Washington-AP -- A Smithsonian Institution researcher has a theory as to why human infection by West Nile virus may be more common in North America than in Europe.
Doctor Dina Fonseca (fahn-SEE'-kuh) says it could be because of a hybrid mosquito that bites both birds and humans, carrying the virus from one to the other. She says European mosquito species tend to bite either birds or humans, but not both.
Fonseca's study, appearing this week in the journal Science, says 40 percent of the mosquito population genetically analyzed in the U-S are a type that will bite both humans and birds.
But Andrew Spielman of the Harvard School of Public Health says evidence supporting that theory is -- in his words -- "anything but solid."