Maricopa County has led the nation in West Nile virus cases this year, as of the end of July, according to the Centers for Disease Control and Prevention.
Of the 71 reported infections in Arizona, the state's most populous county was home to 54 of them as of Aug. 4, the CDC reported.
There are safeguards to reduce the risk of contracting West Nile virus through mosquito bites.
Five people in Maricopa County have died from the virus, which is transmitted by mosquitoes. The first reported death related to West Nile virus was in June.
Cases of West Nile virus in the county between Jan. 1 and July 31 have risen nearly 63% compared to the same period in 2025. Last year, in total, seven people died, and 56 people were infected.
Here's what to do to avoid infection.
What is West Nile virus?
West Nile virus is a disease most commonly spread to humans by mosquito bites. It is not transmitted through the air or by touching animals.
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Spikes in infection rates nationwide typically occur in late August to early September but last through all of mosquito season, the CDC said.
About 80% of infected people don't develop symptoms.
What are the symptoms of West Nile virus?
Symptoms typically begin two to six days after being bitten by an infected mosquito, but it can take up to 14 days for symptoms to show.
About 20% of people who are infected develop flu-like symptoms, such as fever, headache, body ache, vomiting, diarrhea or rash, according to the CDC. Most people with mild illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.
Less than 1% of people infected develop severe illness that affects the central nervous system, requires hospitalization or results in death, the CDC said. Those illnesses are usually encephalitis, inflammation of the brain, or meningitis, inflammation of the membranes around the brain and spinal cord.
Symptoms of severe illness include: High fever, headaches, neck stiffness, stupor, disorientation, coma, tremors or convulsions, muscle weakness, vision loss, numbness and paralysis.
About 10% of people who develop severe illness affecting the central nervous system die, according to CDC.
Who is most at risk for West Nile virus?
Anyone who lives in a hotspot is at risk for West Nile virus.
The risk of severe illness increases with age, certain chronic medical conditions or a weakened immune system.
Where are the hotspots for West Nile virus?
According to the Arizona Department of Health Services, about 100 human cases of West Nile virus are reported each year statewide. The virus has been seen in humans in Coconino, Maricopa, Pima and Pinal counties, while La Paz and Yuma counties reported infections in animals.
Maricopa County has reported 54 infections, Pima County has reported 15 and Pinal and Coconino counties each have reported one infection to the CDC.
All states bordering Arizona have also reported at least one case of West Nile virus. Nationwide, Texas has seen 18 cases, and California has reported 11.
How do I protect myself from West Nile virus?
There are no vaccines or medicines to prevent West Nile infection. The best way to protect yourself is to prevent mosquito bites, according to the CDC.
You can:
• Use an insect repellent
• Wear long, loose-fitting shirts and pants so it is harder for mosquitoes to bite your skin
• Avoid being outside between dusk and dawn when the mosquitoes that spread West Nile virus are most active
• Use screens on windows and doors to keep mosquitoes outside
Mosquitoes tend to congregate near still water, and recent heightened storm activity can create the "perfect" breeding ground for the bug, the Arizona Department of Health Services said. The department recommended emptying, scrubbing, covering or tossing anything holding water around your home after a monsoon.
If you think you might have been infected with West Nile virus, the CDC recommended to talk to your healthcare provider.
