What is the West Nile virus?

West Nile Virus is a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus which is also found in the United States. The virus can infect humans, birds, mosquitoes, horses and some other mammals.

How do people get West Nile virus?

People become infected with the West Nile virus through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected animals such as certain birds. You cannot get the West Nile virus by handling dead birds.

Can you get West Nile virus from another person?

No, West Nile virus is not transmitted from person to person.

What do I do if I find a dead bird?

The Department of Health is no longer studying dead birds but obtains records to monitor the approach of a West Nile Virus epidemic. If you find a dead bird, call 311 and request dead animal pick up with a specific location. If you are comfortable with properly disposing the bird, please follow this procedure:

•     Wear protective gloves or use a plastic bag as a glove
•     Place or wrap the dead bird in a plastic bag and tie the bag securely
•     Dispose of the bag in an outdoor trash receptacle
•     Wash your hands with soap and water

Remember, the West Nile virus is not transmitted directly from birds to humans.

What are the symptoms of West Nile virus?

Most people who become infected with the West Nile virus will not have any symptoms. Less than 1% of people who become infected with the West Nile virus will develop symptoms. Symptoms include fever, head and body aches and may include swollen glands and a skin rash on the body. The elderly and people living with weakened immune systems are at the highest risk for a more severe illness. A more severe infection may be marked by headache, high fever, neck stiffness, tremors, coma, weakness paralysis, and in vary rare cases, death.

What is West Nile encephalitis?

"Encephalitis" means 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. It is closely related to St. Louis encephalitis virus found in the United States.

How long has West Nile virus been in the US?

It is not known how long it has been in the US, but CDC scientists believe the virus has probably been in the eastern US since the early summer of 1999, possibly longer.

What is the basic transmission cycle?

Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. The virus is located in the mosquito's salivary glands. During blood feeding, the virus may be injected into an animal or a human, where it may multiply, and possibly cause illness.

If I live in an area where birds or mosquitoes with West Nile virus have been reported and a mosquito bites me, am I likely to get sick?

No. Even in areas where the virus is circulating, very few mosquitoes are infected with the virus. Even 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.

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 percentage of people who contract West Nile virus become severely ill? How many die?

Among those with severe illness due to West Nile virus, case-fatality rates range from 3% to 15% and are highest among the elderly. Less than 1% of persons infected with West Nile virus will develop severe illness.

If a person contracts West Nile virus, does that person develop a natural immunity to future infection by the virus?

It is assumed that immunity will be lifelong; however, it may wane in later years.

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. For adults, an effective repellent will contain 35% DEET (N,N-diethyl-meta-toluamide). DEET in high concentrations (greater than 35%) provides no additional protection. For children ages 2-6 years, an insect repellant which contains 10% DEET is recommended. For children less than age 2 years the use of insect repellant is not recommended.
• 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. 
• Install or repair window and door screens so that mosquitoes cannot get indoors.
• Note: Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites. 

I think I have symptoms of West Nile virus. What should I do?

Contact your health care provider if you have concerns about your health. If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should see your doctor immediately. For answers to health questions and clinical symptoms of the West Nile virus infection, please call the Department of Health Animal Disease Prevention Division at (202) 535-2323 Monday through Friday from 8:15 am to 4:45 pm.

How do health care providers test for West Nile virus?

Your health care provider will first take a medical history to assess your risk for West Nile virus. 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 provider will draw a blood sample and send it to a commercial or public health laboratory for confirmation.

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.

Where can I get more information about the West Nile virus?

• Contact the Department of Health’s Animal Disease Prevention Division at (202) 535-2323 for general information about the West Nile Virus and to request mosquito control treatment.
• Visit the Centers for Disease Control and Prevention’s West Nile virus website.