvae habitat. It means eggs fertilised by unsterilised males are also unable to mature from larvae into adult mosquitoes.

‘Even if the sterile males don’t succeed with the females, they still transmit the biopesticide,’ said Dr Bouyer. ‘We have shown that this might increase the impact of control by between 10 and 100 times, so we might need to release fewer male mosquitoes.’

To rear enough insects, Dr Bouyer and his colleagues have developed technologies for veritable mosquito factories at the International Atomic Energy Agency (IAEA) facility in Seibersdorf, Austria, where the larvae are reared on stacks of trays submerged in water, each supporting 18,000 of the wrigglers. The larvae are then sorted by sex when they pupate before the young males are sterilised with a finely balanced dose of radiation – enough to achieve almost complete sterility, but leaving them healthy enough to be able to mate when released. The sterile males can then be shipped in chilled boxes.

Drone attack

On Reunion Island, male mosquitoes were previously released in canisters placed on the ground. But 90% of the insects will not travel more than 100 metres from this spot.

In an attempt to improve the distribution of the sterile male insects, Dr Bouyer is also working on a project called MOSQUAREL, which will use drones to release mosquitoes from the air. He has already used a 12kg drone in Brazil to release 50,000 sterile male mosquitoes per flight and is hoping to trial a lighter 900g drone capable of releasing 30,000 mosquitoes at a time. The advantage of this smaller drone is that it would be permitted to fly over residential areas in Europe.

‘To treat a city with sterile insects, you need to drive a vehicle along roads, stop every 100 metres and release a box of mosquitoes,’ said Dr Bouyer. ‘It takes two hours for two vehicles to treat 30 hectares.’ A drone launched from the back of a truck could treat the same area in ten minutes, he said, and is quicker, cheaper and distributes the insects more evenly over an area.  

The new drone will also be tested in Valencia, Spain, with the release of sterile tiger mosquitoes in a citrus tree production area, in collaboration with the Spanish state-owned rural development company Tragsa

Dr Bouyer is also hoping to use the drone to release sterile yellow fever mosquitoes coated with biopesticide on Reunion Island, targeting three small populations of mosquitoes.

But while Reunion has a few isolated pockets of yellow fever mosquitoes, which Dr Bouyer hopes to wipe out, tiger mosquitoes are a bigger problem on the island. Reunion has experienced an increase in dengue fever cases since the beginning of 2018, and a particularly bad outbreak this year brought a number of deaths. Warmer temperatures and wet conditions have allowed tiger mosquitoes to flourish, so Dr Bouyer plans to target these insects next. But releasing sterile males coated with biopesticide alone will not work.

Both Aedes mosquito species only need minuscule amounts of water for their larvae, which often develop on rubbish items, in discarded plastic or in old tyres. So reducing such man-made larval habitat in urban areas will also be necessary to ensure the drone drops can have more of an impact.

‘If we suppress them in one site, then we can prevent dengue around there,’ said Dr Bouyer. ‘That is the best success we could hope for – to protect people.’

The research in this article was funded by the EU. If you liked this article, please consider sharing it on social media.

This post Sterilised insects could help control mosquito-borne diseases was originally published on Horizon: the EU Research & Innovation magazine | European Commission.

Millions of genetically-modified mosquitoes will be deployed to save Floridians from bites

Florida will become home to 750 million genetically-modified mosquitoes. Local authorities have approved the release of these insects in a bid to bring down the numbers of local mosquito swarms.

Image via Pixabay.

Mosquitoes suck — more to the point, they suck our blood. Not only is this really annoying and itchy, it can also be dangerous: mosquitoes are carriers of diseases like dengue fever and Zika, which they spread by coming into contact with the blood in our veins.

Engineered to fail

Aedes aegypti, the most common type of mosquito and so the one most likely to be biting you in your sleep, is in fact an invasive species in Florida. They’re typically found near standing pools of water, where they lay their eggs and spend their larval days.

Because nobody has much love for them, we’ve come to rely on pesticides to keep them away or, ideally, very dead. But the insects have developed a resistance to such compounds.

In order to keep their numbers in check, Florida officials have approved the release of around 750 million genetically-modified mosquitoes into the wild. All these mosquitoes, known as OX5034, are males, and carry a special gene that will kill off any female offspring they have. Since only female mosquitoes need to bite for blood (which they use as nutrients for eggs), this would dramatically limit the threat they pose to public health.

This decision comes after the US Environmental Agency granted permission to Oxitec, a British-based company operated in the US, to produce these modified mosquitoes.

The approval of this release was not without its critics. Environmental groups warn that we don’t know enough about how such mosquitoes behave in the wild to know for sure that it’s safe to release them. Their biggest worries are the creation of hybrids between wild and modified mosquitoes, and possible damage to the ecosystems that these insects are part of. An online petition on Change.org that plans to stop the US being “a testing ground for these mutant bugs” has also gathered nearly 240,000 signatures so far.

Oxitec rebuts that the issue has been studied amply and that the release should go without a hitch. Either way, the insects are set to be released in 2021 in the Florida Keys islands.

This isn’t the first time that modified mosquitoes have been used to try and control wild populations. They were previously also used in Brazil to combat Zika, and Oxitec said the results of that experiment were “positive”. It plans to also deploy the mosquitoes in Texas beginning sometime next year — although the company hasn’t gotten state or local approval as yet, it did receive the green light on the federal level.

“We have released over a billion of our mosquitoes over the years. There is no potential for risk to the environment or humans,” an Oxitec scientist told AP news agency.

Yum or yuck? Scientists find how mosquitoes evolved a taste for human blood

Not a lot of people know this, but out of the 3,500 mosquitoes species out there, just a few bite humans. This immediately begs the question: what’s so special about these species and their relationship with humans?

In a new study, researchers investigated the evolutionary pathways that enabled some mosquitoes to adapt to human settlements and grow a taste for our blood.

The yellowfever mosquito Aedes aegypti. Credit: Wikimedia Commons.

According to the new study, increased population density played a major role in mosquito adaptation to human blood. However, a dry climate was even more important.

That’s quite an important insight to have, considering mosquitoes — small and annoying as they may be — are known to spread dangerous infectious diseases. For instance, the findings suggest that increased urbanization in the coming years might increase mosquito biting and the risk of disease in tropical regions and beyond.

“We found that different African populations of the mosquitoes that spread dengue, Zika, chikungunya, and yellow fever vary widely in how attracted they are to humans. Mosquitoes living near dense cities were more willing to bite humans than mosquitoes in rural areas, but climate was even more important: in places with intense dry seasons mosquitoes showed a strong preference for humans,” Noah Rose, a researcher at Princeton University and co-author of the new study, told ZME Science.

“Mosquitoes that prefer humans showed differences in the same sets of genes, so we think this preference evolved just once about 5,000-10,000 years ago, likely as an adaptation helping them survive long dry seasons. Many cities in Africa are growing extremely quickly; our model suggests that mosquitoes in these places may evolve greater preference for human hosts, which could lead to them spreading disease more effectively.”

The Princeton researchers focused on their attention on Aedes aegypti, a highly successful mosquito species that inhabit areas in tropical, subtropical, and in some temperate climates, and the primary vector of infection for dengue, Zika, yellow fever, and Chikungunya virus.

