Deaths due to West Nile virus are on the rise nationally and are at record highs in states like Arizona, where cases of the disease should be rare because conditions are generally too dry to support a large mosquito population, since without water, the little blood sucking bugs can’t reproduce.
By late September there were 123 cases of symptomatic West Nile in Arizona and four deaths, according to the Arizona Department of Health Services. Nationally, as of Sept. 21, the Centers for Disease Control and Prevention reported a total of 479 cases of West Nile virus disease in people. Of these, 315 (66%) were classified as severe, meaning the virus had invaded the nerves in the spine and/or brain causing conditions such as meningitis or encephalitis (inflammation of the brain).
Experts say, wherever you live, the best way to protect against infection with the virus is to avoid being bitten by mosquitos.
Even if you are bitten by a virus carrying mosquito, the vast majority of people infected with West Nile will have such a mild case they won’t even know they’ve had the disease, said Dr. Timothy Brewer, a professor of medicine in the division of infectious diseases, at the David Geffen School of Medicine at the University of California, Los Angeles, and a professor of epidemiology at the UCLA Fielding School of Public Health.
Studies suggest that about 1 in 5 people infected with the virus will have symptoms, Brewer said. Those symptoms can include fever, muscle pain and fatigue and sometimes a temporary weakness or paralysis affecting one side of the face. One in 150 will develop severe disease in which nerve cells are attacked by the virus.
Among those with a severe case of West Nile, the risk of death is about 1 in 10, Brewer said.
West Nile disease in humans was first detected in Uganda (hence the virus’ name) in the 1930s and first appeared in the U.S. in the late 1990s.
Mosquitos get the virus from birds and then pass it along to humans, said Dr. Noreen Hynes, director of the Geographic Medicine Center in the division of infectious diseases at Johns Hopkins Medicine, an associate professor of medicine at the Johns Hopkins University School of Medicine and a faculty member in the department of international health at the Johns Hopkins Bloomberg School of Public Health.
The vast majority of cases are spread by Culex mosquitoes which are native to the U.S. and are most often looking to suck human blood from dusk until dawn. Imported blood suckers, such as the Aedes aegypti, which are more known for spreading diseases like dengue fever and Zika, sometimes also spread West Nile, Hynes said.
People aged 60 and older and those with compromised immune systems are the most likely to develop symptomatic infections, including severe ones, Hynes said, adding that currently there is no vaccine or antiviral drug to treat an infection. “So you can only give supportive care to someone with severe disease,” she said.
How to avoid mosquito bites:
All of that makes finding ways to avoid being bitten by a mosquito imperative.
The first thing to do, Hynes said, is to get rid of all standing water near your home. “If water has collected in buckets, the cups under flower pots, your dog’s outdoor water dish, you need to empty them out so mosquitos don’t lay their eggs in them and replicate close to home,” she added. “The number one priority is getting rid of standing water.”
After you’ve dealt with the standing water, “repellents become very important,” Hynes said. “Right now we are in the season for West Nile so you should remember two things. First, they can bite through your clothing so you should pretreat your clothes with an EPA-approved insect repellant, such as permethrin, which gets embedded in the clothing fibers and stays in them for up to six weeks or six machine washings.”
Your next priority is to apply repellant — either permethrin or picaridin — to your skin. “Make sure all exposed skin is covered and if you sweat a lot make sure you apply it every two hours,” Hynes said. If you go swimming put it back on when you’re done swimming.”
Hynes also recommends wearing light colors. That’s because “mosquitos aren’t as drawn to light colors,” she said.
The good news, Hynes said, is that children born after the 1990s probably won’t have to worry about getting severe cases of West Nile Virus when they are seniors because they most likely will have already gotten infected and developed immunity to the virus.
If you’re wondering about those high numbers of cases in Arizona, Brewer said that research has correlated cases with the people’s socioeconomic status: Apparently wealthy people were more likely to get the virus than poorer folk. A possible explanation is that wealthy people might be irrigating lawns (which could lead to big puddles) or maintaining ornamental ponds, both possible mosquito-friendly habitats.