5 Things to Know About West Nile Virus

Most people who experience these symptoms recover quickly, the CDC says, though fatigue and weakness can last for weeks, even months.

2. Older adults are at greater risk for serious illness

A small share of people (about 1 in 150) infected with the virus will develop more severe illness that affects the central nervous system. Complications can include encephalitis (inflammation of the brain) or meningitis (inflammation of the tissues surrounding the brain and spinal cord). According to the CDC, these complications can be marked by symptoms such as:

• High fever
• Headache
• Neck stiffness
• Stupor
• Disorientation
• Coma
• Tremors
• Convulsions
• Muscle weakness
• Vision loss
• Numbness and paralysis 

“Anytime somebody has high fever and a stiff neck, regardless of other situations going on, that’s a get-to-the-doctor-right-away type of situation,” Hopkins says. The same goes for seizures, weakness in the arms or legs, vision loss and numbness. “Those would all be things that need to be evaluated.”

Adults 60 and older are at greater risk (about 1 in 50) for developing a serious case of the disease if infected with the virus. “Their immune system is probably not going to respond quite as robustly as it would in younger people,” Hopkins says about the increased risk. “And I suspect it’s probably related to the fact that they [are more likely to] have more chronic medical conditions.”  

People with cancer, diabetes, hypertension and kidney disease — all diseases that become more common with age — are at greater risk for severe illness from West Nile virus, the CDC says; so are people who received organ transplants. 

Recovery from severe illness can take several weeks or months. In some people, the virus is fatal. 

3. Virus-carrying mosquitoes are common in the U.S. 

People often associate mosquito-borne illnesses with hot, tropical environments. That’s not the case with West Nile virus, Hopkins says. The primary transmitter of the virus is the common house mosquito (culex), which is found in urban and suburban areas.

It feeds from evening through morning, Hopkins says, and breeds in stagnant water. 

4. People are considered dead-end hosts  

The virus circulates between birds and mosquitoes, so if a person gets bitten by an infected mosquito, the chain of transmission stops there. “We’re kind of a dead-end host,” Hopkins says.

That’s because unlike birds, people “do not develop high enough levels of virus in their bloodstream and cannot pass the virus on to other biting mosquitoes,” the CDC explains.

In rare instances, the virus has been transmitted from person to person by blood transfusions, organ transplants or from mother to baby during pregnancy, delivery or breastfeeding. The virus is not spread through coughing, sneezing or touching (including touching live animals).

5. There are things you can do to help prevent an infection

There are no vaccines or medicines that can prevent illness from West Nile virus, but there are a few things you can do to lower your risk of infection.

• Use an insect repellent registered with the Environmental Protection Agency (EPA). 
• Wear long-sleeved shirts and pants.
• Wear clothing that’s been treated with permethrin.
• Eliminate or empty water-holding containers around your home, where mosquitoes can lay eggs. This includes buckets, toys, flowerpots and trash containers.

“I think for West Nile and most mosquito-related illnesses, the best protection is to prevent mosquito bites,” Lyssette Cardona, M.D., an infectious disease specialist for Cleveland Clinic Florida, said in a news statement. “And so at a personal level, if you’re going to travel, or if you’re around areas where there may be a lot of exposure to mosquito bites, just make sure you’re using the repellents that are safe for you, and or any specific netting and things like that if you’re camping.”

Editor’s note: This story, first published Aug. 27, 2024, has been updated to reflect new information.