On July 29th, the Southern Nevada Health District announced its first positive West Nile sample of the season, among mosquitoes found just south of Harry Reid International Airport.
No human cases have been reported so far, an encouraging sign to experts such as Vivek Raman, environmental health supervisor for the Southern Nevada Health District.
“We had about 25 human cases this time last year,” Raman said. He attributed it to natural ebbs and flows of West Nile disease spread, which starts in birds. “Either you have something in the bird population that creates immunity,” Raman said, “or the birds just die off, and then you go through a cycle then of it re-amplifying in that population to then spill over.”
So, that means 2025’s mosquito season has been milder than last year’s, which recorded a five-year high of mosquito-borne illness. Still, there’s other worrying news on the horizon. Researchers from UNLV’s Parasitology and Vector Biology Laboratory have found evidence of pesticide resistance among local mosquitoes.
Louisa Messenger is director of that lab, and also an assistant professor at UNLV’s School of Public Health. She said these pesticide-resistant mosquitoes are commonly found on and around golf courses in Summerlin and Henderson. And they’re appearing to survive pesticide concentrations 100 times higher than what is typically used, and for hours longer.
Messenger compares it to antibiotic resistance.
“If we continue to overuse a particular type of drug, or in this case particular types of pesticides or insecticides in the environment,” she said, “eventually it's inevitable that we will begin to select for resistance or increased tolerance of our mosquitoes in response to exposure to these chemicals.”
Since mosquitoes reproduce about every two weeks, that presents opportunities for pesticide resistant mutations to occur twice a month. This is a signal that Southern Nevada needs a more comprehensive regional abatement program, rather than allowing individual cities to create their own.
Messenger explained, “When insecticides are used sort of uncoordinated and unregulated fashions, if they're being used by private individuals and community groups, but there's no coordination or collaboration and sharing of information between partners — this is when you see resistance beginning to evolve.”
In the meantime, experts recommend removing any outside receptacles for standing water, keeping swimming pools clean and circulating, wearing insect repellents along with long sleeves and pants, and calling the Health District’s mosquito surveillance line at 702-759-1633 if you notice any mosquito activity in your neighborhood.
Guests: Louisa Messenger, assistant professor and director of the parasitology and vector biology laboratory, UNLV School of Public Health; Vivek Raman, environmental health supervisor, Southern Nevada Health District
