3 diagnosed with West Nile virus in Louisiana

West Nile is transmitted by mosquitoes.

HAMMOND, Louisiana (CNN) -- Three Louisiana men have been diagnosed with West Nile virus, the state's epidemiologist said Thursday.

The men, one in his 50s, one in his 60s and one in his late 70s, are hospitalized with symptoms of encephalitis, said epidemiologist Raoult Rapard. He gave no condition report.

West Nile virus is a mosquito-borne disease that has spread rapidly since appearing in the New York metropolitan area just a few years ago. Birds infected by mosquito bites have carried it to other parts of the nation, where mosquitoes that bite them are infected and can spread the disease to humans.

EXTRA INFORMATION CDC: West Nile virus

Most people suffer no symptoms or experience only mild ones.

Last year the virus was reported in 18 states and the District of Columbia.