By Johanna Elsensohn
Throughout the world, a single mosquito bite can have one of many consequences: mild infection, severe illness, birth defects, death, or, for the majority of people, just a small, itchy bite mark. Of the greater than 3,500 mosquito species out there, a small percentage have the ability to carry a pathogen that infects humans. Of those particular species, only a small fraction of individual mosquitoes actually carry a pathogen at a given time, meaning the majority of mosquitoes aren’t harmful, just a nuisance. But all it takes is one.
Humans are playing an interminable game of Russian roulette with mosquito-transmitted pathogens, and often it feels like we’re on the losing side. Viruses like yellow fever and dengue fever have been around for centuries but have yet to be eradicated. Zika virus is just the latest, but likely not the last, destructive pathogen carried by the Aedes aegypti mosquito. While the death rate from Zika is lower than other diseases, the full range of physical and neural defects is still being discovered.
At the height of the Brazilian Zika outbreak in early 2016, President Obama directed the White House Office of Science and Technology Policy (OSTP), the primary advisory body to the Office of the President on scientific matters, to coordinate federal efforts in targeting novel and existing technologies to effectively control Aedes mosquito species in the United States. The resulting report, A Strategy for Integrating Best Practices with New Science to Prevent Disease Transmission by Aedes Mosquito Vectors [PDF], was released in December by the National Science and Technology Council (NSTC), comprised of OSTP and other federal agencies. (Also see the summary White House blog post, “Vector-Control Science and Technology to Manage Zika.”) This report, while short, at least by government standards, contains a considerable amount of information as well as recommendations for future research needs.
A lot of what’s in the report isn’t new. The United Nations World Heath Organization (WHO) released research recommendations for this mosquito and virus in March 2016, and the NSTC report supports and builds on WHO’s conclusions. Briefly, the WHO recommended a multifaceted approach to controlling Ae. aegypti by combining existing methods like indoor residual insecticide sprays or personal protective measures with newer, unproven technologies, like transgenic or Wolbachia-infected mosquitoes. The NSTC report calls for increased research in these areas, including international collaborations.
Perhaps the most noteworthy aspect of the report is the call for a shift in how federal agencies and the broader research community go about developing and implementing mosquito (vector) control solutions. This report reflects a growing trend to consider and prioritize social and behavioral science alongside biological science when it comes to research that impacts humans. Described here are three of the key messages from the report, plus a final note about the future outlook:
Involve, Not Just Inform, Affected Communities
“The effectiveness of public-health interventions hinges on the extent to which control practices are implemented in communities and on the knowledge and perception of residents.”—NSTC report, p. 22
Aedes aegypti mosquitoes affect people where they live, play, and work. Many of the control tactics that exist or are in development might be highly effective, but problems potentially lie in their application. Community involvement can be a vital component of successful vector control programs, as seen in India, Brazil, Australia, and Mexico. This mosquito preferentially lives in and around human structures, so public involvement is necessary to reduce Ae. aegpyti populations. Mosquito elimination experts, like those working for Mosquito Control Districts (MCD) in the United States, can only be as effective as the impact and reach of the technologies used. Community participation can enhance MCD efforts to reduce mosquito habitats and help prevent pathogen transmission and disease spread from mosquito bites. However, communities and individuals may vary in their concern over one or more of the proposed control strategies.
For example, the U.S. Food and Drug Administration approved open field trials of a transgenic mosquito Monroe County, Florida. Local concerns and national media attention delayed the planned releases, and in November 2016 county residents were asked to vote whether or not to approve the releases in their communities. Key Haven, the original release location, voted against the transgenic mosquitoes, while the rest of Monroe County supported the use of this technology.