In the grand scheme of things, Aedes aegypti is an oddity because it is one of only a handful of species from Africa that bite humans. The researchers used this to their advantage since it allowed them to empirically verify where specifically mosquitoes interact with humans the most and where they prefer to bite other animals instead.

“This study was very challenging to conduct, because we had to collect mosquitoes from a really wide range of habitats across a huge geographic range. So we were collecting mosquitoes everywhere from in the middle of a rainforest to the middle of a huge bustling city. Each of these places has unique challenges, whether it’s watching out for dangerous wild animals like lions and elephants, or getting out of a giant traffic jam on a busy city street. This was only possible because of the experience and expertise of our whole scientific team, which included people with years of experience in each of the countries and habitats in which we collected mosquitoes,” Rose said.

Using special traps, the team collected Ae. aegypti from outdoor sites in more than 27 locations across sub-Saharan Africa. In the lab, mosquitoes from each population were exposed to various animal scents (such as guinea pigs, quail, and humans) in a controlled environment in order to assess their preferences. The analysis of the recorded data suggests that mosquitoes from dense urban cities were attracted to people more than those from rural or wild areas.

But since this pattern of preference for human odors only held in extremely dense modern cities, it is highly unlikely that this was the original reason why Ae. aegypti mosquitoes evolved to bite humans.

The secondly identified pattern of mosquito preference for human blood seems more revealing and points to a more plausible avenue for genetic adaptation. Specifically, the researchers found that the insects that lived in drier, hotter regions had a strong preference for human scent when compared to other animal scents.

Somewhat counter-intuitively, the climate seems to have mattered more than having many blood bags on two legs in close quarters. Even more surprisingly, many mosquitoes living in dense cities don’t particularly prefer to bite human hosts — it is only when cities become extremely dense and are located in areas with intense dry seasons that our blood becomes very enticing to the insects.

“I think it’s because mosquitoes in habitats with intense dry seasons become particularly dependent on humans for their life cycle. Aedes aegypti larvae live in small, contained bodies of water. In the ancestral state, this was places like tree-holes or sometimes rock pools. Later, they adapted to surviving in human-associated containers like pots of stored water, or more recently buckets and tires,” Rose wrote in an email.

“In places with long, hot dry seasons, there are very few natural habitats for mosquitoes, but they may be able to survive year round by taking advantage of the habitat that humans make for them by keeping water stored near their homes. So these mosquitoes have a very close relationship with humans, which may have led them to specialize on biting humans.”

Genes concentrated in a few key regions of the mosquito genome seems to have driven this evolutionary shift in the insects’ biting preferences.

The researchers also modeled how climate change and expected urban growth might shape mosquito preferences in the near future — and it doesn’t look too good.

While climate change isn’t expected to cause important changes in dry season dynamics in sub-Saharan Africa over the next 30 years, many cities are expected to expand massively.

“Surprisingly, when we checked what our model predicts for near-term climate change in the next few decades, we didn’t see major changes in the precipitation variables that are important for mosquitoes. However, cities are growing extremely quickly, so we saw that our model predicts more human-biting in many cities across Africa due to urbanization effects. Longer term climate change could drive important behavioral shifts, but we haven’t extended our model that far — in the near term the urbanization effects seem to be more important,” Rose said.

In the future, Rose and colleagues will further investigate the interplay between climate, genetics, and urbanization in mosquitoes’ biting preferences.

“Overall, we hope this study will help people understand that all mosquitoes are not the same. Some spread disease much better than others. Even within species, there is enormous diversity. Mosquito history and human history are intertwined, and global changes driven by humans are also likely to drive further mosquito evolution,” Rose concluded.

The findings appeared in the journal Current Biology.

One gene can turn mosquitoes from females to males, which don’t bite

Researchers at Virginia Tech have found that they can turn female Aedes aegypti mosquitoes into males by tweaking a single gene in their DNA.

Image via Pixabay.

The findings could help us reduce the spread of mosquito-borne diseases. Female mosquitoes need to bite mammals in order to absorb their blood — which is converted into nutrients for their eggs. Males, on the other hand, don’t. They spend their days sipping on nectar.

Mosquito bites create an ideal opportunity for diseases such as malaria, Zika, or Dengue to spread, as they involve a small amount of the insect’s saliva entering the victim’s tissues. Shifting the ratio towards males can thus nip such diseases in the bud.

Changing demographics

“The presence of a male-determining locus (M locus) establishes the male sex in Aedes aegypti and the M locus is only inherited by the male offspring, much like the human Y chromosome,” said Zhijian Tu, a professor in the Department of Biochemistry in the College of Agriculture and Life Sciences, lead author of the study describing the process.

“By inserting Nix, a previously discovered male-determining gene in the M locus of Aedes aegypti, into a chromosomal region that can be inherited by females, we showed that Nix alone was sufficient to convert females to fertile males. This may have implications for developing future mosquito control techniques.”

The team produced several such gene-modified mosquitoes that express an extra copy of the Nix gene that is activated by its own promoter.

This sex conversion was found to be highly effective and “stable over many generations in the laboratory”, the team explains, suggesting that it would be useful in wild populations without constant reintroduction of modified mosquitoes.

However, these converted males can’t fly naturally. In order to remedy this, the team found that a second gene (myo-sex) needs to be added to the M locus as well. The team inactivated the myo-sex gene in wild-type males to confirm its function — and these insects lost their ability to fly.

Flight is important for these sex-changed insects as mosquitoes rely exclusively on flight for feeding, mating, and escaping predators. In other words a flightless mosquito, no matter how well-engineered, won’t do us much good. This being said, however, the authors report that sex-changed males were still able to father sex-converted offspring if they were presented with an anesthetized wild female.

All in all, the Nix gene has great potential as a tool to reduce the population of biting mosquitoes, and thus, the spread of disease. However, there’s still a lot of work to be done in the lab before such insects can be released into the wild.

The paper “Nix alone is sufficient to convert female Aedes aegypti into fertile males and myo-sex is needed for male flight” has been published in the journal Proceedings of the National Academy of Sciences.

A newly-found microbe could stop mosquitoes from spreading malaria

Malaria, a life-threatening disease typically found in tropical climates, is transmitted through the bite of a mosquito that was infected with the Plasmodium parasite. Symptoms include fever, chills, headache, anemia, convulsions, and sweating.

In 2018, the World Health Organization (WHO) estimated 228 million cases of the mosquito-borne disease, and that they would lead to 405,000 deaths. The WHO, governments, and researchers have long been working on different approaches to tackle the disease, but progress has stalled in recent years.

But what if we could go to the source and prevent the mosquitoes from being infected? That was the question researchers from Kenya and the UK asked themselves, having found a microbe that protects the mosquitoes and could thus help to control the disease.

The malaria-blocking microbe, called Microsporidia MB, was discovered by the researchers on the shores of Lake Victoria, Kenya. They couldn’t find a single mosquito carrying the microbe and also harboring the malaria parasite there.

The protection given by the microbe was later confirmed by further laboratory analysis. Microsporidias are fungi, or at least closely related to them, and most are parasites. However, this new species may be beneficial to the mosquito.

