West Nile Virus

In the United States, West Nile virus is the most common cause of mosquito-borne illness. While a small number of people become seriously ill from this condition, most people have no symptoms and recover completely.

What are the Symptoms of West Nile Virus?

About one in five people with West Nile virus have symptoms that are similar to those of the flu. They begin a few days or up to several weeks after the mosquito bite and are often mild.  

West Nile virus symptoms can include:

• Fever
• Headache
• Nausea or vomiting
• Diarrhea
• Muscle aches
• Swollen lymph nodes

What Happens With Severe West Nile Virus?

In a small number of people—about one in 150—the West Nile virus enters the brain and causes a serious inflammation called encephalitis. This virus can also cause meningitis, which is inflammation of the membranes around the brain and spinal cord. This is more likely to happen in people who are older or have weakened immune systems.

People with a serious West Nile virus infection can have:

• Severe headache
• Stiff neck
• High fever
• Seizures
• Confusion
• Muscle weakness, partial paralysis or tremors

These symptoms can indicate a life-threatening illness and people experiencing them should get medical help immediately.

How is West Nile Virus Diagnosed and Treated?

If you have symptoms of West Nile virus infection, your doctor will ask if a mosquito has bitten you recently. He or she will do a physical exam and order blood tests to confirm the diagnosis. In some cases, a spinal tap is done to get a sample of spinal fluid, and people with severe symptoms may have an imaging test to check for inflammation of the brain.

There is no medicine or treatment for West Nile virus infections. People with a mild illness can treat their symptoms with an over-the-counter pain reliever or anti-inflammatory medicine. Mild symptoms usually go away on their own in a few days.

Severe West Nile virus infections may require hospitalization. Treatment in the hospital can include IV fluids, help with breathing and other therapies.

How Can People Avoid West Nile Virus?

West Nile virus can’t be transmitted from person to person or from infected animals to people. The best way to protect yourself from this infection is to avoid mosquito bites.

These steps can help:

• Use insect repellent before you go outside. Apply it after sunscreen.
• Get rid of any standing water on your property, or empty and scrub any containers weekly. Water in tires, buckets, planters, birdbaths and other areas creates breeding grounds for mosquitoes.
• Keep mosquitoes out of your house with window screens.
• Try to stay indoors during the early evening and early morning hours when mosquitoes are most active.
• If you are outside when mosquitoes are present, wear long sleeves and long pants.