West Nile Virus

West Nile virus is a mosquito-borne virus that can cause a range of symptoms that vary in severity in humans. In the United States, birds appear to be the major carriers of the disease. It has been found in other animals such as horses, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits.

Mosquitoes ingest the virus when they feed on the blood of infected birds or other animals. The mosquitoes pass the virus to people when they bite them. There have been rare instances of transmission of the disease in other ways.

West Nile virus is commonly found in Africa, West Asia, and the Middle East. The first case diagnosed in the United States was in August 1999 in New York City. It is not known how the virus got into the United States. Since that time it has spread widely throughout the United States. At the end of 2002, only Oregon, Nevada, Utah, and Arizona appeared free of the disease but that is expected to change soon.

Most people with the virus have little or no symptoms and the symptoms usually last a few days. Symptoms appear 3 to 15 days after being bitten by an infected mosquito. Less than 1 percent of those infected will develop serious illness such as encephalitis, inflammation of the brain, or meningitis, inflammation of the membranes and fluid surrounding the brain and spinal cord. A smaller number of cases have been fatal. The risk of severe infection is greatest for people who are over age 50 or who have a weakened immune system.

Common signs and symptoms of West Nile virus infection include:

fever
headache
muscle aches
backache
skin rash and
swollen lymph glands

Severe symptoms, which involve the brain, include:

severe headache
stiff neck
stupor
disorientation
coma
tremors
convulsions
muscle weakness and
paralysis

The risk of West Nile virus is seasonal in the northern states and begins in the spring with the peak time for infection in mid to late August. In the milder southern climates, transmission may occur year-round.

There is no specific medication to treat West Nile virus and no vaccine is yet available to prevent it for humans. There is a vaccine for horses. See your healthcare provider as soon as possible if you experience severe symptoms during mosquito season that might suggest West Nile virus. Your healthcare provider can confirm the virus through a blood test. Other tests can detect whether West Nile virus has caused encephalitis or meningitis.

Efforts to prevent the spread of the disease are being made by state and federal governments, especially in eliminating mosquito-breeding sites. Take precautions to avoid mosquito exposure by eliminating standing water in yards, unclogging roof gutters, emptying unused swimming pools, changing bird bath water weekly, and observing for sick or dying birds and reporting that to the local health department.

Avoid unnecessary outdoor activity during peak mosquito biting times, usually early evening, dusk to dawn. Protect yourself from mosquito bites by wearing long-sleeved shirts, long pants, and socks when going into mosquito-infested areas, spraying clothing with insect repellent, and applying insect repellant that contains 20 to 30 percent DEET to certain exposed areas. Caution: Use insect repellent sparingly and avoid concentrations of more than 30 percent. Do not apply this type of insect repellent to children less than 3 years old and always follow the manufacturer's directions for use.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

HIL File INFE4708.RF2 VRS# 4708 Data Version 7.0