“The data we have so far suggest it is 100% blockage, it’s a very severe blockage of malaria,” Dr Jeremy Herren, from the International Centre of Insect Physiology and Ecology in Kenya told the BBC. He added: “It will come as a quite a surprise. I think people will find that a real big breakthrough.”

The idea that a mosquito microbe could be stopping the transmission of a disease isn’t exactly new. Wolbachia, a genus of bacteria that naturally occurs in mosquito populations, has shown incredible potential for wiping out dengue and other mosquito-borne infections.

This new research is currently in its early stages. Because Microsporidia MB is passed down the maternal line, once it’s in the mosquito population, it’s unlikely to be going anywhere. The team found that some mosquito populations in some areas they tested already had 9% of individuals infected with the malaria-busting microbe.

Microsporidia MB could be priming the mosquito’s immune system, so it is more able to fight off infections. Or the presence of the microbe in the insect could be having a profound effect on the mosquito’s metabolism, making it inhospitable for the malaria parasite.

The researchers are investigating two main strategies for increasing the number of infected mosquitoes. Microsporidia forms spores that could be released en masse to infect mosquitoes. Or male mosquitoes (which don’t bite) could be infected in the lab and released into the wild to infect the females when they have sex

“It’s a new discovery. We are very excited by its potential for malaria control. It has enormous potential,” Prof Steven Sinkins, from the MRC-University of Glasgow Centre for Virus Research, told the BBC.

The scientists need to understand how the microbe spreads, so they plan to perform more tests in Kenya. However, these approaches are relatively uncontroversial as the species is already found in wild mosquitoes. It also would not kill the mosquitoes, so it would not have an impact on species that rely on them for food.

The research was published in Nature Communications.

Malaria-bearing mosquitoes are evolving insecticide-resistant feet

Two major mosquito species that carry malaria are developing resistance to insecticide through their feet. A new study reports on how this impacts the efficiency of anti-mosquito nets, anti-malaria efforts, and a potential way forward.

Image via Pixabay.

Binding proteins in the feet of Anopheles gambiae and Anopheles coluzzii mosquitoes are helping them resist the insecticides embedded in mosquito nests, explains the team at the Liverpool School of Tropical Medicine (LSTM). As these species represent two of the most important malaria vectors in West Africa, it could undo “decades” of progress against the disease.

Net gonna get me

“We have found a completely new insecticide resistance mechanism that we think is contributing to the lower than expected efficacy of bed nets,” explains Dr. Victoria Ingham, first author. “The protein, which is based in the legs, comes into direct contact with the insecticide as the insect lands on the net, making it an excellent potential target for future additives to nets to overcome this potent resistance mechanism.”

The team found higher than average levels of the binding protein SAP2 in the insecticide-resistant species of Anopheline mosquitoes. These levels elevated further elevated levels following contact with pyrethroids, the class of insecticides used in bed nets. However, when the genes encoding this protein are partially silenced, the insects lost their resistance to pyrethroids.

As insecticide resistance grows across mosquito populations, the team explains, new insecticide-treated bed nets containing the synergist piperonyl butoxide (PBO) and pyrethroids are being introduced. Such netting targets one of the most effective and widespread resistance mechanisms mosquitoes posses, but they are always evolving new ones. The authors hope that their discovery could help point to other potentially dangerous adaptations by mosquitoes.

“Long-lasting insecticide treated bed nets remain one of the key interventions in malaria control,” explains Professor Hilary Ranson, the paper’s senior author.

“It is vital that we understand and mitigate for resistance within mosquito populations in order to ensure that the dramatic reductions in disease rates in previous decades are not reversed.”

The paper “A sensory appendage protein protects malaria vectors from pyrethroids” has been published in the journal Nature.

Multidrug-resistant malaria spreading across Southeast Asia

Malaria carrying mosquitoes have caused the extinction of more than two dozen bird species in Hawaii. Should they be destroyed using irreversible gene editing before other birds meet the same fate? Credit: Wikimedia Commons

Malaria carrying mosquitoes have caused the extinction of more than two dozen bird species in Hawaii. Should they be destroyed using irreversible gene editing before other birds meet the same fate? Credit: Wikimedia Commons

Malaria is a serious and possibly fatal disease, caused by a parasite that typically infects a certain type of mosquito. The parasite that causes malaria is Plasmodium.

There are five types: Plasmodium falciparum, Plasmodium malariae, Plasmodium vivax, Plasmodium ovale, and Plasmodium knowlesi. But P. falciparum is the most worrisome.

The first symptoms of malaria – fever, headache, and chills – usually appear 10–15 days after the bite of an infected mosquito. Left untreated, P. falciparum malaria can progress to severe illness and death. Although it has been eliminated in developed countries, malaria is still prevalent in multiple areas around the world. Worldwide, 3.2 billion people (about half the world’s population) are at risk of contracting malaria. Every 2 minutes, a child dies of malaria. And each year, more than 200 million new cases of the disease are reported.

New studies recently in The Lancet Infectious Diseases warns that malaria could “become a potential global health emergency”. An aggressive strain of drug-resistant malaria that originated in Cambodia has rapidly spread into neighboring countries, causing high rates of treatment failure to first-line treatment and complicating efforts to eliminate the disease.

One study found that the KEL1/PLA1 strain of P. falciparum now accounts for over 80% of the malaria parasites in northeastern Thailand and Vietnam. Researchers also found that the strain acquired novel genetic mutations that have allowed it to become resistant to dihydroartemisinin-piperaquine, a form of artemisinin-based combination therapy (ACT) that has been the first-line treatment for malaria in Cambodia for over a decade now and more recently adopted by Thailand and Vietnam as the treatment of choice.

The other study found that the average failure rate for dihydroartemisinin-piperaquine treatment in Cambodia, Vietnam, and Thailand is now 50%, suggesting a new first-line option is needed to fight the mosquito-borne disease in those countries.

An earlier study in The Lancet reported that KEL1/PLA1 parasites first appeared in western Cambodia in 2008, shortly after dihydroartemisinin-piperaquine was introduced. By 2013 KEL1/PLA1 parasites had migrated to northern Cambodia and Laos. By 2015 and 2016, the parasites were identified in Thailand and Vietnam. Resistance to the treatment was first reported in Cambodia in 2013.

To determine the extent of the spread of the KEL1/PLA1 parasites and the type of genetic mutations that have driven the spread, Professor Olivo Miotto, PhD, of the Wellcome Sanger Institute and University of Oxford and a team of researchers analyzed whole-genome sequencing data from P. falciparum samples collected from malaria patients in Cambodia, Laos, northeastern Thailand, and Vietnam from 2008 through 2017. The data came from the MalariaGEN P. falciparum community project, which provides researchers with sequencing data on samples from 28 countries.

From a data set of 1,673 whole-genome sequences, the team found that 1,615 had KEL1/PLA1 status, and that the prevalence of the co-lineage—a combination of an artemisinin-resistant lineage that carries mutations to the kelch13 gene and a piperaquine-resistant lineage that carries amplifications of the plasmepsin 2 and 3 genes—increased steadily over the 10-year study period. Before 2009, KEL1/PLA1 was only in western Cambodia, but by 2016-2018 it accounted for more than 50% of samples in all the countries except for Laos. More than 80% of the most recent samples in northeastern Thailand and Vietnam were KEL1/PLA1.

