Eight in 10 people don't even show signs of the virus.

By Amanda Gardner
August 23, 2019

As with most mosquito-borne illnesses, prime time for West Nile virus seems to be summer months—often starting in June and extending to the fall. And since it first arrived in the United States 20 years ago, West Nile virus has been infecting people across the country. 

But, what exactly is it—other than yet another scary-sounding disease that can be transmitted through a mosquito bite? Here's everything you need to know about West Nile virus during mosquito season, including it's signs, symptoms, and treatments—and how to avoid it altogether. 

What is West Nile virus—and what causes it?

West Nile virus is an infectious disease most commonly spread through mosquito bites. But humans are actually not a mosquito’s “preferred lunch” says William Schaffner, MD, an infectious diseases specialist at Vanderbilt University Medical Center in Nashville. “They prefer to bite birds. It’s not a virus that wants to make us sick. We are an incidental host.”

Although West Nile virus carried by mosquitoes infects and kills birds (especially crows and blue jays), it’s not possible for humans to catch it by handling dead birds. (That said, it’s still not a good idea to handle dead birds without gloves, according to the Centers for Disease Control and Prevention.)

When West Nile first came to the US in 1999, a few people did get it through blood transfusions and organ transplants, but that isn’t likely to happen today. “You could potentially get it through a blood transfusion but—and this is a big 'but'—our blood [supply] is screened for West Nile virus,” says Dawn Wesson, PhD, associate professor at Tulane University School of Public Health and Tropical Medicine in New Orleans.

There’s also an outside chance that pregnant and breastfeeding women infected with West Nile can pass the virus to their babies, but mothers should continue to breastfeed even if they become sick. There are so many benefits to breastfeeding that it outweighs the unknown risk of transmission, says Wesson.

The risk for transmitting West Nile during pregnancy seems to be low, as well. “There is some possibility if a woman is infected very close to delivery and she becomes very sick, the infant could become infected,” says Wesson. However, “it’s nothing like Zika infection.”

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What are the symptoms of West Nile virus?

Eighty percent of people who are infected with West Nile virus have no symptoms. In those who do develop symptoms—which accounts for about one in five people, per the CDC, West Nile virus in humans can cause fever, headache, body aches, joint pains, vomiting, diarrhea, or rash.

In those cases, symptoms usually occur three to 14 days after a person is bitten by an infected mosquito, and can last a few days up to several weeks. Even then, most people recover completely, but can have fatigue and weakness for a few months, per the CDC.

In rare cases—about one in 150 people infected with the virus—encephalitis (inflammation in the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord) can occur. 

Symptoms of these conditions can include a high fever, neck stiffness, headache, feeling disoriented, convulsions, paralysis, vision loss, weakness, and even a coma. People 60 years or older are more at risk, as are people whose immune systems have been compromised either because of another illness or because of medications they’re taking. About 10% of the people who develop these serious symptoms die.

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How is West Nile virus treated—and how it is prevented?

There is no vaccine for West Nile virus, although there are researchers working on developing one. There’s also no specific antiviral or other treatment for either West Nile fever or its more serious complications, per the CDC. 

“Basically, we’re treating aches and pains if you have them,” says Wesson. “If you’re hospitalized, we’re giving supportive care.” That can mean over-the-counter pain medicine for milder symptoms and, for people who are hospitalized, stronger pain medication and IV fluids.

As for how to prevent West Nile virus, the best way is to totally avoid getting bitten by mosquitos—and there are a number of ways that work.

“One of the most important things you can do [around your home] is look for any standing water, which might become a breeding site for mosquitoes,” says Dr. Schaffner. That means looking at the gutters on your house to make sure they’re draining properly, changing birdbath water frequently, and make sure any containers in your yard, including toys, are turned over so they don’t collect water. Pools usually aren’t a problem as long as they’re regularly maintained and the water keeps circulating rather than staying still.

When you’re outside in areas with mosquitoes, you can avoid bites by covering up with long sleeves and pants, especially in the mornings or evenings, when mosquitoes are most active. Use insect repellent on any exposed areas of skin. “I recommend DEET; for my own personal use, it’s been a very good option,” says Wesson. “Other approved repellents are oil of lemon eucalyptus and picaridin.”

“Some of these work better than others against specific mosquito species, and some work better on some people, so you may have to try more than one,” Wesson adds. “It also depends on how long you need to be protected, if it’s a multi-day camping trip or if it’s an hour or two.”

It’s okay to use DEET on children older than 2 months, according to the CDC. Oil of lemon eucalyptus should not be used on kids under 3. You can also protect kids of any age with long sleeves, and, if you’re using a stroller, cover the stroller with mosquito netting.

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