Scientists Seek Better Ways to Combat Mosquito-Borne Illnesses

Summer has arrived, and the extended periods of warm weather in the United States increases the risk of exposure to insect-borne viruses. Beyond the seasonal weather, international travel and trade contribute to the spread of these illnesses.

The number of insect-borne diseases reported to the Centers for Disease Control and Prevention tripled from 2004 to 2016, according to a recent agency report. During this period, several disease-causing pathogens have had their moments in the spotlight—the West Nile, chikungunya, and Zika viruses, and the mostly recently identified mosquito-borne virus in humans, Keystone.

Insects such as mosquitoes and ticks carry viruses, bacteria, or parasites that can be transmitted to humans and cause disease. Scholars and fellows in the Pew biomedical programs are tackling these public health threats from multiple angles, using approaches that could help reduce the incidence of illnesses such as malaria, Zika, and dengue.

Exploring mosquito evolution and behavior

Carolyn (Lindy) McBride, a 2015 Pew scholar from Princeton University, has been trying to decipher what leads mosquitoes to bite humans. She investigates genes and neuronal circuits that help dictate mosquito behaviors that allow them to survive in human surroundings.

McBride has studied the differences between forms of Aedes aegypti mosquitoes to understand why the brown “domestic” type is more attracted to human odor than the black “forest” type. Her lab recently launched a population genomics project—called PipPop—to look at the evolutionary history of the northern house mosquito, Culex pipiens. This is the main carrier of the West Nile virus and exists in two forms: a cold-adapted version that primarily bites birds and a warm-adapted version that bites mammals. By examining the underlying mechanisms causing these behavioral differences, McBride’s work could inform new strategies to repel mosquitoes.

Searching for biological weapons to fight mosquitoes

With limited availability of vaccines to prevent illnesses transmitted by mosquitoes, the most common method of controlling the populations is with insecticides. As an alternative, health officials in Florida have tried using genetically modified mosquitoes to drive out the disease-carrying insects.

Heverton Dutra, a 2017 Pew fellow at Boston University, is working to use the bacterium Wolbachia to control mosquito-borne illnesses. Recent research has shown that insects infected with this bacteriumhave limited capacity to transmit pathogens to hosts. Dutra is developing a new strainthat could be more efficiently introduced into mosquitoes—and maintain itself within the mosquito population from generation to generation.

His work could allow scientists to study how Wolbachia acts to fight insect-borne viruses, which remains unclear, and provide a mechanism to curb disease transmission.

Strategies for a malaria vaccine

Mosquitoes infected with the parasite Plasmodium falciparum spreadmalaria around the world, and the debilitating disease affects millions of people. The only malaria vaccine, developed in the 1980s and approved by European regulators in 2015, provides protection for young children but has relatively low efficacy, leaving room for improvement.

Erol Fikrig, a 1993 Pew scholar at Yale University, is working on a new vaccine that targets the mosquitoes directly instead of the malaria parasite. Fikrig noticed that the saliva deposited by malaria-infected mosquitoes can affect parasite transmission. A recent study outlines the work done by his group to develop a serum that attacks a key protein in mosquito saliva, reducing the movement of the parasite into the skin of the host. The serum worked against different strains of malaria and could potentially be used to boost the protective effect of existing vaccines.

Public health approaches can help fight mosquito-borne diseases

Eva Harris, a 2001 Pew scholar at the University of California, Berkeley, is a professor of infectious disease and vaccines. Her research focuses on the transmission of the virus that causes dengue fever and explores strategies to better provide the resources needed to help address insect-borne illnesses in developing countries.

One aspect of her lab’s research involves investigating factors in the immune system that play a role in disease severity and protection from mosquito-borne diseases. In 1998, Harris founded the Sustainable Sciences Institute (SSI), a nonprofit that aims to strengthen scientific and public health infrastructure in resource-poor settings.

Today, SSI continues to help in the development of sustainable local research and public health systems, and trains people to identify, respond, and control infectious disease outbreaks. For example, the SSI team has worked with responders in Paraguay and Peru during a dengue fever outbreak and helped the Nicaraguan health ministry prepare for chikungunya in Central America.

Kara Coleman directs The Pew Charitable Trusts’ biomedical programs, including the biomedical scholars, Pew-Stewart Scholars for Cancer Research, and Latin American fellows programs.