What is West Nile encephalitis?

Encephalitis is an inflammation of the brain and can be caused by viruses and bacteria, including viruses transmitted by mosquitoes. West Nile encephalitis is an infection of the brain caused by West Nile virus. 

Who gets West Nile encephalitis?

People who live in or traveled to areas where West Nile virus activity has been identified are at risk of getting West Nile encephalitis; persons older than 50 years of age have the highest risk of severe disease. Even in areas where mosquitoes do carry the virus, very few mosquitoes-much less than 1%-are infected. If the mosquito is infected, less than 1% of people who get bitten and become infected will get severely ill. The chances you will become severely ill from any one mosquito bite are extremely small.

How is West Nile virus spread?

West Nile virus is transmitted when mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then transmit West Nile virus to humans and animals. West Nile virus is not transmitted from person to person. There is no evidence that that a person can get the virus from handling live or dead infected birds. However, persons should avoid bare-handed contact when handling any dead animals and use gloves or double plastic bags.

Where is West Nile virus found?

West Nile virus has been commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East . It had not previously been documented in the Western Hemisphere until 1999. The continued expansion of West Nile virus in the United States indicates that it is permanently established in the Western Hemisphere . West Nile encephalitis cases occur primarily in the late summer or early fall. In the southern climates where temperatures are milder, West Nile virus can be transmitted year round.

What are the symptoms of West Nile encephalitis?

Most infections are mild, and symptoms include fever, headache, and body aches, occasionally with skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, rarely, death. Persons older than 50 years of age have the highest risk of severe disease.

How soon after infection do symptoms appear?

Usually, 3 to 15 days.

How is West Nile encephalitis diagnosed?

People who live in or traveled to areas where West Nile virus activity has been identified are at risk of getting West Nile encephalitis; persons older than 50 years of age have the highest risk of severe disease. If you are determined to be at high risk and have symptoms of West Nile encephalitis, your physician will draw a blood sample and send it to a commercial or public health laboratory for confirmation. If you have any of the above symptoms, contact your health care provider.

How is West Nile encephalitis treated?

There is no specific therapy. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, respiratory support (ventilator), prevention of secondary infections (pneumonia, urinary tract, etc.), and good nursing care.

Is a woman's pregnancy at risk if she gets West Nile encephalitis?

There is no documented evidence that a pregnancy is at risk due to infection with West Nile virus.

What proportion of people with severe illness due to West Nile virus die?

First, remember that less than 1% of people who get bitten by an infected mosquito become infected and get severely ill. Case-fatality rates range from 3% to 15% among those with severe illness due to West Nile virus, and are highest among the elderly.

Is there a vaccine against West Nile encephalitis?

No, but several companies are working towards developing a vaccine.

What can I do to reduce my risk of becoming infected with West Nile virus?

• Stay indoors at dawn, dusk, and in the early evening.
• Wear long-sleeved shirts and long pants whenever you are outdoors.
• Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing.
• Apply insect repellent sparingly to exposed skin. An effective repellent will contain 35% DEET (N,N-diethyl-meta-toluamide). DEET in high concentrations (greater than 35%) provides no additional protection.
• Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children.
• Whenever you use an insecticide or insect repellent, be sure to read and follow the manufacturer's DIRECTIONS FOR USE, as printed on the product.
• Note: Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.