Mosquito samples in the Pittsburgh area recently tested positive for West Nile Virus, a mosquito-borne disease that causes about 2,000 diagnosed illnesses in people each year — a number the Centers for Disease Control says is an undercount.
The Allegheny County Health Department will spray for mosquitos on July 22 in several areas around the county, according to a press release from the department. They’ll spray when mosquitos carrying West Nile Virus are most likely to be active.
Here’s what to know.
What Parts of Allegheny County Will Be Sprayed for Mosquitos?
Allegheny County will treat Edgewood, Garfield, Homewood, Point Breeze, Regent Square and Wilkinsburg for mosquitos.
Mosquitos will be treated with Zenivex E20, one of the safest insecticides approved for use by the state department of environmental protection, according to Allegheny County Health Department.
The pesticide is sprayed in a way meant to reduce the amount used, according to the county health department, and it works only when it comes in contact with mosquitos. It also degrades rapidly in sunlight.
The pesticide will be sprayed from trucks on Wednesday, July 22 from 8 p.m. to 11 p.m. when the species of mosquitos carrying West Nile Virus are most active. If rain occurs, pesticide will be sprayed the following evening during the same hours.
Is West Nile Virus Common in the US?
West Nile Virus is most commonly spread to people through the bite of an infected mosquito during mosquito season, though it can also spread through organ transplantation, blood transfusion, exposure in a laboratory setting and from mother to baby during pregnancy, delivery or breastfeeding, the CDC said. Often, it doesn’t cause symptoms, or it results in minor illness. Rarely, the illness can develop into a neuroinvasive disease.
Every year, about 2,000 people in the United States are diagnosed with West Nile Virus, though many likely go undiagnosed because they do not have symptoms or attribute mild symptoms to other causes, according to the CDC.
So far in 2026, there has been one case of West Nile Virus in Allegheny County — Pennsylvania’s only reported case this year, according to the CDC.
Overall, there have been 81 reported cases of West Nile Virus infections in people in 18 states this summer as of July 21. Of those, 57 cases involved neuroinvasive disease, a more rare symptom type of West Nile Virus that involves neurological symptoms.
Most reported cases were in Arizona and Texas, with Arizona reporting 50 cases and Texas reporting seven. Other states reported one to two cases.
How to Prevent Mosquito Bites in Pittsburgh
There are precautions people can take to help prevent mosquito bites, including bites from the species carrying West Nile Virus.
“To deter mosquito bites, we encourage people to use insect repellent on exposed skin or to wear long sleeves and pants. Both methods are effective at reducing or eliminating the possibility of getting a mosquito bite,” said Allegheny County Health Department Vector Control Specialist Nicholas Baldauf.
He also added that stopping mosquitos from reproducing is an important part in reducing the county’s mosquito population.
“Mosquitoes can breed in as little as a half inch of stagnant water, so residents should pay close attention to potential breeding sites like stagnant water in tires, unused swimming pools, buckets, corrugated piping and clogged gutters,” Baldauf said.
If people see mosquito breeding sites on private or public properties, they should report those sites to Allegheny County Health Department’s Housing and Community Environment Program at 412-350-4046.
What Are the Symptoms of West Nile Virus? Is There Treatment?
West Nile Virus symptoms can appear two to 14 days after exposure, with an average incubation range of two to six days, according to the CDC. There’s the potential for a longer incubation period in immunocompromised people. About 80% of infections in people are subclinical or asymptomatic.
For those with symptoms, West Nile Virus can cause two types of illnesses: non-neuroinvasive disease and neuroinvasive disease. Non-neuroinvasive disease is more common, with symptoms such as:
Fever
Fatigue
Headache
Muscle pain
Joint pain
Transient maculopapular rash (red, bumpy skin)
Vomiting
Diarrhea
Neuroinvasive disease impacts less than 1% of people infected with West Nile Virus, with elderly individuals and immunocompromised people most at risk. It generally manifests as meningitis, encephalitis or acute flaccid myelitis.
There is no cure for West Nile Virus, and treatment is supportive, according to the CDC. No vaccine is available for use in people.
Finch Walker is the Pittsburgh Connect Reporter for the USA TODAY Network.
