West Nile virus still a threat: US official

By Carolyn Abate

SAN FRANCISCO (Reuters) - The West Nile virus remains a serious health risk in the United States even though the number of cases has plunged, a U.S. health official said on Thursday.

"We are entering a new phase, and we can call it the endemic phase," said Lyle Petersen, director of the Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Disease.

"The virus is here and it's going to stay," Petersen told reporters at the National Conference on West Nile Virus in the United States.

Last year 2,949 human cases of West Nile were reported in the United States, with nearly one-third occurring in California. Of those infected, 116 died.

Those figures are down dramatically from 2003, when the virus peaked at some 10,000 cases and 264 fatalities.

Petersen said the drop in cases may lead to complacency, noting the virus over the past three years was the most common infection transmitted by mosquitoes in North America.

"We have more people living in areas where West Nile virus is, and the reality is the potential for bad news has never been greater," he said.

Most West Nile victims have no symptoms. But some people develop headache, fever and fatigue, or a more serious illness such an encephalitis or meningitis that can be deadly.

There is no known cure for West Nile virus, but Petersen said initial drug trials for cures have been completed.

West Nile virus first appeared in New York state in 1999 and is spread to humans by infected mosquitoes. Scientists are able to track the virus by testing chickens and birds, which usually contract it first.

Petersen said bird surveillance systems in place to monitor the West Nile virus may serve as a model for tracking the possible spread of avian flu in the United States.