West Nile Virus

Symptoms and Care

What is West Nile virus?

West Nile virus (WNV) is a mosquito-borne disease that can infect humans, birds, horses and other mammals. In most humans, WNV infection can cause a mild flu-like illness, or may cause no symptoms at all. However in some cases, particularly among the elderly, it can cause severe neurological diseases such as encephalitis or meningitis. West Nile virus first appeared in North America in New York City in 1999. Since then, the virus has spread across the continental United States (visit www.cdc.gov for more information on WNV nationally).

How is West Nile virus spread?

West Nile virus is predominantly spread to humans by the bite of an infected mosquito. In 2002 other methods of human transmission were discovered. It has now been shown that West Nile virus can be transmitted to humans who receive infected organs through transplantation, or who receive transfusions of infected blood or blood products. Also, in 2002 there was one case of transmission from a pregnant woman to her fetus and one mother-to-child transmission through breast milk. West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected.

What are the symptoms of West Nile virus?

Most people who are infected with West Nile virus either have no symptoms or experience mild illness such as fever, headache and body aches before fully recovering. Some persons may also develop a mild rash or swollen lymph glands. In some individuals, particularly the elderly, West Nile virus can cause serious disease that affects brain and spinal tissue. Severe illness may include encephalitis (inflammation of the brain), meningitis (inflammation of the membrane around the brain and spinal cord), and acute flaccid paralysis (a polio-like syndrome in which muscles become very weak or paralyzed). Symptoms may include: headache, high fever, stiff neck, confusion, coma, tremors, convulsions, and muscle weakness or paralysis. At its most serious, West Nile virus can cause permanent neurological damage and death.

Can you get West Nile virus from another person?

West Nile virus is spread to humans predominantly by the bite of an infected mosquito. In 2002 other methods of human transmission were discovered. It has now been shown that West Nile virus can be transmitted to humans who receive infected organs through transplantation, or who receive transfusions of infected blood or blood products. Also, in 2002 there was one case of transmission from a pregnant woman to her fetus and one mother-to-child transmission through breast milk. West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected.

How long does it take to get sick if bitten by an infected mosquito?

Most people who are infected with West Nile virus have no symptoms or experience only mild illness. If illness does occur, symptoms generally appear within 3 to15 days of being bitten by an infected mosquito.

I've gotten a mosquito bite. Should I be tested for West Nile virus?

The proportion of mosquitoes infected with West Nile virus is very small. However, if you develop symptoms such as high fever, confusion, muscle weakness, severe headaches, and stiff neck or if your eyes become sensitive to light, you should see a doctor.

How is West Nile Virus encephalitis treated?

There is no specific treatment for West Nile virus. Most humans who become infected will get better on their own. In more severe cases, intensive supportive therapy is indicated, i.e., hospitalization, intravenous (IV) fluids and nutrition, airway management, ventilatory support (ventilator) if needed, prevention of secondary infections and proper nursing care.

Is there a vaccine for West Nile virus?

There is currently no vaccine for West Nile virus, but several companies are working towards developing one.

What proportion of people die when infected with West Nile virus?

Fewer than 1% of people infected with West Nile virus develop encephalitis, and among those hospitalized with West Nile encephalitis, the case fatality rate ranges from 10% to 15%. Therefore, fewer than 1 in 1,000 people infected with West Nile virus die. Individuals over the age of 65 are at greatest risk for the severe complications of WNV.

For more information on West Nile virus, call 311 or visit nyc.gov/health/wnv.