Behavioral Resistance: Mosquitoes Learn to Avoid Bed Nets | American Council on Science and Health

By Alex Berezow 

Credit: Shutterstock

Malaria is a notoriously tricky infectious disease. Because of a unique genetic flexibility, it is able to change surface proteins, avoiding the immune response and greatly complicating vaccine development. Furthermore, the parasite is transmitted by mosquitoes, which are difficult to control. Insecticides work, but mosquitoes can develop resistance to them.

One method widely used to control malaria is for governments or charities to provide families with insecticide-treated bed nets. Overall, this strategy is very successful, and it has been credited with preventing some 451 million cases of malaria in the past 15 years. But bed nets are not successful everywhere. In some parts of the world, mosquitoes develop “behavioral resistance”; i.e., they learn to avoid bed nets by biting people earlier in the day.

A team led by Lisa Reimer of the Liverpool School of Tropical Medicine monitored mosquito behavior in villages in Papua New Guinea before (2008) and after (2009-2011) the distribution of bed nets. Data from one of the villages, Mauno, depicts a very noticeable shift in mosquito feeding behavior. (See graphs on the right.)

Before bed nets were distributed in 2008, the median biting time for mosquitoes was around midnight. After the distribution, the median time shifted back to 10 pm. Also, a greater proportion of mosquitoes took their dinner even earlier, from 7 to 9 pm. 

Worryingly, it’s unclear whether the bed nets were effective at preventing malaria transmission. The number of bites per person per night dropped after the introduction of bed nets, but started to climb in subsequent years as mosquitoes began to adapt. Additionally, the prevalence of malaria infection in humans — arguably, the only statistic that actually matters — dropped in one village, remained the same in a second, and ticked up slightly (albeit insignificantly) in a third.

Despite the mixed results in Papua New Guinea, Dr Reimer believes that bed nets should continue to be used worldwide as part of a mosquito control strategy. However, she notes that behavioral resistance may prove just as vexing as insecticide resistance and, in some locations, may limit the efficacy of bed nets.

Thus, mosquitoes must be monitored for both behavioral and insecticide resistance, as the little creeps stubbornly refuse to die and may be cleverer than we thought.

Source: Edward K. Thomsen et al. “Mosquito behaviour change after distribution of bednets results in decreased protection against malaria exposure.” J Infect Dis. Published: 22-December-2016. doi: 10.1093/infdis/jiw615

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Simple mosquito killers are the new buzz in Gates Foundation’s malaria battle | The Seattle Times

Research team members check an attractive toxic sugar bait station on the outside wall of a home in Mali. In preliminary tests, the stations, which attract and kill malaria-carrying mosquitoes, caused populations of the bloodsuckers to plummet. (Westham Innovations)
Research team members check an attractive toxic sugar bait station on the outside wall of a home in Mali. In preliminary tests, the stations, which attract and kill malaria-carrying mosquitoes, caused populations of the bloodsuckers to plummet. (Westham Innovations)

Vaccines and genetic engineering grab the spotlight, but the Bill & Melinda Gates Foundation’s quiet funding for simple, new mosquito controls could be about to pay off in the effort to eradicate malaria.

 

Seattle Times science reporter

Since Bill and Melinda Gates galvanized the global health world with their 2007 call to eradicate malaria, researchers have been scrambling for new tools to get the job done.

The lineup includes headline-grabbing marvels like genetically engineered mosquitoes, a laser fence to zap the malaria-carrying bugs and a silver-bullet vaccine. But there’s no telling when — or if — any of those technologies will actually pan out.

Meanwhile, a less flashy Bill & Melinda Gates Foundation initiative could be about to pay off with two potentially game-changing new ways to kill mosquitoes. Though simple and environmentally friendly, both approaches crashed mosquito populations in initial field trials in Africa.

Private companies already exist to commercialize the products, which could be deployed within a few years. And both also show promise for helping Americans battle mosquitoes in their own backyards.

“There’s lots of innovation, lots of cool ideas for malaria, but we really need things that can start saving lives in a timeline of three to five years,” said Penn State University entomologist Matt Thomas. “Simply having a great idea that sits on the lab bench isn’t going to do that.”

