The West Nile virus is transmitted by mosquitoes to birds, various animals, and humans. Most persons infected with this virus show no symptoms, although occasional infections can result in serious illness and even death.
West Nile virus has been commonly found in humans, birds, and other animals in Africa, Eastern Europe, Western Asia, and the Middle East, but until 1999 had not previously been documented in the Western Hemisphere. The U.S. viral strain is most closely related genetically to strains found in the Middle East.
Most people infected with this virus do not have any symptoms. Some people experience a mild illness characterized by slight fever, headache, body aches, skin rash, and swollen lymph nodes. More severe illness can include encephalitis (inflammation of the brain) and is marked by a rapid onset of a high fever, head and body aches, neck stiffness, muscle weakness, disorientation, coma, tremors, convulsions, and in the most severe cases, death.
Symptoms usually appear 3 to 15 days after exposure.
There is no evidence that pregnant women are at increased risk due to West Nile virus infection.
The West Nile virus, like most mosquito borne viruses, is found in wild and domestic birds. When a mosquito feeds on an infected bird, it can pick up the virus and transmit it to other, non infected birds. Occasionally, infective mosquitoes will feed on mammals such as horses, dogs, cats, and humans, and transmit the virus to them.
No, even in areas where mosquitoes do carry the virus, 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.
There is no evidence that a person can get the virus from handling live or dead infected birds. However, persons should avoid barehanded contact with any dead animals and use gloves or double plastic bags to place the carcass in a garbage can.
West Nile virus infection 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.
It is not necessary to limit any outdoor activities. However, you can and should try to reduce your risk of being bitten by mosquitoes. Mosquitoes are most active at dawn and dusk. Reducing the mosquito population around your home and property can be accomplished by eliminating standing water:
Hunters should follow the usual precautions when handling wild animals. They should wear gloves when handling and cleaning animals to prevent blood exposure to bare hands and meat should be cooked thoroughly. If hunters anticipate being exposed to mosquitoes, they should apply insect repellents to clothing and skin according to label instructions.
If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headache, you should see your health care provider immediately. Your health care provider will assess your risk for West Nile virus infection. If you are determined to be at high risk, your provider will draw a blood sample and send it to a laboratory for confirmation.
There currently is not a vaccine for West Nile , but several companies are working towards developing a vaccine. While there is no current treatment for the virus, patients are treated in a supportive care role. For example, if the patient has a high fever, then they would receive antibiotics based on their physician's recommendations.
There is no specific treatment for viral infections, other than to treat the symptoms and provide supportive care. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids and nutrition, respiratory support, prevention of secondary infections, and good nursing care. Elderly persons are at highest risk for developing severe illness due to West Nile viral infection, so these individuals should promptly seek medical care if infection is suspected.
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