The data suggests that multiple KEL1/PLA1 subgroups were able to spread rapidly across borders in separate transmission waves, following the acquisition of one of several mutually exclusive mutations. The spread of KEL1/PLA1 is having a negative impact on malaria treatment in the region.

The authors of the study suggested that given the high rates of treatment failure, dihydroartemisinin-piperaquine “should no longer be used for the treatment of P. falciparum malaria in the eastern Greater Mekong subregion.” Cambodia has switched to another artemisinin-based combination therapy (ACT), artesunate-mefloquine.

“Our study provides a clear picture of how malaria that is resistant to the first-line treatment is spreading, and demonstrates the importance of using genetics to detect patterns of resistance in each area. Active genomic surveillance is now vital to inform national malaria control programmes, to help reduce the risk of a major global outbreak,” Professor Dominic Kwiatkowski, a senior author on the paper from the Wellcome Sanger Institute and the Big Data Institute at University of Oxford, said.

The potential spread of ACT-resistant malaria to Africa is particularly alarming since 90% of malaria-associated deaths occur on the continent.


Mosquitoes hunt first by smell, then by eyesight

Smelling is key if you’re a hungry female mosquito, a new study reports.


Image via Pixabay.

A team of researchers led by members from the University of Washington has looked at the brains of female mosquitoes in real-time to understand how they identify, track, and home in on their next meal. The process integrates information from the visual and olfactory sensory systems, they report. The insect’s olfactory system catches the scent of its target and triggers chemical changes in the brain of the female mosquito that makes her visually scan her surroundings for specific types of shapes and fly toward them.

Smell first, find targets later

“Our breath is just loaded with CO2,” said corresponding author Jeffrey Riffell, a UW professor of biology. “It’s a long-range attractant, which mosquitoes use to locate a potential host that could be more than 100 feet away.”

Only female mosquitoes feed on blood — the guys dine on pollen. However, this also means that only female mosquitoes bite people and spread diseases such as malaria. The present research comes as an effort from the team to better understand how the insects find their prey (or ‘hosts’) to bite, which could help develop new methods to control and reduce the spread of mosquito-borne diseases.

The olfactory cue that triggers the hunting behavior in female mosquitoes is carbon dioxide (CO2), Riffell’s prior research has shown. For the insects, smelling CO2 is a telltale sign that a potential meal is nearby, “priming” their visual systems to hunt for a host — so the team focused their study on this gas. They analyzed the changes triggered by CO2 in mosquito flight behavior and recorded how it impacts the brain activity in the olfactory and visual centers.

Data was collected from roughly 250 individual mosquitoes during behavioral trials conducted in a small circular arena, about 7 inches in diameter. The arena was fitted with a 360-degree LED display frame, and each mosquito was tethered in the middle of the rig using a tungsten wire. The mosquito’s wings were monitored from below with an optical sensor, while the LED display showed different types of visual stimuli and odors were fed into the area using an air inlet and vacuum line. What the team wanted to see was how the tethered Aedes aegypti mosquitoes responded to visual stimuli and puffs of air rich in CO2.

The researchers report that one-second-long puffs of air with 5% CO2 — for comparison, we exhale air containing 4.5% CO2 — made the mosquitoes beat their wings faster. Certain visual elements (a fast-moving starfield for example) didn’t much influence their behavior. Other elements (the team used a horizontally moving bar)  caused the mosquitoes to beat their wings faster and attempt to steer in the direction of the bar. This response was more pronounced if researchers introduced a puff of CO2 before showing the bar.

“We found that CO2 influences the mosquito’s ability to turn toward an object that isn’t directly in their flight path,” said Riffell. “When they smell the CO2, they essentially turn toward the object in their visual field faster and more readily than they would without CO2.”

The team also repeated the experiment with a genetically modified Aedes aegypti strain created by Riffell and co-author Omar Akbari, an assistant professor at the University of California, San Diego. The neurons in this strain’s central nervous system were engineered to glow fluorescent green when active.  The team could cut a small portion of the mosquito’s skull and use a microscope to record its neuronal activity in 59 areas in the lobula (part of the optic lobe) in real time.

When the mosquitoes were shown a horizontal bar, two-thirds of those regions lit up, the team reports, suggesting a response to the visual stimulus. When exposed to a puff of CO2 before being shown the bar, 23% of the regions had even higher activity than before. This indicates that the CO2 primed the areas of the brain that control vision to elicit a stronger response to the bar. The authors report that the reverse — a horizontal bar triggering increased activity in the parts of the mosquito brain that control smell — didn’t happen.

“Smell triggers vision, but vision does not trigger the sense of smell,” Riffell concludes.

“Olfaction is a long-range sense for mosquitoes, while vision is for intermediate-range tracking. So, it makes sense that we see an odor — in this case CO2 — affecting parts of the mosquito brain that control vision, and not the reverse.”

Mosquitoes can pick up scents over 100 feet away, the authors explain in their paper. Their eyesight, however, is most effective at distances of between 15 to 20 feet.

The paper “Visual-Olfactory Integration in the Human Disease Vector Mosquito Aedes aegypti” has been published in the journal  Current Biology.

What an asshole. Credit: Wikimedia Commons

Why mosquitoes bite me more than others

What an asshole. Credit: Wikimedia Commons

What an asshole. Credit: Wikimedia Commons

I’ve been engaged in an epic battle with mosquitoes for as long as I can remember. While every other kid was looking forward to summer, I could only shiver at the inevitable blisters my arms and legs would suffer.

My grandmother used to tell me I have “sweet blood”, which was very convenient for these tiny vampires. I cut candy out of my diet, but I still got bitten. Okay, so sweet blood is bullshit. But that still didn’t change the fact that I was targeted far more often than other people. Then I realized I wasn’t alone — apparently, I’m part of a select group of people listed on the mosquito’s menu as a delicacy. Dammit! What’s your beef with us, you freakin’ vampires?

Well, luckily I grew up to become a science writer. My forays confirm that mosquitoes are attracted to some people more than others. As to why, the jury isn’t out yet — there is a combination of factors that make me look like a light bulb for these bloodsuckers. The fact that there are over 3,500 species of mosquitoes, some varying in dietary choices more than others, doesn’t help, either.

[panel style=”panel-info” title=”Why mosquitoes want to suck your blood” footer=””]First of all, it’s only the female mosquito that bites hosts. The benign males munch on flower nectar instead.

Female mosquitoes feed on blood, but not for their own nutritional purposes. After piercing the skin with its mouthpart, the hypodermic needle-like proboscis, the female mosquito starts sucking the blood out and into its abdomen. It is here that the blood is digested to produce eggs. They need the protein and other components in the blood to produce their eggs. [/panel]

In the United States, some 175 mosquito species have been identified, the most common of which are Anopheles quadrimaculatus, Culex pipiens, Aedes aegypti and Aedes albopictus. So, research that involves these mosquito species should be the most relevant.

First, we should start with what we know for sure: mosquitos, the females specifically, identify targets by sensing carbon dioxide. Why CO2? Because all vertebrates produce it, so mosquitos found that being able to detect this chemical marker offered them an evolutionary advantage. Using their maxillary palp organ, mosquitos can ‘sniff’ carbon dioxide from as far as 150 ft (40m).