Humble insecticides have been the workhorse of every successful malaria elimination drive, including those that banished the disease from the United States and Europe. Since 2000, malaria deaths worldwide have fallen by half, and almost 80 percent of the gains are attributed to wider use of insecticide-treated bed nets and indoor spraying.

It’s cheaper and easier to develop new methods of mosquito control than to develop and gain approval for new drugs or vaccines, said Dan Strickman, a senior program officer at the Gates Foundation. But mosquitoes will eventually develop resistance to any conventional insecticide. Almost since its founding the Gates Foundation has been quietly investing in research on novel insecticides — while also searching for entirely new ways to control mosquitoes.

The two new technologies, which Strickman says could be “transformational,” capitalize on mosquito behavior. One turns an entire house into a toxic trap using humans as bait. The other lures mosquitoes with the scent of their primary food — which isn’t blood.

“These are tools that don’t just replace something that we do now,” Strickman said. “They do something different.”

The house trap was dreamed up under a mango tree in a Tanzanian village where Thomas, Dutch entomologist Bart Knols and colleagues gathered for a brainstorming session.


 

One of the topics was an odd preference on the part of malaria-carrying mosquitoes for slipping into houses via the gap between the walls and roof that’s common in many African dwellings. The scientists came up with the idea of inserting plastic tubes, called eave tubes, under the roofline and closing off the rest of the gap.

The mosquitoes, which bite indoors at night, are lured into the tubes by the scent of humans in the house. But instead of a tasty blood meal, the insects encounter a pesticide-coated mesh insert that douses them with poison.

With funding from the European Union, the researchers tested the concept by building an experimental village inside a screened enclosure the size of two tennis courts. They seeded a small marsh with malaria-free mosquitoes to establish a self-sustaining population and recruited volunteers to act as bait, sleeping in houses equipped with eave tubes and window screens.

The results were “incredible,” Strickman said. “The mosquitoes were basically gone, without spraying, without a lot of use of insecticides.”

The Gates Foundation was so impressed that the giant philanthropy bypassed its normal funding channels and anted up $10.2 million for large-scale tests that will include malaria monitoring.

The work will start early next year in 40 villages in the West African nation of Ivory Coast. Half the villages will get eave tubes, while the other half will use conventional mosquito control, Thomas explained.

Computer modeling suggests that installing eave tubes in even half the homes in some African communities could have a significant impact on malaria, he added. After the initial cost of installation, the only expense would be replacing the insecticide-coated inserts a couple of times a year.

A Dutch company, In2Care, is already manufacturing the tubes and is part of the research. “This is a tool that can be made field-ready,” Thomas said.

Workers drill holes along the roofline of a house in Kenya to install eave tubes to kill malaria-transmitting mosquitoes. In initial trials, mosquito populations in the village crashed.  (Penn State University)
Workers drill holes along the roofline of a house in Kenya to install eave tubes to kill malaria-transmitting mosquitoes. In initial trials, mosquito populations in the village crashed. (Penn State University)

Eave tubes target mature female mosquitoes, which only feed on blood in order to produce eggs. The other new approach to mosquito-killing exploits the insects’ main food source — which is nectar.

Watching mosquitoes flit around flowers gave Israeli scientists the inspiration for using sugar to lure mosquitoes into a trap. The team got an early grant from the Gates Foundation, and was later funded by the U.S. military.

What emerged is the concept called attractive toxic sugar bait, or ATSB.

“It’s entirely new,” Strickman said. “There’s never been a real attract-and-kill product for mosquitoes before.”

The idea is to use a bait that draws mosquitoes with its sweet scent, but is mixed with a small amount of insecticide. “As long as the mosquitoes come and feed on these things, they’re going to die,” Strickman said.

It took years of trial and error with solutions ranging from guava juice to fermented fruit brews for the scientists to develop a long-lasting, patented bait based on dates and sugar. A variety of insecticides can be used, including benign compounds like boric acid and garlic oil.

Tests in Israel and West Africa showed that use of toxic sugar bait, either as a spray or bait stations, can reduce mosquito populations by 90 percent or more. It seems to work well even in places with a lot of natural sugar sources, like flowers and rotting fruit.

The approach is especially powerful because it can kill males and young females, Strickman said. But early versions also killed bees and other pollinators. The newest bait stations, which encapsulate the lure and insecticide in a flat, black membrane, don’t seem to attract beneficial insects, but more research is needed, said University of Miami environmental health expert John Beier, a member of the project science team.

