Last year, a team of researchers made a surprising discovery: Aedis aegypti mosquitoes—the species that spreads West Nile Virus, dengue, chickungunya and, most recently, Zika—were living year-round in the Capitol Hill neighborhood of Washington, D.C. In a paper published in the American Journal of Tropical Medicine and Hygiene, the researchers wrote that the mosquitoes had been living in the area since at least 2011, biting and reproducing in the summer months and likely riding out the winter underground. Previously, scientists had believed that the mosquitoes couldn’t survive year-round anyplace north of South Carolina.
While the D.C. population of A. aegypti isn’t believed to carry Zika, its presence nevertheless came as a shock. And as the Zika epidemic continues to spread through Brazil, Central America, and now the United States, scientists will continue to wrestle with how environmental factors like climate change are affecting the creatures that spread infectious diseases.
Before last year, Zika outbreaks had appeared in sporadic small outbreaks near the equator in Africa, Southeast Asia, and the Pacific Islands. In May 2015, the Pan American Health Organization confirmed the first cases of Zika in Brazil; since then, the virus has spread rapidly throughout the Americas, including the first cases of Zika in the U.S. A student in Virginia contracted the virus while traveling in Central America, and public-health officials identified a case of sexual transmission in Texas.