Mosquito May Tell Why U.S. Tops Europe In West Nile

Human infection by West Nile virus may be more common in North America than in Europe because of a hybrid mosquito that bites both birds and humans, carrying the virus from one to the other. European mosquito species tend to bite either birds or humans, but not both, a researcher says. A genetic study of the Culex pipiens mosquito in 33 locations in Europe has found that there are two different forms of the same species with different behaviors. One type lives underground, such as in a subway or in weather-protected areas, and one lives above ground, in the open. The underground type will bite humans, but not birds, while the above ground type favors birds.