The Gates Foundation is funding large trials in Mali through the UK-based Innovative Vector Control Consortium.

The Israeli-based manufacturer Westham Co. is a key player in the trials and is already thinking about how to gear up for commercial production, Strickman said. Equipping a house with two long-lasting bait stations could cost as little as $5 and could be enough to control local mosquito populations, he added.

“We hope to have a product in Africa on the market as early as 2019,” Strickman said.

Research on eave tubes and toxic sugar baits has already generated products for mosquito control in the U.S. and other developed countries.

Researchers tested the effectiveness of attractive toxic sugar bait stations on mosquitoes released inside screened enclosures in the West African nation of Mali.  (Westham Innovations)
Researchers tested the effectiveness of attractive toxic sugar bait stations on mosquitoes released inside screened enclosures in the West African nation of Mali. (Westham Innovations)

Americans can buy a sugar-based spray from Terminex that kills mosquitoes with garlic oil, or hire the company to have their property sprayed. Backyard bait stations aren’t available yet but eventually will be, Beier said.

“I would certainly buy one at Home Depot if I could,” he said.

In2Care, the company that makes eave tubes, also produces stand-alone mosquito traps that use the same type of insecticide-coated mesh to deliver the fatal dose. The traps were recently approved for emergency use in the U.S. against the mosquitoes that transmit Zika, dengue and other viruses.

Funding from Gates and others has created a golden age in what’s called vector control — the unglamorous slog of battling mosquitoes, said Karl Malamud-Roam, manager of Rutgers University’s public health pesticides program.

“There hasn’t been any time in the last hundred years when so many new … ideas have been floating around, with people who care and money to test things,” he said.

For malaria, the next challenge will be to figure out what mix of mosquito killers will work best in combination with existing medical treatments to beat back the disease and shrink its footprint over the next 10 to 15 years, he said.

By that time, some of the futuristic techniques like genetic engineering or a better vaccine might be ready for prime time, said Thomas, of Penn State.

“Hopefully, at that point they will be just mopping up.”

Some of the reporting for this story was conducted during a fellowship sponsored by Malaria No More, which is partly funded by the Bill & Melinda Gates Foundation.

Malaria superbugs threaten global malaria control, scientists say

More than half the world’s people are at risk of malaria infection

By Kate Kelland

LONDON, Feb 2 (Reuters) – Multidrug-resistant malaria superbugs have taken hold in parts of Thailand, Laos and Cambodia, threatening to undermine progress against the disease, scientists said.

The superbugs – malaria parasites that can beat off the best current treatments, artemisinin and piperaquine – have spread throughout Cambodia, with even fitter multidrug resistant parasites spreading in southern Laos and northeastern Thailand.

“We are losing a dangerous race to eliminate artemisinin resistant…malaria before widespread resistance to the partner antimalarials makes that impossible,” said Nicholas White, a professor at Oxford University in Britain and Mahidol University in Thailand who co-led the research.

“The consequences of resistance spreading further into India and Africa could be grave if drug resistance is not tackled from a global public health emergency perspective.”

More than half the world’s people are at risk of malaria infection. Most victims are children under five living in the poorest parts of sub-Saharan Africa.

Recent progress against the mosquito-borne disease has been dramatic and numbers falling ill have been significantly reduced, but it still kills more than 420,000 people each year, the World Health Organization says.

Malaria specialists worldwide say emerging drug resistance in Asia is now one of the most serious threats to that progress.

From the late 1950s to the 1970s, chloroquine-resistant malaria parasites spread across Asia and then into Africa, leading to a resurgence of malaria cases and millions of deaths.

Chloroquine was replaced by sulphadoxine-pyrimethamine (SP), but resistance to SP subsequently emerged in western Cambodia and again spread to Africa.

The fear now is that the same pattern of resistance spread and the resurgence will repeat itself.

“We now see this very successful resistant parasite lineage emerging, outcompeting its peers, and spreading over a wide area,” said Arjen Dondorp, of the Mahidol Oxford Tropical Medicine Research Unit in Thailand, who co-led the work.

