5 Things to Know About West Nile Virus

Older adults face a greater risk of complications from the mosquito-borne disease

Rachel Nania,

AARP

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En español

Published August 27, 2024

/ Updated August 30, 2024

mosquito illustration on a blue background

Photo Collage: AARP (Source: Shutterstock)

Cases of West Nile virus have been reported in the majority of U.S. states so far this year, and at least three deaths have been reported. The news may be leaving some people to wonder whether the mosquito-borne disease is yet another thing to add to their long list of health worries — especially while mosquito season is going strong.

There’s no need for people to be fearful, says Robert H. Hopkins Jr., M.D., medical director of the National Foundation for Infectious Diseases. That said, it’s a good idea to take a few precautions and to prevent mosquito bites if you can.

What is West Nile virus?

West Nile virus is the most common mosquito-borne disease in the continental U.S., according to the Centers for Disease Control and Prevention (CDC). As many as 9,862 cases are reported each year; the median is 2,205. The vast majority (94 percent) of these occur from July through September.

As of Aug. 27, there have been 289 reported cases this year, though that’s probably “a major underestimation,” Hopkins says, since many cases don’t cause symptoms and likely go undiagnosed.

Though its geographic reach is widespread — 33 states have reported cases in 2024 — the Great Plains and Western states are more likely to have a higher incidence of infections, the U.S. Department of Health and Human Services (HSS) says.

“And really, in the big scheme of things, mosquito-borne illnesses are likely to be more of a challenge for us as we continue to go forward as we see longer hot seasons,” Hopkins says.

Here are five things you should know about West Nile virus, including how to protect yourself while mosquito season persists.

1. Many infected people don’t experience symptoms

About 8 in 10 people who get bitten and infected by a mosquito will never know they have West Nile virus because they won’t develop symptoms, according to the CDC.

About 1 in 5 people who are infected do experience symptoms, which can include:

Headache
Body aches
Joint pains
Vomiting
Diarrhea
Rash

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. According to news reports, Fauci, 83, was likely infected from a mosquito bite he got in his backyard.

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 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.”

More mosquito-borne illnesses

Mosquitoes carry more than West Nile virus. Here are a few more diseases to pay attention to this season:

Dengue: U.S. health officials are monitoring a “higher than expected” number of dengue cases in the United States and popular travel destinations. An infection can cause mild, flu-like symptoms. However, in some people, a dengue infection can become severe — even life-threatening. Read more about dengue on AARP.org.
Eastern equine encephalitis: This rare but serious mosquito-borne disease is affecting some communities in Massachusetts, prompting spraying in certain areas. Only a few cases are reported in the United States each year; four have been reported in 2024, according to the CDC. The infection can result in neurological disease, and adults 50 and older are among the groups at highest risk for a severe infection. Read more about eastern equine encephalitis on CDC.gov.