West Nile Virus

Transmission & Infection

The West Nile virus (WNV) is transmitted by the bite of mosquitoes that are infected with the virus. Mosquitoes become infected when they feed on infected birds. After an incubation period of 10 days to 2 weeks, infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. Following transmission by an infected mosquito, the virus multiplies in a person's bloodstream and crosses the blood-brain barrier to reach the brain.

The virus interferes with the normal central nervous system functioning and causes inflammation of the brain tissue (encephalitis). West Nile virus is not transmitted from person to person. For example, you cannot get the virus from touching or kissing a person who has the disease or from a health care worker who has treated someone with the disease. Similarly, there are also no known cases of an animal to person transmission of the virus.


The person infected with the virus will typically experience symptoms of the disease within 3 to 15 days after being bitten by an infected mosquito. Most infections are mild and symptoms include:

  • Body aches
  • Fever
  • Headache
  • Skin rash
  • Swollen lymph glands

More severe infection may be marked by:

  • Coma
  • Convulsions
  • Death (rare)
  • Disorientation
  • Headache
  • High fever
  • Muscle weakness
  • Paralysis
  • Stiffness
  • Stupor
  • Tremors

Fatality rates among people range from 3% to 15% and are highest among the elderly. Currently, there is no vaccine or specific treatment for West Nile virus. In more severe cases treatment requires intensive supportive therapy, such as:

  • Good nursing care
  • Hospitalization
  • Intravenous fluids
  • Prevention of secondary infections (pneumonia, urinary tract, etc.)
  • Respiratory support

Bird Testing

It is too early to speculate about the permanent establishment of West Nile virus in the United States. The testing of dead birds is part of the state's inter-agency surveillance system for WNV and other mosquito-borne viruses. If you observe an unusual change in the number of dead wild crows, ravens, jays, sparrows and other birds, you are encouraged to report birds that have been dead less than 48 hours to the Department of Health Services at 877-968-2473.

Health Services will send someone out to pick up the dead bird to be tested and inform you if it tests positive for WNV. There is no evidence that a person can get the virus from handling live or dead infected birds. However, avoid barehanded contact with all dead animals, including dead birds. It is a good idea to use gloves or double plastic bags to handle and dispose of the carcass.

Virus Background

The West Nile encephalitis virus (inflammation of the brain) is believed to have originated in Africa and is also found in West Asia and the Middle East. It is not known how long the West Nile virus has been in this country, but scientists at the Centers for Disease Control and Prevention believe that it has probably been in the United States since the early summer of 1999, and possibly earlier.

According to the Centers for Disease Control and Prevention, there have been 3 reported human disease cases for the West Nile Virus (WNV) in California during 2003. Of the total 9,122 cases reported in the United States for 2003, 6,251 cases (69%) were reported as West Nile Fever (milder disease), 2,707 (30%) were reported as West Nile meningitis or encephalitis (severe disease) and 164 (2%) were clinically unspecified. There are no reliable estimates available for the number of cases of the disease that occur worldwide.

This information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.

Contact Us

  1. Emergency Preparedness Committee

    Email the Committee

    30940 Hawthorne Boulevard
    Rancho Palos Verdes, CA 90275

    Phone: 310-544-5209