By Richard Levine
Yesterday, March 13, 2016, nearly 70 scientists, public-health officials and other participants attended the Summit on the Aedes aegypti Crisis in the Americas, a one-day meeting convened by the Entomological Society of America (ESA) and the Sociedade Entomológica do Brasil (SEB) in the city of Maceió in Alagoas, Brazil.
Although the Summit took place during the Zika crisis, the planning for it began two years ago. The Aedes aegypti mosquito was a problem long before anyone had even heard of Zika because it also transmits dengue, chikungunya, and yellow fever.
The idea behind the Summit was to explore ways for the international community of entomologists to better control mosquito-borne diseases in the Americas and around the world. In order to do this, they need to determine where more research is needed, discuss technologies and approaches that can currently be used for effective mosquito control, and they need to communicate with the public, because without their help the Aedes aegypti mosquito will not be controlled effectively.
The reason is that Aedes aegypti are container breeders that tend to live near humans. Females lay eggs in small amounts of water — in cans, bottles, old tires, rain gutters, etc. — which can be found nearly everywhere in countries like Brazil where it tends to rain a lot. Furthermore, they prefer to feed on humans more than other mammals, and they will bite multiple times during the day and the night, making them more likely to transmit viruses.
If the public is not encouraged to help eliminate standing water from their yards, gutters, and from inside their houses, then the mosquitoes will have numerous breeding areas and integrated vector management will be difficult.
Grayson Brown, past president of the Entomological Society of America and one of the co-organizers of Summit, told me that a public education campaign is needed, one that would make people understand that it is not OK to leave standing water in their yards, just as they have learned that it is not OK to drive while drunk or to smoke cigarettes in restaurants.
During the Summit, examples of similar efforts were given, including public education campaigns during the 2014 Ebola crisis in Africa. The scientists also discussed novel ways of controlling mosquitoes that do not involve traditional pesticide applications, although pesticides can still be used in integrated vector management programs.
Two of the most interesting techniques involve the use of Wolbachia, a genus of bacteria that is believed to infect about 60 percent of all insect species in the world. In some insects, Wolbachia can be harmless, or even beneficial, but for others it can be harmful, especially if insect males and females are infected with different Wolbachia strains.
In many insects, if the males and females are not infected by the same strain of Wolbachia, then their offspring will not survive. Several speakers talked about how scientists are using this to their advantage.
Basically, they raise male mosquitoes in a laboratory and essentially sterilize them by infecting them with Wolbachia. Upon release into the wild, the males mate with females that have not been infected with this strain of Wolbachia, so their offspring do not live. This is similar to the decades-old Sterile Insect Technique (SIT), which uses radiation to sterilize males, and then allows them to mate unsuccessfully with females in the wild.
Other speakers, and presenters of posters, discussed a completely different way of using Wolbachia. This method does not reduce the numbers of Aedes aegypti. Instead, it reduces their ability to spread Zika and other viruses.
Researchers discovered that a particular strain of Wolbachia called wMel blocks the mosquitoes’ ability to transmit the viruses, so instead of trying to kill mosquitoes, the goal is to spread the wMel strain throughout the mosquito population. The truly ingenious part about this is that they use female mosquitoes to do the work for them.
As discussed earlier, when Wolbachia-infected males mate with uninfected females, their offspring will not survive. However, when female mosquitoes are infected with Wolbachia and are then allowed to mate with uninfected males, their offspring WILL survive, and they will also be infected with the wMel strain of Wolbachia. The offspring will then grow to be adults, and when they mate, the next generation will also be infected with wMel. Eventually, it is hoped, the entire population will be infected, and none of the individuals will be able to transmit the viruses.
One Brazilian scientist named Frederico Muzzi showed me how he and his organization, Eliminate Dengue, are engaging the public by encouraging them to help out. Scientists distribute little cardboard cartons — the kind that are used for takeaway meals at Chinese restaurants — that contain eggs of mosquitoes that are infected with wMel Wolbachia and some food. Citizen scientists take the cartons home and then they just add water. The eggs hatch, and the larvae eat the food, eventually becoming pupae and then adults. The adults then fly away and mate with other mosquitoes, infecting them with wMel and thus ending their careers as disease vectors.
Other interesting mosquito control methods included an acoustic larvicide, a mechanical insecticide, a laser monitoring device, and genetically modified mosquitoes.
In addition to presentations about the mosquitoes and ways of controlling them, attendees also broke out into groups to discuss what needs to be done in the future. Funding for mosquito control was a subject that was brought up often. Unfortunately, most of the resources for mosquito-borne disease prevention seem to go towards medical solutions, like vaccines, medicines, or detection methods.
Now don’t get me wrong, vaccines and medicine are wonderful. However, if the mosquitoes that transmit the diseases are removed from the equation, then no one would be infected in the first place and there would be no need for medical solutions. Furthermore, when it comes to managing the disease vectors — the mosquitoes — a little goes a long way. As the old saying goes, an ounce of prevention is worth a pound of cure.
History shows that it can be done. Aedes aegypti was eradicated in Brazil (or at the very least, nearly eradicated) in the late 1950s after programs were implemented by the Pan American Health Organization (PAHO) and the World Health Organization (WHO). Hopefully, this meeting will lead to similar collaborative and successful efforts.
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Richard Levine is Communications Program Manager at the Entomological Society of America and editor of the Entomology Today Blog.