Efforts to control malaria in Asia must be stepped up urgently “before it becomes close to untreatable”.

In their study in the Lancet Infectious Diseases journal, the scientists said that after examining blood samples from malaria patients in Cambodia, Laos, Thailand and Myanmar, they found that a single mutant parasite lineage, known as PfKelch13 C580Y, has spread across three countries, replacing parasites containing other, less artemisinin-resistant mutations.

They explained that while the C580Y mutation does not necessarily make the parasite more drug-resistant, it does have other qualities that make it more risky – notably it appears to be fitter, more transmissible and able to spreading more widely.

(Reporting by Kate Kelland; Editing by Angus MacSwan)

Malaria infection depends on number of parasites, not number of mosquito bites by Hayley Dunning

For the first time, researchers have shown that the number of parasites each mosquito carries influences the chance of successful malaria infection.

The finding has implications for vaccine development and studies into how the disease spreads in the field.

The findings, from scientists at Imperial College London, may also explain why the only registered malaria vaccine, RTS,S, has had only partial efficacy in recent trials. Malaria is spread when mosquitoes bite humans and release microscopic parasites, which live in the salivary glands of the mosquitoes, into the person’s bloodstream.

These findings could have significant implications for public health. We have shown that the concept of relying on the number of bites alone to predict malarial burden is flawed.

– Dr Andrew Blagborough

The parasites then travel to the liver, where they mature and multiply for 8-30 days before spreading throughout the bloodstream and causing the symptoms of malaria.

Not every infectious mosquito bite will result in malaria. To determine the intensity of malaria transmission, researchers and international organisations like the World Health Organisation currently rely on a measure called the entomological inoculation rate (EIR): the average number of potentially infectious mosquito bites per person per year.

However, this does not take into account how infectious each of those bites may be – each bite is considered equally infectious. Previous studies using needle-injected parasites have suggested this may not be the case, but there have been no comprehensive studies using biting mosquitoes, which more accurately reflect real-world scenarios.

Now, in a study funded by the PATH Malaria Vaccine Initiative and the Medical Research Council, published in the journal PLoS Pathogens, researchers have determined that the number of parasites each individual mosquito carries influences whether a person will develop malaria. Some mosquitoes can be ‘hyperinfected’, making them particularly likely to pass on the disease.

Significant implications

In studies in mice, the researchers determined that the more parasites present in a mosquito’s salivary glands, the more likely it was to be infectious, and also the faster any infection would develop.

Study co-author Dr Andrew Blagborough, from the Department of Life Sciences at Imperial, said: “These findings could have significant implications for public health. We have shown that the concept of relying on the number of bites alone to predict malarial burden is flawed, and has probably hampered the successful use of control measures and the development of effective vaccines.

“It is surprising that the relationship between parasite density and infectiousness has not been properly investigated before, but the studies are quite complex to carry out.”

The team set up repeated cycles of infection, so that groups of infected mosquitoes containing variable numbers of parasites repeatedly bit sedated mice, transmitting malaria to them under a range of transmission settings.

This allowed them to track how many individual parasites different mosquitoes harboured, how many mice were infected as a result of exposure to them, and how long it took the mice to develop malaria.

Vaccine development

By conducting further studies with mice and human volunteers, the team were also able to explain why the malaria vaccine RTS,S is effective only around 50 percent of the time, and why any protection rapidly drops off after three years.

Vaccine development has come a long way, and this new insight should help future vaccine studies to be tested more rigorously.

– Dr Thomas Churcher

The vaccine was less effective when mice or humans were bitten by mosquitoes carrying a greater number of parasites. The researchers think this is because the vaccine can only kill a certain proportion of the parasites, and is overwhelmed when the parasite population is too large.

All malaria-affected regions will have a mix of mosquitoes carrying different parasite amounts. Dr Blagborough said: “The majority of mosquitoes in the wild are either uninfected or infected at quite low levels, but some individual mosquitoes are regularly very highly infected.

“As the levels of malaria drop in an area due to the successful use of interventions, the number of these hyperinfected mosquitoes is expected to drop – but they’re not totally prevented unless the intervention is very powerful.”

Study co-author Dr Thomas Churcher, from the MRC Centre for Outbreak Analysis and Modelling at Imperial, said: “Vaccine development has come a long way, and this new insight should help future vaccine studies to be tested more rigorously.

