First Symptomatic Human WNV Case Confirmed In LA County

Ruzanna Harutyunyan's picture

The Los Angeles County Health Officer has confirmed the first symptomatic human case of West Nile Virus (WNV) infection in Los Angeles County for the 2009 season. The case is a teenager, with pre-existing medical conditions, from the Antelope Valley who became symptomatic in mid-July. The individual has now recovered. Earlier this year, two individual blood donors, including one reported in June, tested positive for WNV, but did not show any symptoms (asymptomatic). The donated blood was not used.

"People should take precautions to avoid mosquitoes, as that is the primary way this disease is transmitted. Mosquitoes obtain the virus by feeding on infected wild birds," said Jonathan E. Fielding, MD, MPH, Director of Public Health and Health Officer. "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 mosquito-prone areas, especially around dawn or dusk."

As of August 5th, Public Health and the independent mosquito abatement districts have detected WNV in 38 dead birds, 6 mosquito pools, and 10 sentinel chickens. The Antelope Valley region of the county has shown the most WNV activity to date in 2009. In past seasons, most infected birds and positive mosquitoes have been found in the San Fernando Valley, San Gabriel Valley, and East Los Angeles County areas.

Exposure to West Nile Virus

WNV is spread from humans through the bite of an infected mosquito; mosquitoes can become infected by biting a bird that carries the virus. Most mosquitoes do not carry the virus and most people bitten by a mosquito have not been exposed to the virus. The virus is not spread through person-to-person contact, or directly from birds to humans.

In most case, people who are infected with West Nile Virus never become sick, or have only very mild symptoms that include fever, headache, nausea, body aches, and a mild skin rash. Symptoms of West Nile Virus could appear within three to 12 days after infection. Fortunately, fewer than one in 150 people who are bitten by an infected mosquito become severely ill, according to the Centers for Disease Control and Prevention (CDC). In these rare cases, the virus can cause encephalitis and death. The elderly are most at risk for severe cases of the disease. There is no specific treatment for West Nile Virus. However, individuals with severe symptoms may be hospitalized.

Preventive Measures


People can decrease their risk of infection by following these recommendations:

# Avoid mosquito-infested areas at dawn and dusk.

# Wear long-sleeved shirts and long pants whenever you are outdoors.

# Repellants containing DEET, picaridin, or oil of eucalyptus, when used as labeled, are effective defenses against mosquitoes.

# Check your window screens for holes.

# Do not allow water to collect and stagnate in old tires, flowerpots, swimming pools, birdbaths, pet bowls, or other containers. These are prime breeding grounds for mosquitoes.

# Clean and chlorinate swimming pools; drain water from pool covers.

# Stock garden ponds with goldfish or other mosquito- eating fish. These eat mosquito eggs and larvae.

# Empty and wash birdbaths and wading pools weekly.