What is the West Nile virus?
A virus is a tiny life form that can grow inside a
person or animal and may cause illness. West Nile virus is a type of virus
endemic in Africa, the Middle East, and parts of Asia. It is now found in the
United States, emerging in the summer of 2002.
How do you get West Nile virus?
The virus spreads by mosquitoes that become infected
when they bite birds carrying the virus. When an infected mosquito then bites a
person or animal, the virus is injected through the mosquito’s saliva into the
In addition, four novel (non-mosquito) modes of
transmission have been documented: through the placenta from mother to baby,
through breast-feeding, through the transplantation of infectious organs, and
through transfusion of infectious blood products.
What are the symptoms of West Nile virus?
In most cases, West Nile virus causes no illness or a
mild self limiting febrile illness. In some cases, the virus can cause a mild
illness called West Nile fever. The symptoms of West Nile fever resemble flu
symptoms and may include:
- Body aches
- Skin rash
- Swollen glands
Less frequently, West Nile virus can cause a more
serious illness, such as West Nile meningo-encephalitis – which is inflammation
of the brain – or meningitis – which is inflammation of the protective membrane
surrounding the brain and spinal cord. Symptoms of serious illness may include:
- High fever
- Stiff neck
- Decreased mental abilities
- Reduced alertness
- Involuntary movement of muscles (tremors or convulsions)
- Muscle weakness
In rare cases, West Nile virus can cause death.
How common is West Nile virus?
Many people get mosquito bites, but few get ill from
West Nile virus. Most people infected with the virus have very mild or no
symptoms. Less than 1 percent of people infected with West Nile virus get seriously ill.
Who is at risk for West Nile virus?
People who spend time outdoors in warm weather are at
risk for mosquito bites, but only a small percentage of mosquitoes carry the
West Nile virus. Among those that are bitten by infected mosquitoes, less than
30 percent will develop even mild symptoms. However, elderly people and those
with weakened immune systems may be less able to fight the virus and, therefore,
more likely to become ill from it.
Mosquitoes spread the virus, so the risk is greatest
when mosquitoes are active and reproducing, Mosquitoes are most active in warm
weather, and between dusk and dawn. In addition, female mosquitoes lay their
eggs in standing or very slow moving water. By avoiding these conditions, you
can reduce your risk of West Nile virus infection.
Blood products and solid organs transplanted from
infected individuals have been shown to transmit West Nile virus. However, the
nation’s blood supply is now screened for West Nile virus, and the number of
transfusion associated cases has declined significantly.
How do I know if I have West Nile virus?
Most symptoms of West Nile virus are mild and will go
away as your body fights the infection. However, see your doctor if you have
symptoms that don’t go away or if they concern you. The doctor may order a blood
test to look for evidence of the virus in your blood.
How is West Nile virus treated?
There is no specific treatment for West Nile virus.
Treatment plans focus on relieving any bothersome symptoms, such as body aches
or headache. People with severe illness may need to stay in the hospital to
receive supportive therapies—such as intravenous fluids and breathing
support—while their bodies work to fight the virus.
Is there a vaccine for West Nile virus?
There is currently no vaccine approved for use in
humans; however, researchers are actively seeking to develop a vaccine.
What is the outlook for people with West Nile virus?
Most people with West Nile virus recover fully with no complications.
Can West Nile virus be prevented?
The virus itself cannot be prevented, but you can take
steps to reduce your risk of mosquito bites. The US Centers for Disease and
Control offer these suggestions:
- Apply insect repellent with the ingredient DEET to your exposed skin
before going outdoors. (Use care when applying insect repellent to children.
Do not put repellent on their hands, and be careful to avoid their mouths and eyes.)
- Spray your clothing with insect repellent.
- Wear shoes and long-sleeve shirts and pants while outdoors, whenever possible
- If possible, stay indoors between dusk and dawn.
- Avoid activities in areas where mosquitoes are active and plentiful,
such as near standing water.
- Fix or install window and door screens to keep mosquitoes out of buildings and homes.
- Drain standing water that may collect in items such as flowerpots, pet
bowls, birdbaths, swimming pool covers, clogged rain gutters, buckets or barrels.
- Report dead or dying birds to your state health department.
Where can I learn more?
CDC Hotline: 1.800.232.4636
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 1/26/2010...#10939