West Nile virus
West Nile virus
West Nile virus is an infection transmitted by mosquitoes. If you become infected with West Nile virus, you may not experience any signs or symptoms or you may experience only minor ones, such as fever and mild headache. However, some people who become infected with West Nile virus develop a life-threatening illness that includes inflammation of the brain.
Mild signs and symptoms of a West Nile virus infection generally go away on their own. But severe signs and symptoms — such as a severe headache, disorientation or sudden weakness — require immediate attention.
Exposure to mosquitoes where West Nile virus exists increases your risk of getting West Nile virus. Protect yourself from mosquitoes by using mosquito repellent and wearing clothing that covers your skin to reduce your risk.
Most have no symptoms
Mild infection signs and symptoms
Serious infection signs and symptoms
Signs and symptoms of West Nile fever usually last a few days, but sign and symptoms of encephalitis or meningitis can linger for weeks, and certain neurological effects, such as muscle weakness, may be permanent.
When to see a doctor
Infection transmitted by mosquitoes
Most West Nile virus infections occur during warm weather, when mosquito populations are active. The incubation period — the period between when you're bitten by an infected mosquito and the appearance of signs and symptoms of the illness — ranges from three to 14 days.
West Nile virus is present in areas such as Africa, parts of Asia and the Middle East. It first appeared in the United States in the summer of 1999 and since then has been found in all 48 contiguous states.
Other possible routes of transmission
There have also been reports of possible transmission of the virus from mother to child during pregnancy or breast-feeding, but these have been rare and not conclusively confirmed.
West Nile virus transmission cycle
When a mosquito bites an infected bird, the virus enters the mosquito's bloodstream and eventually moves into the salivary glands. When an infected mosquito bites an animal or a human, the virus ...
Your overall risk of getting West Nile virus depends on these factors:
Risk of serious infection
Preparing for your appointment
If you experience signs and symptoms of a severe West Nile virus infection — such as a high fever, a severe headache, a stiff neck, disorientation or sudden muscle weakness — see your doctor right away or go to an urgent care center. If you are seriously ill, you may need to be hospitalized.
What you can do
What to expect from your doctor
Your doctor may take blood samples to be analyzed for West Nile virus antibodies. To be the most useful, these samples must be taken within the first eight days after symptoms appear. In some cases, your doctor may recommend other tests, as well. If necessary, your doctor may send you to a hospital for supportive therapy.
Tests and diagnosis
Your doctor can confirm the presence of West Nile virus in your body by analyzing a sample of your blood or the fluid surrounding your spinal cord (cerebrospinal fluid). If your doctor suspects a serious, West Nile virus-related illness such as meningitis or encephalitis, you may undergo a lumbar puncture or brain-imaging tests.
Treatments and drugs
There's no direct cure for encephalitis or meningitis, but you may need supportive therapy in a hospital with intravenous fluids and medicines to prevent other types of infections.
Your best bet for preventing West Nile virus and other mosquito-borne illnesses is to avoid exposure to mosquitoes and eliminate mosquito-breeding sites. To help control West Nile virus:
To reduce your own exposure to mosquitoes:
A vaccine is available to protect horses from West Nile virus. No vaccine is available for humans, but work to develop a human vaccine is under way.
Last Updated: 2010-06-26
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