If there is one time of year to break out the bug spray, it’s Labor Day weekend.
“This is the prime time — the last week of August and the first week of September — when West Nile usually peaks nationally,” said Dr. Erin Staples, a mosquito expert and medical epidemiologist at the Centers for Disease Control and Prevention. “People need to be using their insect repellent right now.”
Mosquito-borne viruses are making their rounds across the country, sometimes with devastating effects. According to the CDC, 289 cases of West Nile virus have been logged so far in 2024. A majority of those patients, 195, developed severe neurological problems like inflammation of the brain or paralysis. At least 18 died.
“This is the time of year when cases of West Nile virus rapidly increase,” Staples said. While it’s too early in the season to compare this year with others, she said, “some areas like Texas and New York City are seeing a lot of activity.”
Another virus spread by mosquitoes, Eastern equine encephalitis, is less widespread but deadlier. This month, a 41-year-old New Hampshire man without any underlying medical problems died of EEE. “It doesn’t matter how old you are,” Staples said. EEE “can, unfortunately, kill.” A handful of other cases of EEE have been detected in Massachusetts, New Jersey, Vermont and Wisconsin.
Among people with severe symptoms related to EEE, nearly a third will die. The mortality rate among people with similarly serious West Nile virus disease hovers at about 10%.
What are symptoms and warning signs?
The good news is that the vast majority of people who are infected by West Nile or EEE never know it because they have no symptoms. Symptoms for both of the viruses, which can begin anywhere from three days to two weeks after the mosquito bite, include:
- Fever
- Headache
- Fatigue
- Nausea
The viruses become a serious problem if they get into the central nervous system, affecting the brain or spinal cord.
A sure sign that warrants an immediate call to 911 is an unexplained altered mental state or confusion, said Dr. Waleed Javaid, director of Infection Control and Prevention at Mount Sinai Downtown in New York City.
“If a person starts getting confused while they are ill with flu-like symptoms, that should trigger a trip to the hospital or urgent care,” Javaid said.
How are mosquito-borne illnesses diagnosed?
It’s virtually impossible for doctors to diagnose a mosquito-borne illness on symptoms alone.
“West Nile and Eastern equine encephalitis can cause the same presentation,” Staples said. “The clinician looking at them is not going to know” the difference without testing.
Blood tests are most commonly used to make an official diagnosis. If a person has severe neurologic symptoms, doctors may test the patient’s fluid around the brain through a spinal tap.
The reason tests are usually done is not necessarily to help the patient; it’s to inform public health officials about where mosquitoes are spreading potentially deadly viruses.
There is no specific treatment for either EEE or West Nile. People who are sick enough to be hospitalized are given supportive care to deal with severe symptoms.
“All we really can do is keep them hydrated, keep their fevers down and make sure they don’t have respiratory failure,” said epidemiologist Dr. W. Ian Lipkin, director of the Center for Infection and Immunity at the Columbia University Mailman School of Public Health in New York City.
Is 2024 a bad year for mosquitoes?
This is the time of year most of the bloodsuckers like to feast. While it's not yet clear if 2024 will be an unusually active year for mosquito-borne viruses, experts say it’s likely cases will increase in the coming years.
Climate change is leading to hotter temperatures and rainier seasons — perfect breeding grounds for mosquitoes.
The future may bring more EEE and West Nile infections, said Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University Medical Center in Nashville, Tennessee.
“With climate change you get abundant mosquitoes,” he said. Moreover, “the increased warmth allows the virus to replicate more quickly in the mosquito which makes it more likely for it to transmit the virus when it bites you.”
How to prevent mosquito bites
The best way to avoid mosquito bites is to use bug sprays with DEET. The CDC also recommends Picaridin (known as KBR 3023 and icaridin outside the U.S.).
The sprays won’t kill the bugs, but they are effective in keeping them at bay.
- Dress in loose-fitting long sleeves and long pants.
- Pour out any standing water in bird baths, dog bowls, flowerpots and toys left outside.
Erika Edwards is a health and medical news writer and reporter for NBC News and "TODAY."
Linda Carroll
Linda Carroll is a regular health contributor to NBC News. She is coauthor of "The Concussion Crisis: Anatomy of a Silent Epidemic" and "Out of the Clouds: The Unlikely Horseman and the Unwanted Colt Who Conquered the Sport of Kings."
