AARP Hearing Center
5 Things to Know About West Nile Virus
Cases of the mosquito-borne disease are surging in the U.S., and older adults face a greater risk of complications if infected
Photo Collage: AARP (Source: Shutterstock)
Key takeaways
- U.S. West Nile cases are at their highest early-season level since 2004, with 48 reported by June 30 and most classified as severe.
- Most infections cause no symptoms, but older adults face a higher risk of serious neurological illness if infected.
- Prevention focuses on avoiding mosquito bites, especially at dusk and dawn, since there’s no vaccine or treatment.
The U.S. is seeing its highest number of West Nile virus cases for this point in the season since 2004. At least 48 cases have been reported as of June 30, the Centers for Disease Control and Prevention (CDC) announced, and at least 38 of them have been cases of severe neuroinvasive disease, affecting the brain or nervous system.
Since 2004, an average of 10 human disease cases has been reported by the end of June. The current surge, health officials said, “is driven by early circulation of the virus, with 23 states reporting West Nile virus activity — also the highest number recorded over the last 10 years.”
More Ways to Benefit
- Related Benefit 1
- Related Benefit 2
- Related Benefit 3
- Related Benefit 4
- Related Benefit 5
Reports of West Nile virus may leave some people wondering whether the mosquito-borne illness is yet another health concern to add to their long list, especially with mosquito season expected to stretch into the fall.
There’s no need for people to be fearful, Dr. Robert H. Hopkins Jr., medical director of the National Foundation for Infectious Diseases, told AARP. That said, health officials are urging people to take precautions this summer to protect themselves from mosquito bites.
“These findings serve as an important reminder that mosquito season is well underway,” said CDC medical epidemiologist Dr. Erin Staples.
What is West Nile virus?
West Nile virus is the most common mosquito-borne disease in the continental U.S., according to the CDC. As many as 9,862 cases are reported each year, although the median is 2,205. The vast majority (94 percent) of these occur from July through September.
Hopkins says cases reported to the CDC are likely “a major underestimation,” since many cases don’t cause symptoms and likely go undiagnosed.
Although its geographic reach is widespread, the Great Plains and western states are more likely to have higher infection rates, the U.S. Department of Health and Human Services 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 during mosquito season.
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 have received organ transplants.
Recovery from severe illness can take several weeks or months. In some people, the virus is fatal.
More mosquito-borne illnesses
Mosquitoes carry more than West Nile virus. Here are a couple of more diseases to pay attention to this season:
- Dengue: A dengue infection can cause mild, flu-like symptoms, but in some people, it can become severe — even life-threatening. Read more about dengue on AARP.org.
- Eastern equine encephalitis: Only a few cases of this rare but serious mosquito-borne disease are reported in the United States each year. 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.
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 generally don't carry West Nile virus.
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. You can take steps to avoid 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).
- Avoid being outside between dusk and dawn, when the mosquitoes that spread West Nile virus are most active.
- 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.
- Use screens on windows and doors or air conditioning.
“I think for West Nile and most mosquito-related illnesses, the best protection is to prevent mosquito bites,” Dr. Lyssette Cardona, an infectious disease specialist for Cleveland Clinic Florida, said. “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.
AARP Membership
Join AARP for only $15 per year with automatic renewal. Get instant access to members-only products and hundreds of benefits, a free second membership, and a subscription to AARP The Magazine.
More From AARP
The Blood Type Mosquitoes Crave
4 surprising reasons mosquitoes attack you
Parasite Illness Spreads in U.S.
Older adults should know the symptoms and when to ask about stool testing
Smart Guide to Reducing Inflammation
31 ways to tamp down the chronic condition