Health officials Tuesday confirmed the first human case of West Nile virus in Texas, further evidence of the disease's spread since it appeared in the United States three years ago.

Richard Hicks, 50, was admitted Friday to the Houston Veterans Affairs Medical Center with a fever and viral encephalitis, which causes swelling in the brain.

Hicks was beginning to recover, said Dr. Daniel Musher, the VA's head of infectious disease.

Previously, only birds and horses in Texas had tested positive for West Nile, which is spread by mosquitoes. Residents were encouraged to get rid of standing water and wear mosquito repellent and long-sleeve shirts when they are outdoors.

"We don't expect people to go sit in their homes from now until the end of September," Musher said.

The virus was identified in Uganda in 1937 and has spread to other continents, but until 1999 no cases had been confirmed in North America.

Since its detection in New York City in 1999, more than 150 people have been infected and 18 have died nationwide, according to the national Centers for Disease Control and Prevention.

Cases have been recorded in 31 states and the District of Columbia; the CDC added Texas, Oklahoma, Nebraska and North Dakota this year.