PHOENIX - A top health official in Arizona's largest county warned residents Thursday that there could be a "possible epidemic" of the West Nile virus after confirmation of the first two locally acquired human cases.
Those two, and one case in New Mexico, are the first human cases of West Nile reported in the nation this season.
One of the Arizona cases was contracted last fall, but was not confirmed by health officials until this month.
"We're hoping it doesn't grow," said Dr. Jonathan Weisbuch, director of the Maricopa County Department of Public Health. "But when the virus is implanted in a community, we do see a number of cases.
"We could see several hundred cases ... a possible epidemic," added Weisbuch. "It will depend on how effectively we control the growth of mosquitoes."
The mosquito-borne virus, which has marched steadily westward since the first domestic case turned up in New York in 1999, has killed more than 560 people in the United States in the past five years.
Health officials said the virus typically causes flu-like symptoms such as fever, nausea, headache and muscle aches. But in some cases, it progresses to life-threatening encephalitis or meningitis. People age 50 and over are generally at a higher risk for severe symptoms.
Experts also say the virus tends to be at its worst in its second year in an area.
Last year was the first for West Nile to appear in areas west of the Continental Divide.
On Wednesday, New Mexico reported its first human West Nile case of 2004 in a San Juan County man. Mosquitoes from Pico Rivera, Calif., also tested positive for the virus in the first such laboratory results in Los Angeles County.
Weisbuch urged residents to protect themselves against mosquito bites and eliminate potential breeding sites for the insects around their property.
