Hybrid Mosquitoes Suspected in West Nile Virus Spread.

West Nile virus has walloped the United States each year since it arrived in 1999. Mysteriously, however, there have been few human outbreaks in Europe, even though the virus is endemic there, and the birds that harbor it and the mosquitoes that transmit it are similar to those in the United States. Now, genetic analyses of mosquitoes from five continents suggest a controversial explanation for this mystery: U.S. mosquitoes that transmit West Nile virus may be hybrids of two strains. The paper's authors, led by Dina Fonseca of the Smithsonian Institution's National Museum of Natural History in Washington, D.C., who was working with Richard Wilkerson of the Walter Reed Army Institute of Research in Silver Spring, Maryland, focused on a complex of mosquitoes called Culex pipiens.