ATLANTA, GEORGIA--A potent form of an African bird virus has been killing blackbirds in Austria for 3 years, researchers reported here 1 March at the International Conference on Emerging Infectious Diseases. The mosquito-carried virus is spreading, raising the specter of a West Nile-like toll on birds across Europe, but so far, it does not appear to pose a major threat to humans.
The first sign of the virus came in summer 2001, when Eurasian blackbirds began to die around Vienna. From the dead birds' tissues, virologist Norbert Nowotny and others at the University of Veterinary Medicine in Vienna, Austria, isolated Usutu virus, a virus related to West Nile that was first discovered in mosquitoes in South Africa in 1959. The Usutu virus has never been reported outside tropical and subtropical Africa, where it isn't known to kill birds. But migrating swallows apparently brought it to Vienna, where it seems to be thriving, reported Nowotny.
The virus's arrival as a more virulent form makes it similar to West Nile, an African virus that appeared in the United States in 1999. Already, Usutu virus has killed 30% of the Vienna area's blackbirds as well as some great gray owls, sparrows, blue tits, and other species. Last summer, it reached the borders of Slovakia, Hungary, and the Czech Republic. "We will see in a couple of years how this develops," says Nowotny.
So far, the virus's effects on humans seem minimal. Nowotny and colleagues found antibodies in some people whose blood has been tested, and they believe that one person may have contracted rash and fever from the virus. However, hospitals have not reported a summertime rise in encephalitis and meningitis as was seen with West Nile virus, Nowotny says: "There is definitely no severe human disease."
But that's no reason to be complacent, says the University of Hawaii's Duane Gubler, who recently retired as director of the Division of Vector-borne Infectious Diseases at the Centers for Disease Control and Prevention. Gubler says West Nile Virus didn't seem to pose a threat to humans--at least at first. "Here's a virus kicking around for 60 years, and all of a sudden you have an epidemic of human disease."