Right off the bat, this explains why mosquitos will come after you more frequently and in greater numbers when you’re exercising outside: you’re breathing harder and releasing more carbon dioxide than usual. Overweight individuals will also release more carbon dioxide because their bodies need more oxygen. Generally speaking, the higher your metabolic rate, the easier it will be for mosquitos to find you. This also serves to explain why pregnant women or people who drink alcohol attract more of the winged villains. For the same reason, adults are more prone to mosquitos than children, as are men more than women.

Of course, mosquitos rely on other cues as well besides carbon dioxide since living, blood-flowing vertebrates aren’t the only ones producing this gas (for example, mosquitos don’t attack trees). So to navigate and find a worthy host, mosquitoes also make use of visual markers. For instance, dark clothing is more attractive to the mosquitoes than the lighter kind. Besides coloring, mosquitos also use motion detection, so if you’re moving around an otherwise stationary environment you’re a sitting duck.

Another marker is body heat. While CO2 tells the mosquito how to find you, your warmest parts of the body, which are also the most vascularized, tell the annoying critters where to bite. The most vulnerable body parts are the neck, inner elbow, backs of knees, armpits, and wrists.

There’s also evidence that suggests mosquitoes are attracted to certain smells. Among their favorites are lactic acid, ammonia, uric acid, carboxylic acid, and octenol (however, they seem to hate the smell of chickens). These compounds can be found in the sweat and breath. A 2011 study also found a few types of bacteria made skin more appealing to mosquitoes. The ankles and feet host the most robust bacterial colonies, which might explain why these are so prone to biting.

Finally, my grandma was half-right. Mosquitoes seem to be attracted to certain blood types more than others. Studies suggest Type O individuals are the tastiest. But ultimately, what makes some stand out more than others in the face of mosquitoes is governed by genetics. Joe Conlon, PhD, technical advisor to the American Mosquito Control Association, says genetics account for a whopping 85% of our susceptibility to mosquito bites.

Genetically modified fungus wipes out 99% of malaria-carrying mosquitoes

Credit: Aedes Albopictus.

Although progress in combating malaria has been phenomenal, the mosquito-borne infectious disease is now on the rise in the most affected countries in Africa. Worldwide, about 220 million people are infected each year by a dangerous parasite that is transmitted to humans through the bites of infected mosquitoes. Naturally, scientists looking to eradicate malaria are finding that stopping its vector — the mosquitoes — is the most effective course of action. In a new study, researchers genetically modified a fungus to produce a spider toxin. Within 45 days, the fungus had killed 99% of mosquitoes capable of carrying malaria without affecting other insects.

The study was conducted inside a “mosquitosphere” — a 6,500-sq-ft (600-square-meter) dummy village in Burkina Faso, complete with plants, water and food sources, homes. The entire fake village was encapsulated in a double layer of mosquito netting in order to prevent any creatures from escaping the habitat.

Researchers at the University of Maryland in the USA and the IRSS research institute in Burkina Faso released 1,500 mosquitoes inside the village, whose numbers quickly soared thanks to the perfect breeding conditions and lack of predators. But then the research team introduced the enhanced fungus, genetically engineered with instructions that produce a toxin found in the venom of a funnel-webs spider native to Australia.

The fungal spores were mixed with sesame oil and wiped on black cotton sheets. When the insects landed on the sheets, they immediately became exposed to the deadly fungus  Within 45 days, there were only 13 mosquitoes left, the authors reported in the journal Science.

No other insects, such as bees, were infected by the fungus. Only certain species of mosquitoes of the Anopheles genus — and only females of those species — can transmit malaria. Malaria is caused by a unicellular parasite called a Plasmodium, which undergoes a series of infection steps before arriving at the mosquito’s salivary gland, from which it ultimately spreads to bitten humans.

“Deployment of transgenic Metarhiziumagainst mosquitoes could (subject to appropriate registration) be rapid, with products that could synergistically integrate with existing chemical control strategies to avert insecticide resistance,” the authors concluded.

These findings suggest that his approach may be effective in controlling the spread of malaria. However, releasing gene-edited creatures into the wild might have unintended consequences, which is why the method needs to be seriously vetted in order to ensure bio-safety. The authors also emphasize that this technology isn’t meant to wipe out mosquitoes but rather to control them and the spread of disease.

Previously, researchers have devised other tricks meant to curb the spread of malaria, including CRISPR gene edits that make mosquitoes less likely to get infected by parasites that cause malaria in humans and even drugs that could make human blood toxic to mosquitoes.

Algeria and Argentina are now malaria-free

Malaria is a mosquito-borne disease caused by Plasmodium parasites. In 2017 an estimated 219 million cases of malaria occurred worldwide and 435,000 people died, mostly children in the African Region.

The World Health Organization (WHO) announced this week that Algeria and Argentina have achieved certification of malaria-free status, meaning both have interrupted local transmission for at least 3 consecutive years.

Algeria, where the disease was first discovered in humans in 1880 by the French physician Dr. Charles Louis Alphonse Laveran, is only the second country in its African region to reach malaria-free status. The first was Mauritius, which was certified in 1973. Algeria reported its last indigenous malaria cases in 2013.

“Algeria has shown the rest of Africa that malaria can be beaten through country leadership, bold action, sound investment and science. The rest of the continent can learn from this experience,” said Dr. Matshidiso Moeti, WHO’s Regional Director for Africa.

Argentina is the second country in the Americas region to be certified in 45 years after Paraguay in 2018. Argentina reported its last local malaria cases in 2010. Malaria elimination was made a goal in Argentina in the 1970s. Elimination was achieved by training health workers to spray homes with insecticides, diagnosing the disease through microscopy, and effectively responding to cases in the community.

The WHO grants malaria-free certification when a country has proven that the chain indigenous transmission has been interrupted for at least the previous 3 consecutive years. Countries should also show evidence that the surveillance systems in place can rapidly detect and respond to any malaria cases and have effective programs to prevent resurgences and re-establishment.

In a WHO statement, Director-General Dr Tedros Adhanom Ghebreyesus said the two countries eliminated malaria due to the unwavering commitment and perseverance of their people and leaders. “Their success serves as a model for other countries working to end this disease once and for all.”

In recent years, 9 countries have been certified by the WHO Director-General as having eliminated malaria: United Arab Emirates (2007), Morocco (2010), Turkmenistan (2010), Armenia (2011), Maldives (2015), Sri Lanka (2016), Kyrgyzstan (2016), Paraguay (2018) and Uzbekistan (2018).

Dengue vaccine candidate looks promising in Phase 3 Trial

Yellow fever is spread by mosquitos. Image credits: James Gathany.

Dengue is a mosquito-borne disease that causes flu-like symptoms but can be lethal and kill up to 20% of those with severe dengue. In the last five decades, dengue has spread from being present in a handful of countries to being endemic in 128 countries, where about four billion people live. WHO has listed dengue as one of the top global health threats in 2019 alongside Ebola, global flu pandemic, HIV, antimicrobial resistance and many others.

