West Nile virus
West Nile virus
West Nile infection is caused by a virus transmitted by mosquitoes. Most people infected with West Nile virus don't experience any signs or symptoms, or 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, fever, disorientation or sudden weakness — require immediate attention.
Exposure to mosquitoes where West Nile virus exists increases your risk of getting West Nile virus infection. Protect yourself from mosquitoes by using mosquito repellent and wearing clothing that covers your skin to reduce your risk.
Most have no signs or symptoms
Mild infection signs and symptoms
Serious infection signs and symptoms
Signs and symptoms of West Nile fever usually last a few days, but signs 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 its salivary glands. When an infected mosquito bites an animal or a human (host), the ...
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're 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. 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 or a West Nile-related illness, such as meningitis or encephalitis, by performing one of the following tests:
Treatments and drugs
Use caution when giving aspirin to children or teenagers. Though aspirin is approved for use in children older than age 2, children and teenagers recovering from chickenpox or flu-like symptoms should never take aspirin. This is because aspirin has been linked to Reye's syndrome, a rare but potentially life-threatening condition, in such children.
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: 2012-12-18
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