How Common Is West Nile Virus in the U.S.?

Fact checked by Nick BlackmerFact checked by Nick Blackmer

Key Takeaways

• West Nile virus cases are likely underreported because 80% of infections are asymptomatic or have mild symptoms that go unrecognized.

• Severe infections from West Nile virus are extremely rare, with less than 1% of cases leading to serious neurological diseases like encephalitis or meningitis.

• No vaccine or specific treatment for West Nile virus exists, so it's best to prevent mosquito bites through repellents and protective clothing.
  

Mosquito samples across the United States have tested positive for West Nile virus, but reported human infections remain low.

At least 72 people, mainly in Texas, Nebraska, Nevada, and Louisiana, have contracted West Nile virus this year, according to recent data from the Centers for Disease Control and Prevention (CDC). However, about 80% of people infected with the virus don’t experience symptoms and may not realize they’re infected, so the cases are likely underreported.

“Those that do have symptoms tend to be mild, so they may not seek care or get a diagnosis at all,” Kevin Steiner, MD, PhD, an infectious disease physician at The Ohio State University Wexner Medical Center, told Verywell.

West Nile virus has spread in the U.S. in the last 25 years. Mosquitoes can pass West Nile virus to humans after they bite infected birds. Infections typically spike in August and September but can happen any time of year.

“If a person notices that mosquitoes are still around, wherever that person might be located, there is still the potential for West Nile virus,” Steiner said.

Related: Are You a Mosquito Magnet? Here’s How to Make Yourself Less Prone to Mosquito Bites

Severe West Nile Virus Infections Are Extremely Rare

Most West Nile virus cases are asymptomatic, but some people can show mild symptoms, such as fever, headache, body aches, vomiting, diarrhea, joint pain, swollen lymph nodes, and rashes. These symptoms can occur up to two weeks after an infection and may last for a month.

Less than 1% of people infected with West Nile virus develop a serious neurological disease, such as encephalitis, inflammation in the brain, or meningitis, inflammation in the tissues around the brain and spinal cord. These severe cases can cause high fevers, seizures, paralysis, vision loss, coma, or death.

“Even if someone is bitten by an infected mosquito, the risk of developing severe disease is less than 1 in 100 and likely much, much lower in healthy adults,” Ross M. Boyce MD, MSc, an assistant professor of epidemiology at the University of North Carolina at Chapel Hill School of Medicine, told Verywell in an email.

Older adults and people who are immunocompromised may have a greater risk of developing a severe West Nile virus infection.

Although severe cases are rare, taking precautions is still crucial to avoiding an infection.

“The problem is that it only takes one bite from an infected mosquito to cause an infection. In some ways, you might think of it a bit like lightning. The odds of getting hit are very low, but most of us still take steps to minimize the risk in a thunderstorm,” Boyce said.

Related: Florida Will Release 750 Genetically Modified Mosquitoes to Stop Disease Spread

Avoid Mosquito Bites to Prevent West Nile Virus

There’s no West Nile vaccine for humans, so the best way to reduce your risk is to try to prevent mosquito bites. Heavy rain and flooding, like from Hurricane Beryl in Texas earlier this month, can create breeding grounds for mosquitoes.

“It’s been raining a lot and we’ve seen a boom in the mosquitoes right now. So any buckets of water, any tires that have water, just dispose of that, so the larvae cannot reproduce,” Rodrigo Hasbun, MD, MPH, a professor of infectious diseases at the University of Texas McGovern Medical School, told Verywell.

Mosquitoes can bite at any time of day, so wearing long sleeves and pants and using bug spray when going outside can also help reduce your risk. The Environmental Protection Agency has a tool to help you pick the right mosquito repellant for you, but most experts recommend using a product with DEET.

“It’s hot and humid right now, but try to cover up as much as possible with clothes and put DEET to prevent mosquito bites,” Hasbun said.

Related: Infected Mosquito Bite Symptoms and Treatment

There's No Treatment for West Nile Virus

Blood and cerebrospinal fluid tests can help diagnose West Nile virus, but one study suggests these tests are underutilized. Patients with meningitis or encephalitis who live in areas that have West Nile activities during peak mosquito season should be tested more frequently to ensure accurate diagnosis and treatment, according to the researchers.

“There’s no way to tell after any particular mosquito bite or any particular time outdoors, whether or not those mosquito bites may have had the virus,” Steiner said.

Last year, more than 1,800 people were hospitalized in the U.S. due to West Nile virus, but there are no medications for the disease. For severe illness, healthcare providers help manage complications with anti-seizure medications or respiratory support, Steiner said.

People with mild symptoms can manage their infection by staying hydrated, eating healthy foods, and taking over-the-counter pain or fever medications, he added.

“Sometimes people have swollen lymph nodes or a rash. Some might have some nausea or diarrhea, but most of these symptoms are pretty mild,” Steiner said. “People often don’t even think much of them at all, and they improve within a couple of days or a week or so, and people continue to go on about their normal lives.”

Read Next: Does Using Heat Actually Help With Itchy Mosquito Bites?

What This Means For You

Mosquitoes remain active year-round. Protect yourself by using insect repellent, wearing long sleeves, and eliminating standing water where mosquitoes breed. If you experience symptoms like fever or body aches after a mosquito bite, consult a healthcare provider.

Read the original article on Verywell Health.