Dengue cases have also increased 30-fold in this time period. In addition, more people are traveling than ever before and millions of travelers to endemic areas are also at risk of being bitten by the disease-carrying mosquitoes. A high number of cases occur in the rainy seasons of countries such as Bangladesh and India. Now, its season in these countries is lengthening significantly (in 2018, Bangladesh saw the highest number of deaths in almost two decades), and the disease is spreading to less tropical and more temperate countries such as Nepal, that have not traditionally seen the disease. An estimated 40% of the world is at risk of dengue fever, and there are around 390 million infections a year.

There is no specific treatment for dengue fever. For severe dengue, medical care by physicians and nurses experienced with the effects and progression of the disease can save lives – decreasing mortality rates from more than 20% to less than 1%. Maintenance of the patient’s body fluid volume is critical to severe dengue care.

(FILES) This file photo taken on April 4, 2016 shows a nurse showing vials of the anti-dengue vaccine Dengvaxia, developed by French medical giant Sanofi, during a vaccination program at an elementary school in suburban Manila.

The first dengue vaccine, Dengvaxia® (CYD-TDV) developed by Sanofi Pasteur was licensed in December 2015 and has now been approved by regulatory authorities in 20 countries for use in endemic areas in persons ranging from 9-45 years of age. In April 2016, WHO issued a conditional recommendation on the use of the vaccine for areas in which dengue is highly endemic as defined by seroprevalence of 70% or higher. In November 2017, the results of an additional analysis to retrospectively determine serostatus at the time of vaccination were released. The analysis showed that the subset of trial participants who were inferred to be seronegative at time of first vaccination had a higher risk of more severe dengue and hospitalizations from dengue compared to unvaccinated participants.

A new vaccine, TAK-003, is based on a live-attenuated dengue serotype 2 virus. Preliminary data through 15 months (Part 1 of the trial) showed that the vaccine met the primary efficacy endpoint of preventing virologically-confirmed dengue fever induced by any of the four dengue serotypes. In addition, the vaccine was found to be well-tolerated with no significant safety concerns.

“We are excited to publish the data in a peer-reviewed journal as quickly as possible,” said Rajeev Venkayya, MD, and President at Takeda. Part 2 of the trial will evaluate secondary outcome measures including vaccine efficacy by serotype, baseline serostatus and severity; long-term safety and efficacy evaluation (an additional 3 years) will be included in the third part of the study.

Takeda expects to file for licensure once Part 2 of the study is complete in each of the eight countries where its clinical trial took place: Brazil, Colombia, Panama, Dominican Republic, Nicaragua, Philippines, Thailand and Sri Lanka. The company plans to file in the U.S. and Europe within a year of filing in dengue-endemic countries, Venkayya said. Takeda and dengue experts are already planning ways to review the latest vaccine data with those regulators.

The Global Dengue & Aedes-Transmitted Diseases Consortium (GDAC), a group funded in part by drugmakers that works closely with WHO, scheduled a meeting for early March in Bangkok with regulators from at least six countries to take a first look at Takeda’s results, said Dr. In-Kyu Yoon, director of GDAC.

Anopheles Gambiae.

We can eradicate malaria — but we need to use new tricks

Malaria can be eradicated completely, according to new research. The study goes on to analyze why previous efforts fell short of this goal and takes a look at what new strategies could help continue our fight against this terrible parasite.

Anopheles Gambiae.

A feeding female Anopheles gambiae mosquito. A. gambiae is a known malaria vector.
Image credits CDC / James Gathany.

The early years of this new millennium were fraught with malaria. Several outbreaks of unprecedented size moved the world as a whole to take action. By 2015 the disease’s spreading rate was halved, and such efforts ground to a standstill. Countries like Zanzibar continued to deal with the disease — however, it was never completely wiped out.

A new study led by Professor Anders Björkman at the Department of Microbiology, Tumour and Cell Biology, Karolinska Institutet takes a look at why our efforts fell short in the past — some key issues being changes in mosquito behavior and natural selection of the parasites making them more drug resistant.


“But after [2015], the decline tailed off,” says Professor Björkman who has been running the Karolinska Institutet’s eponymous malaria project for 18 years. “Except for in Zanzibar, where the action taken for its 1.4 million citizens has led to approximately a 96 per cent decline in the incidence of malaria.”

“We’ve optimised these measures with the Zanzibar Malaria Control Programme and can now explain why malaria has not yet been fully eliminated.”

The world-wide anti-malaria offensive was carried largely by the development of new drugs, and the widespread distribution of anti-mosquito sprays and insecticide-infused nets. While definitely successful, such measures are lackluster today at best.

Björkman’s team has been monitoring roughly 100,000 residents from two districts in Zanzibar since 2002. Their study shows that malaria-carrying species of mosquitoes now predominantly bite people outdoors instead of indoors, as used to be the case. The insects also seem to have developed a resistance, or at least a tolerance, to modern pesticides. Finally, Plasmodium, the protozoan parasite that causes malaria, has been undergoing a process of forced natural selection at the hands of our medicine. The current form of Plasmodium is much more difficult to detect and treat but spreads with the same virulence as before.

“Both the mosquitoes and the parasites have found ways to avoid control measures,” says Professor Björkman. “We now need to develop new strategies to overcome this if we’re to attain the goal of eliminating the disease from Zanzibar, an endeavour that can prove a model for the entire continent.”

There’s a lot at stake, too. One of the findings that surprised the team most (and not in a good way) was the sheer decline in child mortality experienced in Zanzibar. Malaria control measures, they note, led to a 70% drop in overall child mortality rates. It’s an immense percentage, given that the highest estimation of malaria-related child deaths in Africa previous to this study was of only 20%. Sub-Saharan Africa currently has the highest rate of newborn deaths in the world (34 deaths per 1,000 live births in 2011) and the highest rate of date for children under five (1 in 9 children) according to the United States Agency for International Development.

This tidbit suggests that malaria has a much more dramatic and chronic effect on general infant health than we dared assume. The disease overtaxes a baby’s immune system, spreading it too thinly to defend against other pathogens. Professor Björkman considers malaria to still be “the greatest obstacle to a healthy childhood in Africa” because of this.

“If you ask African women today, their greatest concern is usually that malaria doesn’t affect their pregnancy and their babies. The global community must continue the fight for improved strategies and control measures. If this happens, I think we’ll be able to reach the goal of ultimate elimination.”

Zanzibar was chosen for this study as the country has made huge efforts to put global anti-malaria initiatives in place, and actively works to control the disease to this day. The researchers hope that their findings can guide anti-malaria strategies throughout Africa.

The paper “From high to low malaria transmission in Zanzibar – challenges and opportunities to achieve elimination” has been published in the journal BMC Medicine.

Credit: Pixabay.

Mosquitoes are eating microplastics, which they pass on to the food chain

Credit: Pixabay.

Credit: Pixabay.

British researchers claim they have the first proof that microplastics are entering the food chain by air via mosquitoes. Insect larvae have been observed ingesting microplastic particles, which are transferred into the adult form. Whatever creature that devours the insect would then become contaminated with plastic, which goes up the food chain until the contamination can make its way back to humans, the source of the plastic pollution in the first place.

Biting microplastics

Microplastics are tiny plastic waste, ranging from 5 millimeters down to 100 nanometers in diameter. Since mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem.