“However, in the end, it is unlikely that one magic bullet will eradicate malaria, and we should continue to seek and apply combinations of strategies for reducing the burden of this disease.”

Dr Morvern Roberts, programme manager for global infections at the Medical Research Council who funded the research, said: “Researchers have long wondered whether the more malaria parasites in a mosquito’s mouthparts, the more likely they are to infect a host with the disease. No one has been able to demonstrate this until now but the authors of this paper have shown that this is the case in both mouse models and in humans.

“As they suggest, this knowledge is extremely important to take into account when trying to develop vaccines for malaria and other vector-borne diseases.”

Water scarcity as a lead cause to Obesity and Diabetes: an outlook at the rural California

Although water scarcity affects every continent of the globe with around 1.2 billion people(UN) in dire need, it is now becoming very clear that places such as California are not spared of this preventable problem.
I read an interesting article written by Colleen Curry in the Vice News that rural communities in California have increased their intake of sugary and soda drinks thus predisposing them to Obesity and Type 2 Diabetes.
The report, which was contained in a policy paper, also noted that even those that have access to clean drinking water do buy the sugary and soda drinks out of the fear of consuming contaminated water.
Still, and to show the increasing disparity between the affluent and the low-income minority populations, it was observed that the prevalence of Type 2 Diabetes and Obesity is higher among the low-income population. The other factors to this growing scourge include environment hazards, lack of education, and lack of access to healthy foods and nutrition.
Arguably this could be considered as one of the negatives of Globalization; hence the need for global public health leaders to come together once again and address the ever increasing health inequality.

WHO experts chart next steps for Ebola vaccine trials

I am sharing this beautiful piece on Ebola vaccine trials that I read on the CIDRAP website; enjoy.

The next steps in testing Ebola vaccines as well as a picture of how they might be used in West Africa’s outbreak region became clearer today as officials from the World Health Organization (WHO) shared the outcome of yesterday’s high-level meeting in Geneva.

Large phase 3 trials in West Africa’s outbreak setting will be next up to see if the vaccines work, with the studies designed to collect more safety data, a task usually covered in phase 2 trials, experts involved in the meeting said today at a WHO media telebriefing. However, as Ebola infections drop off in the outbreak region, scientists face a closing window of opportunity to see how the vaccines perform in a real-life setting.

Experts also signaled a possible role for two Ebola vaccine formulations: a single-dose vaccine providing shorter-term immunity that could be used to tamp down Ebola flare-ups and a prime-boost vaccine that may provide more durable immunity and could be used for other immunization strategies.

Vaccine landscape evolves
Marie-Paule Kieny, PhD, the WHO’s assistant director-general for health systems and innovation, said the group’s review of phase 1 clinical trials of the two vaccines furthest along in testing found acceptable safety profiles, but information on what dose stimulates an ideal immune response won’t be known for 2 to 4 more weeks.

While 2014 will be remembered as the year Ebola challenged humanity, 2015 will be remembered as the year humanity used the best scientific minds to fight back against the disease, she said, and the fast-tracking of the vaccines has been unprecedented. “I can assure you there has been no holiday for the many people working on that.”

Helen Rees, MBBS, a professor at the University of Witwatersrand who led the meeting, told reporters that progress made at the meeting was very encouraging and that each of the affected countries had strong delegations that were deeply engaged.

Yesterday’s meeting was the second to work out details about Ebola vaccine clinical trials and how to finance eventual vaccine deployment to curb spread of the virus in Guinea, Liberia, and Sierra Leone. Since the first meeting on Oct 23, a third Ebola vaccine has entered phase 1 trials: a prime-boost combination from Johnson & Johnson, based on AdVac technology from Crucell Holland BV and MVA-BN technology from Bavarian Nordic.

Clinical trials have been under way for the past few months for the two other vaccines: a US-GSK vaccine known as ChAd3 that uses a chimpanzee adenovirus with a Zaire Ebola virus gene spliced into it, and VSV-EBOV, developed by Canadian researchers and licensed by NewLink Genetics and Merck, which uses a vesicular stomatitis virus (VSV) to carry an Ebola gene.

