NIAID Now | July 30, 2019
For many of us, pesky mosquitoes are part of life outdoors during the summer months. While some people consistently find themselves covered in bites after an evening outside, others may rarely get bitten. This puzzling phenomenon—why mosquitoes choose to bite some people over others—is actually an important area of research for infectious disease experts. Mosquito bites can be more than just an itchy nuisance in certain parts of the world. Mosquitoes can carry parasites, viruses, and worms, and spread deadly infections. In select parts of the United States, mosquitoes have transmitted viruses such as chikungunya, dengue, West Nile, and Zika. Mosquitoes found in other parts of the world can spread filariasis and malaria—a disease that caused 435,000 deaths worldwide in 2017.
One element all mosquitoes have in common is their complex sense of smell. Mosquitoes must seek out blood meals (a mosquito “bite” to humans) to reproduce and water sources to lay eggs; however, they have poor vision and instead use scent to find their next meal.
Mosquitoes have exquisitely sensitive small hairs (known as sensillae) on their antennae and mouth parts. These hairs have scent receptors that help the mosquitoes distinguish among and select hosts. However, the scents that attract mosquitoes, and why they choose to bite some people over others, is still not well understood. Various NIAID-supported scientists hope to learn more through basic and translational research projects on mosquito olfaction (the sense of smell), host-seeking behavior, and host identification.
Researchers have long known that mosquitoes are attracted to the human scent of sweat, which includes the odor of lactic acid. The mechanisms behind this attraction remained a mystery, until recently. A NIAID-funded team of investigators have identified a unique odor receptor, known as Ionotropic Receptor 8a (IR8a), that is used by the Aedes aegypti mosquito to detect lactic acid. Led by Dr. Matthew DeGennaro of Florida International University, the research team mutated various receptors of Aedes aegypti, a mosquito that transmits diseases such as dengue and Zika, to study the effects on olfaction. When they mutated IR8a, which is located on the antennae, researchers discovered that the mosquitoes were incapable of sensing lactic acid and other acidic smells in human odor. The findings, published in Current Biology, could lead to the development of new and improved mosquito attractants and repellents. If researchers know how mosquitoes find people, they can develop novel ways to target those mechanisms.
NIAID also is applying concepts from basic research on mosquito olfaction to support the development and testing of novel tools for mosquito control. These include traps that use attractants to lure mosquitoes searching for a meal or a site to lay eggs. Scientists also are working to develop repellents, including improved, environmentally friendly products for personal and spatial protection. Investigators hope that mosquito olfaction research will lead to new ways to prevent mosquitoes from finding and biting people, and, ultimately, reduce the transmission of mosquito-borne diseases.
Reference: JI Raji et al. Aedes aegypti mosquitoes detect acidic volatiles found in human odor using the IR8a pathway. Current Biology DOI: 10.1016/j.cub.2019.02.045 (2019).