Ultimately, microplastics travel up the food chain where they reach humans. A portion of consumer-grade mussels in Europe could contain about 90 microplastics, according to one study. Consumption is likely to vary greatly between nations and generations, but avid mussel eaters might eat up to 11,000 microplastics a year. Microplastics have also been found in canned fish, and even in sea salt. One kilogram can contain over 600 microplastics,  meaning if you consume the maximum daily intake of 5 grams of salt, that’s equivalent to ingesting three microplastic particles a day.

[panel style=”panel-warning” title=”Microplastics” footer=””]

Microplastics can be categorized by their source. There are two main types, primary and secondary.

Primary microplastics are purposefully made to be that size. They were created by the manufacturer to be tiny for a particular purpose. The one that you have probably heard about the most are microbeads — little plastic spheres used in face washes, cosmetics, and toothpaste to exfoliate or scrub.

Secondary microplastics are bits of plastic that break down from larger pieces. Weathering, such as from waves, sunlight, or other physical stress, breaks the plastic into smaller pieces. Usually, it originates from waste that wasn’t managed properly.


Now, scientists have uncovered a new source for microplastic pollution in the global food chain. Researchers at the University of Reading observed how mosquito larvae were ingesting microplastics then passing them on through their life cycle, they reported in the journal Biology Letters. For instance, mosquitoes are eaten by birds, bats, and spiders, all of which are preyed upon in turn by other animals.

“The significance is that this is quite possibly widespread,” Amanda Callaghan, biological scientist at Reading, said in a statement.

“We were just looking at mosquitoes as an example but there are lots of insects that live in water and have the same life-cycle with larvae that eat things in water and then emerge as adults.”

[panel style=”panel-success” title=”Why microplatic pollution is a huge environmental concern” footer=””]

Microplastics never dissolve and stay in the ocean forever. Plastic does not biodegrade because it is new to the environment and bacteria have not evolved to break down the carbon-carbon links found in plastic. Plastic can constantly be broken down into smaller pieces but will always remain there. Only if and when bacteria evolve the ability to break down plastic on a large scale (there have been some isolated cases) will the plastic be biodegraded. Let’s not count on that. Major changes need to follow on an industrial (such as for fleeces and tires) and governmental level (such as laws for managing ocean waste).


Although the mosquito larvae were observed maturing into adulthood in laboratory conditions, the researchers are confident that the same microplastic transfer is happening in the wild.

How much harm microplastics actually do to humans is still an open question. These recent findings, however, suggest that the microplastic problem is extremely broad and complex because the pollution has permeated virtually all creatures and environments.

In order to tackle microplastic pollution, some countries have banned certain sources of primary microplastics such as microbeads. Secondary microplastics, however, account for the vast majority of such pollution and a clear-cut solution is not yet in sight.

West Nile.

Indiana’s health officials warn of West Nile virus spotted in mosquitoes in Elkhart, Carroll County

Indiana state officials urge locals in Elkhart and Carroll County to take precautions after mosquitoes in the area tested positive for the West Nile virus.

West Nile.

West Nile Virus.
Image via Cynthia Goldsmith (CDC) / Public Domain.

West Nile virus is a mosquito-borne virus known to be present in Africa, Asia, Europe, and the Middle East — and, since 1999, the Americas as well. It’s quite a nasty bug. The milder form of the illness,  West Nile fever, can include fever, headache, body aches, swollen lymph glands, or a rash. More severe forms of the disease affect the nervous system and include inflammation in the brain and spinal cord (encephalitis), meningitis (inflammation of the tissues that wrap around the brain and spinal cord), muscle paralysis, even death.

It generally likes to infect wild birds. Mosquitoes bite infected birds and transmit the virus over to humans. In the US, it was first identified in wild birds in Indiana in 2001; up to now, it has been found in “most states along the eastern coast and east of the Mississippi River,” according to the Indiana State Department of Health (ISDH).

As of June 27, the ISDH released a warning to locals in Elkhart and Carroll County (link goes to the ISDH’s live monitoring of the virus) that the virus has been detected in mosquitoes in the area. State Health Commissioner Kris Box adds that there is no need to panic. No human cases have been detected as of now, and it’s actually not that uncommon for West Nile to be spotted around these parts — it happens every year. The ISDH expects to continue to see increased West Nile activity throughout the state as the mosquito season progresses.

State officials urge residents to take precautions — especially since the risk of infection is highest during the summer months. Some of the ways you can protect yourself from infection with the virus include:

  • Avoid being outdoors when mosquitoes are active, especially late afternoon, dusk to dawn and early morning.
  • Apply an EPA-registered insect repellent containing DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol to clothes and exposed skin.
  • Cover exposed skin by wearing a hat, long sleeves, and long pants in places where mosquitoes are especially active, such as wooded areas.
  • Install or repair screens on windows and doors to keep mosquitoes out of the home.

Residents should also take the following steps to eliminate potential mosquito breeding grounds:

  • Discard old tires, tin cans, ceramic pots or other containers that can hold water.
  • Repair failing septic systems.
  • Drill holes in the bottom of recycling containers left outdoors.
  • Keep grass cut short and shrubbery trimmed.
  • Clean clogged roof gutters, particularly if leaves tend to plug up the drains.
  • Frequently replace the water in pet bowls.
  • Flush ornamental fountains and birdbaths periodically.
  • Aerate ornamental pools, or stock them with predatory fish.

Mosquito saliva can affect your immune system up to a weeks

Even if the mosquito isn’t carrying any dangerous pathogens, its saliva causes a reaction that can be detected for weeks after the bite.

Mosquito spit may affect your immune system for days. Image credits: Rico-Hesse et al, 2018.

Summer is just around the corner and that means that everyone’s least favorite insect is making a comeback — the mosquitoes are coming soon, to a moist area near you. But mosquitoes are more than just a nuisance. Around the world, 750,000 people a year die of mosquito-transmitted diseases, including malaria, dengue, West Nile, Zika, and chikungunya fever. Recent studies have shown that mosquitoes do more than “just” transmit the infection — the mosquito saliva exacerbates some of these diseases, and infections caused by a mosquito bite are often more severe than similar infections caused by a needle, for instance.

Even when it doesn’t carry an infection, the mosquito saliva contains hundreds of proteins that can affect our immune system. For starters, it causes inflammation that isn’t just itchy, but also helps potential viruses multiply and quickly spread to other parts of your body. Now, in a new study, scientists have shown that the impact of the mosquitoes’ saliva lasts much longer than expected.

Rebecca Rico-Hesse, of Baylor College of Medicine, USA, and colleagues wanted to study the effect of mosquito bites on human immune cells. But they didn’t want to have subjects bitten by mosquitoes (and no ethics committee would be happy to hear that idea) — so they came up with a different solution. They engrafted mice with human hematopoietic stem cells (stem cells that give rise to other blood cells) — leading the animals to have components of a human immune system. They then had each mouse bitten by four mosquitoes and monitored the behavior of these immune cells for several days.

“Understanding how mosquito saliva interacts with the human immune system not only helps us understand mechanisms of disease pathogenesis but also could provide possibilities for treatments,” the researchers say.

The team found that the immune responses lasted up to 7 days post-bite. Furthermore, they were seen in multiple tissue types, including the blood, skin and bone marrow. The fact that the effects lasted for so long and managed to elicit such a strong immune response is a reason for concern.