Developers of the Johnson & Johnson vaccine, for which phase 1 trials just launched, have overcome some delays and successfully gained some ground, Kieny said, adding that additional Ebola vaccines, including ones from groups in Russia and China, are at different stages of development. “Last year at this time the cupboard was dry, but now the cupboard is filling quickly,” she said.

The next phase of testing will take place in all three West African countries, using three completely different trial designs, which Kieny said will give researchers several good points for evaluating the vaccines.

Phase 3 study details
A randomized trial in Liberia will involve three arms (single doses of ChAd3, VSV-EBOV, and placebo), with 9,000 volunteers in each. In Sierra Leone, investigators will conduct a trial of a still-undetermined vaccine using a step-wedge design, with a goal of enrolling about 6,000 people. Meanwhile, teams in Guinea will vaccinate frontline health workers at trial sites where they will use a ring-vaccination design involving about 4,500 people, similar to an intervention used to vaccinate against smallpox.

Kieny said researchers hope to begin the Liberian trial at the end of January, with trials in Sierra Leone and Guinea projected to begin in February. She said efforts—such as sensitizing the population—are already under way to prepare for the vaccine trial. Study sites are getting special freezers to store the vaccine, but she added that developers are working on formulations that potentially allow the doses to be stored at refrigerator temperatures and that might be available in the next few months.

Experts at the meeting discussed concerns about how a continued drop-off in cases could affect the trials, Kieny said. She noted that investigators could include larger populations if they need to, though doing so might lead to some delays.

Weighing vaccine choices, outbreak needs
Looking ahead to production capacity for the three vaccines that are furthest along in trials, Kieny said robust quantities in the tens of millions are expected for VSV-EBOV as well as for Johnson & Johnson’s prime-boost vaccine, which can be stored at refrigerator temperature. However, the quantity for ChAd3 will depend on the dosage level, with a few million doses available by the middle of the year.

Rees said a separate WHO working group is exploring different strategies for deploying vaccines once they are available. Immunization plans will account for different epidemiologic patterns in each of the countries.

When asked if all the vaccine studies were taking up too much research space, Rees said there is capacity to do more than one phase 3 study and that having several vaccine candidates in the pipeline is desirable. “We can’t assume that anything is going to work,” she said, adding that once correlates of protection are known, scientists will look at how to improve the products.

She said the experts have addressed whether the vaccines will really make a difference in West Africa’s outbreak. Different epidemiologic patterns in the region will require different control approaches, and even if vaccines have limited utility in the current outbreak, they will be ready for the future. “We anticipate that this won’t be the end of Ebola.”

Other developments
In the wake of West Africa’s Ebola outbreak and criticism of slow international response, 95 members of the global health academic community signed on to a letter published in The Lancet today urging countries to redouble their efforts to invest in the WHO. They said an analysis of how the group performed in the outbreak is warranted, but added that an independent review should also consider the impact of budget cuts to the WHO and the need for sustained funding. They said international forums are floating the idea of a new “first responder” United Nations agency but that the WHO already has a system in place and any new agency would face the same funding challenges.

Urgent studies should be done to explore possible benefits of loperamide use, in combination with oral rehydration, for treating diarrhea in Ebola patients, three US-based researchers wrote yesterday in a commentary in the Journal of Infectious Diseases. In West African settings that lack the ability to provide electrolyte monitoring and replacement, antidiarrheal agents may be useful, but their use isn’t often reported and there are no safety and efficacy data to guide their use. Clinicians may be reluctant to use the drug, because it hasn’t shown a benefit for cholera-related diarrhea and can result in problems when used for some bacterial causes of diarrhea. However, they said studies have shown a benefit for other types of infectious diarrhea in adults and children older than age 2, with few safety problems. Use of loperamide seems like a rational approach that could also reduce environmental contamination, making it worthy of more study, the authors wrote.

The number of Ebola infections in the three most affected countries has risen to 21,086, with the number of deaths increasing to 8,289, the WHO said today in a brief update. The totals reflect an increase of 114 illnesses and 30 fatalities since the WHO’s update yesterday. Today’s count includes cases reported in Liberia and Sierra Leone through Jan 6 and in Guinea through Jan 7. With 10,030 illnesses reported to far, Sierra Leone remains the hardest hit country. However, Liberia still has the most deaths, with 3,515.

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