Social and behavioral science (SBS) research can be vital in understanding how best to engage and involve people with the mosquito management strategies being used around them. When done thoughtfully, SBS researchers can work alongside natural scientists, technology developers, and communities to develop solutions that are effective, appropriate, and responsible in controlling Ae. aegypti. Behavioral science can offer key insights into how and why people make decisions and how to encourage small changes in perception or behavior (e.g., radio jingle about GM mosquitoes)
The Need for Efficacy Research
The ultimate goal of any management strategy is to decrease the chance a female Ae. aegypti mosquito will transmit a pathogen to a human. The majority of existing and developing strategies, including insecticides, genetically modified (GM) mosquitoes, and Wolbachia, work by reducing the number of adult mosquitoes in an area, the idea being fewer total mosquitoes should translate to fewer Zika infections. Indeed, past vector control programs that reduced mosquito populations in Central and South America did lead to lower incidence of yellow fever and dengue in humans. To date though, the impact of individual strategies has not been fully assessed, even for existing technologies. (See “A Critical Assessment of Vector Control for Dengue Prevention,” May 7, 2015, in PLOS Neglected Tropical Diseases, for a review of efficacy studies to combat dengue.)
For developing technologies, GM and Wolbachia-infected Ae. aegypti mosquitoes have undergone open field trials in several countries for multiple years, but there are no major studies yet published to indicate whether the two technologies have decreased the incidence of dengue in humans. Scientists need better ways to collect data on where these strategies work well, or not, and identify areas for improvement.
Build Best Practices From the Bottom Up
Control strategies, SBS research, and training should be implemented at a local level, then scaled up. Like we saw in 2016, Zika isn’t expected to become an epidemic across wide swaths of the United States. Rather, small infestations will likely pop up in states closest to other transmission areas, like in Texas and Florida. Probable outbreak areas need to be prepared to respond quickly and effectively.
While one management plan isn’t likely to be appropriate for all U.S. communities, there will be commonalities across locations. The report specifically mentions the need for enhanced local and national expertise in several understaffed areas, including medical entomology, SBS research, mosquito control, and extension education. In fact, the Entomological Society of America is specifically cited as a resource for developing integrated vector management field technicians via its Associate Certified Entomologist certification. This multidisciplinary approach will help address social and environmental aspects of mosquito control, such as local adaptation or individual community concerns.
Will the Report and Its Messages Get Lost in Transition?
This report was released in the final days of an outgoing administration. Such strategy documents are meant to inform and guide research budgets of the appropriate—in this case, mosquito and health-related—federal agencies. The language that was used could likely make it into a Request for Applications during the fiscal 2017 funding cycle. While a new administration is about to take over, and the fiscal 2017 federal budget has not yet been fully appropriated, it is likely that most agencies will see budget allocations similar to 2016 funding levels. Subject matter reports are just one way that the president can impact science research. See “How does a US president settle on his science policy?, January 3, 2017, at The Conversation, for an excellent overview of how the Office of the President can broadly and specifically influence scientific research and policy.
“The urgency is not just in the face of today’s Zika outbreak, but to act while public attention is high and not allow a hiatus of interest to occur until the next epidemic unfolds.”—NSTC report, p. 25
As this report notes, there is urgent need for action. The next pathogen could be just around the corner. As the authors indicate, Ae. aegypti is invasive where it’s a global health problem, serves no ecological purpose in those areas, and is the primary (but not only) carrier of Zika virus. To prevent transmission, the majority of the recommended strategies will need to cause drastic reductions in mosquito populations. Political and social will cannot wane if we want to eliminate these mosquitoes as a public health threat. Texas recently confirmed the first cases of local Zika transmission, and Florida is still dealing with the aftermath of last summer’s Zika outbreak in Miami.
Though the worldwide Zika public health crisis was declared “over” by the WHO, Zika virus will likely be around for many more years. Armed with new weapons, new approaches, and new allies, perhaps we can prevent future disease transmission by Aedes mosquito vectors. As regional branch meetings of the Entomological Society of America (ESA) convene this spring, this OSTP report can stimulate discussions on how best to incorporate the recommendations into existing research programs or begin new collaborations.
Johanna Elsensohn is a Ph.D. student at North Carolina State University with a major in entomology and minors in genetic engineering and society, and biotechnology; a National Science Foundation IGERT fellow in genetic pest management; and a member of ESA’s 2015 class of Science Policy Fellows.