West Nile Virus: 5 Things to Know

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West Nile virus is spread by mosquitoes to humans, horses and some other mammals. A mosquito gets the virus from biting an infected bird, and then passes the virus on when it feeds again. Most of the time the infection isn’t serious; it just causes mild flu-like symptoms, if it causes any symptoms at all. However, some people can experience life-threatening complications that can be fatal. Learn more West Nile virus information, including symptoms, treatment and prevention.

1. Anyone exposed to mosquitoes is at risk.

Because West Nile virus is spread by mosquitoes, anyone exposed to mosquitoes is at risk. West Nile virus isn’t spread through direct contact with other infected people. In very rare cases, the disease can be spread through organ transplant or blood transfusion. People over age 50 and those with compromised immune symptoms have a higher risk of developing more serious symptoms from West Nile.

West Nile transmission is most common during summer months; in warmer climates it can happen year round. West Nile virus has been found in all states in the contiguous United States, as well as Puerto Rico. Many other countries also present a higher risk of West Nile virus. These locations include countries in Europe, South America, Africa, the Middle East and western Asia.

2. Symptoms range from no symptoms to rare serious symptoms.

Most people with West Nile virus have no symptoms. For those who do experience symptoms, West Nile virus symptoms typically appear within a few days to two weeks after infection. These symptoms may last anywhere from a few days to several weeks, and they usually clear up on their own.

Only about 20% of healthy people will develop West Nile fever, which includes the flu-like symptoms of:

  • Fever
  • Swollen lymph glands

However, if the virus crosses the blood-brain barrier, it can cause more serious symptoms. Less than 1% of infected people develop these severe symptoms, which include:

  • Severe headache
  • Impaired consciousness and disorientation
  • Tremors or convulsions
  • Coma

These severe symptoms can look like those of other diseases, so it’s important to get immediate medical attention for an accurate diagnosis and appropriate treatment.

3. West Nile virus can cause serious complications.

While the disease usually isn’t fatal, some complications of West Nile virus can be life threatening. The virus can cause serious neurological problems, such as:

  • Meningitis, which is inflammation of the membranes that surround the brain and spinal cord
  • Meningoencephalitis, which is inflammation of both the brain and its surrounding membrane

Muscle weakness that results from these neurological symptoms can be permanent. Only about 1 in 150 people infected with West Nile virus will develop serious problems. However, these neurological problems are fatal for about 1 in 10 of people who develop them.

4. Treatment focuses on managing symptoms, preventing secondary infections.

Because West Nile is a viral infection, there’s no specific medical treatment for it. Most of the time, when symptoms are mild, people recover fully on their own with only symptom management. Someone with severe symptoms should seek medical attention right away; he or she may need hospitalization, IV fluids or help breathing. Medical care will also focus on preventing secondary infections such as pneumonia.

5. Avoid mosquito bites to prevent West Nile virus.

There’s no human vaccine for West Nile virus, but there are other ways to prevent infection, including avoiding mosquito bites. Ways to help prevent bites include:

  • Use insect repellent when outdoors, especially during summer months.
  • Wear long sleeves and pants while outdoors.
  • Stay indoors or use extra protection while outdoors between dusk and dawn, when mosquitoes are most active.
  • Make sure window and door screens are secure and in good condition.
  • Empty all containers with standing water, including gutters, flower pots, buckets and tire swings.
  • Change the water in bird baths and pet water dishes frequently.
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Sep 2
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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