LOS ANGELES, June 22 (Xinhua) -- Health officials on Monday confirmed California's first human case of West Nile virus in 2009.

    The Los Angeles County Department of Public Health said the patient was a blood donor from the Antelope Valley near Los Angeles.

    The person, who was not identified, does not show any symptoms and is feeling well, the department's Sarah Kissell said.

    The patient's donated blood -- which was not used -- early this month. Health investigators are working to determine where the person may have contracted the virus.

    As of Friday, West Nile virus has been detected in Los Angeles County in five dead birds, two mosquito pools and three sentinel chickens, Kissell said.

    In past seasons, most of the infected birds and mosquitoes have been found in the San Fernando and San Gabriel valleys and East Los Angeles County areas.

    West Nile virus is spread to humans through the bite of an infected mosquito. Mosquitoes can become infected by biting a bird that carries the virus.

    The virus is not spread through person-to-person contact or directly from birds to humans. Symptoms include fever, muscle aches and skin rashes.

    "People should take precautions to avoid mosquitoes, as that is the primary way this disease is transmitted," said Dr. Jonathan Fielding, Los Angeles County's director of public health.

    "West Nile virus can appear anywhere in Los Angeles County or around the state, and we urge residents to get rid of pools of stagnant water around their homes where mosquitoes breed, and to use a repellant containing DEET or another approved repellent when outdoors in a mosquito-prone areas, especially around dawn or dusk," he said.

    To guard against West Nile virus, residents should wear light-colored long, loose clothing; stay indoors at dawn, sunset and early evening; apply mosquito repellent; and use mosquito netting when sleeping outdoors, health experts said.