While it’s not clear exactly how this effect manifests itself, this is the first time measurements of this kind were ever carried out and, undoubtedly, the results will have major implications for the future study of mosquito saliva and its effect on the human body. In the long run, this could also enable researchers to develop better vaccines, by indicating which proteins to target for the long-term effect.

Journal Reference: Vogt MB, Lahon A, Arya RP, Kneubehl AR, Spencer Clinton JL, et al. (2018) Mosquito saliva alone has profound effects on the human immune system. PLOS Neglected Tropical Diseases 12(5): e0006439. https://doi.org/10.1371/journal.pntd.0006439

Mosquito swarm.

Malaria makes its hosts smell better to draw more mosquitoes, research finds

Malaria can change the way you smell, drawing more mosquitoes, a new study shows. The results might explain how the disease is able to spread so effectively.

Mosquito swarm.

Image credits Petra Boekhoff / Pixabay.

Malaria, a disease caused by the parasite genus Plasmodium and spread by mosquito bite, could make you more attractive to the insects. Its findings come to flesh out previous research which found that the parasites change the smell of animals they infect. The work also shows one of Plasmodium‘s more insidious mechanisms, in which it lures mosquitos in towards infected individuals, super-charging its spread.

Maybe she’s born with it, maybe it’s malaria

The research, led by Ailie Robinson from the Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, tested participants outside of the lab, dissecting their body odors to see which elements of its chemical makeup matter to mosquitoes.

The team’s smelly research brought them in contact with the socks of 45 Kenyan schoolchildren — some of them infected by malaria, others not. To see whether mosquitos displayed any preference towards the smell of those infected with Plasmodium, the team placed socks in a test device, formed out of two boxes linked by a tube. Then, they released mosquitos into the tube and tracked which sock they flew toward.

The insects showed a preference for the socks worn by infected children, the team reports. When presented with a choice between these socks and ones worn by the same child 3 weeks after the infection was treated with medication, 60% of the mosquitos chose the ‘infected’ sock. When presented with two pairs of socks collected at different times from children that were never infected, the mosquitoes didn’t show any preference one way or the other.

Now that they knew something in the scent of malaria-infected individuals made them more attractive to mosquitos, the team wanted to find out exactly what that ‘something’ was. They analyzed foot odor samples obtained from 56 children, obtaining the full list of chemicals that constituted the scents. Then, they puffed each chemical at a time over mosquito antennae attached to electrodes.

This testing zeroed in on aldehydes, a class of chemicals including heptanal, octanal, and nonanal — organic molecules constructed out of chains of seven, eight, and nine C atoms respectively, which impart fragrance to spices, fruits, and perfumes among others. These compounds were found in higher levels in the samples of infected children and elicited a strong electrical response from the antennae.

‘Smells like something I’d bite’

It’s possible that malaria is promoting its spread by making the scent of infected individuals more alluring to mosquitoes. The more insects that the plasmodium can goad into biting these individuals, the more chances the infection has of spreading to other people says study co-leader James Logan, a medical entomologist at the London School of Hygiene & Tropical Medicine.

However, the team isn’t certain what’s behind this difference in odor. It could be that the aldehydes are secreted by the parasite itself, or that they may be produced when the host’s fat cells break down during the infection, the team notes. They caution, however, that while the come-hither effect may be unique to malaria, it’s possible the shift in odor is common to other diseases as well.

“The malaria parasite is sort of manipulating the system both in the mosquito host and the human host,” Logan says. “It’s very clever.”

“This is probably specific to malaria, but it could be that other infections could cause the same effect.”

Understanding odor’s effect in the spread of malaria could help us detect infection sooner and nip its transmission in the bud. Alternatively, it could lead to the creation of better mosquito traps. Getting the bouquet just right is quite tricky, though — the team notes that even small tweaks in scent mixes they produced in the lab will influence whether mosquitos are piqued or indifferent. In one seemingly paradoxical case, the insects were drawn to a scent spiked with a small dose of heptanal, but decidedly unimpressed when the amount of the chemical was increased slightly.

The paper “Plasmodium-associated changes in human odor attract mosquitoes” has been published in the journal Proceedings of the National Academy of Sciences.

Credit: Public Domain.

Drug could make human blood deadly toxic to mosquitoes

New research finds that malaria-carrying mosquitoes died after bitting people who had taken high doses of ivermectin, a drug meant to fight parasites. This means the drug might one day become part of national malaria control programs.

Credit: Public Domain.

Credit: Public Domain.

Only certain species of mosquitoes of the Anopheles genus — and only females of those species — can transmit malaria. Malaria is caused by a single-celled parasite called Plasmodium, which undergoes a series of infection steps before arriving at the mosquito’s salivary gland, from which it ultimately spreads to bitten humans.

Each year, the disease infects more than 200 million people, causing 429,000 deaths — and things aren’t taking a turn for the better. Despite billions spent on malaria eradication programs, we seem to have reached a plateau. Mosquitoes are becoming increasingly resistant to insecticides, which is forcing researchers to think of all sorts of new solutions like a malaria vaccine.

Some proposed solutions, however, can be quite dramatic, like genetically engineering mosquitoes so they wipe themselves out.

This is why it’s so exciting to hear that a drug that is already on the market can serve a double role in malaria control. Ivermectin was developed in the 1980s to ward off parasites that cause river blindness and elephantiasis. In the last 30 years, over two billion treatments of ivermectin have been distributed.

Previously, several studies found that malaria-carrying mosquitoes would die after sucking the blood from individuals who had taken ivermectin. Now, an international team of researchers investigated in a controlled setting the precise conditions when this can happen.

Researchers gave 47 participants exactly 600 milligrams of ivermectin in tablet form for three days in a row. Blood samples were then drawn from each participant six times, then fed to trapped mosquitoes. The typical annual dose for the drug is 200 milligrams, so the participants were on a very high dose. Despite this, there were no side effects reported. As a caveat, the participants were already in the hospital infected with malaria and might not have shown any side effects since they already sick.

Two weeks after the mosquitoes were fed with blood from the 600mg-group, 97% of the insects had died. The blood from another group of 48 patients who were given a 300 mg dosage was not nearly as effective. When researchers at the Imperial College London plugged the results in a mathematical model, they found that the high dose ivermectin could reduce malaria incidence by as much as 61%.

More studies need to be done to establish the efficacy and safety of a high ivermectin dose against malaria. However, the results so far are extremely promising, suggesting a drug that’s already been vetted for decades might become a promising new weapon in our anti-malaria arsenal.

“This first evaluation of the impact of high dose ivermectin on mosquito mortality is highly encouraging and requires further evaluation in larger scale trials that target both malaria parasites and the mosquitos, as the world pushes towards malaria elimination,” explained Feiko ter Kuile, a Professor at the Liverpool School of Tropical Medicine (LSTM) and senior author of the paper.

“The drug’s impact on mosquito mortality, long effect-duration, and tolerability make it a promising new tool in malaria control. It has a different mode of action from other insecticides, meaning that it could also be effective against mosquitos that rest and feed outdoors, as well as mosquitoes that are resistant to the standard insecticides used on bed nets and indoor spraying.”

The findings were reported in the journal The Lancet Infectious Diseases.