What is West Nile Virus?

West Nile Virus (WNV) is a disease carried by mosquitoes that can be transmitted to humans and in serious cases can cause meningitis and encephalitis (inflammation of the brain).

How is it spread?

West Nile Virus was discovered in the West Nile District of Uganda in 1937 and has been detected in Africa, Europe, the Middle East and west and central Asia. First detected in the United States in 1999, WNV is transmitted to people and animals by infected mosquitoes. Mosquitoes become infected by biting a bird that carries the virus.

Is it easy to get?

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 by person-to-person contact or directly from birds to humans.

How bad is it?

Fewer than one out of 150 people who are bitten by an infected mosquito get severely ill, according to the Centers for Disease Control and Prevention (CDC). In most cases people who are infected never become sick or have only very mild symptoms for a few days.

Who is at risk?

In rare cases the virus may cause encephalitis and death. People over 50 years of age are most at risk for severe effects of the disease. Most of the serious U.S. cases have involved the elderly, according to the CDC. Only 1% of people bitten by infected mosquitoes became seriously ill.

What are the symptoms?

The incubation period is thought to range from 3 to 14 days. Most people who are infected with WNV have no symptoms. Of those that become ill, most symptoms are mild, such as fever, headache and body aches, mild rash and swollen lymph glands. Other mild symptoms might include loss of appetite, nausea or vomiting, fatigue, and eye pain. Symptoms generally last 3 to 6 days.

More severe symptoms might include a severe headache, high fever, stiff neck, confusion, seizures, muscle weakness or paralysis and loss of consciousness.

How is it treated?

There is no human vaccine currently available and no specific treatment for the West Nile Virus, but in a serious case, an individual may be hospitalized to ensure good supportive care.

Because most symptoms are mild, and similar to other viral diseases, the disease is underreported. It is thought that infected people develop a lifelong immunity to the disease.

For more information on West Nile virus, visit the Web site http://www.westnile.ca.gov/ and http://www.cdc.gov/ncidod/dvbid/westnile/