West Nile Virus Activity Climbs in 2026, Primarily Impacting Arizona

The CDC reported a total of 48 human cases of West Nile virus in 2026, and a total of approximately 2000 people in the US are diagnosed with the virus each year. Of the cases, 38 have been considered neuroinvasive.¹

The CDC's ArboNET system—the national arboviral surveillance platform run jointly by CDC and state health departments—lists its 2026 case data for West Nile virus as current through June 30, 2026, with updates expected every 1 to 2 weeks.¹ The CDC notes several standing limitations on how these numbers should be read, such as mild, nonneuroinvasive illness being especially prone to underreporting since many infected people never seek care, so nonneuroinvasive counts should not be used to compare disease activity across locations or over time. Cases are also reported by county of residence rather than county of exposure, and there is an inherent lag between when a case is reported locally and when it is reflected in the CDC’s national figures.¹

For broader context, the CDC's baseline description of the disease notes that in a typical year, about 2000 people nationally are diagnosed with West Nile virus, more than 1300 develop severe illness affecting the central nervous system, and more than 130 die—figures the CDC also flags as underestimates, since most infections cause no symptoms or are attributed to another cause.²

Local Surveillance Shows a Faster Pace Than Last Year

County-level data illustrate how the season is unfolding in specific regions of the US. In Maricopa County, Arizona—historically one of the hardest-hit jurisdictions in the country—health officials reported 29 confirmed and probable locally acquired West Nile virus cases and 5 deaths as of July 1, 2026, versus 24 cases and 2 deaths reported on the same date in 2025.³

The county's 2025 season ultimately totaled 56 cases, and an additional 8 suspected 2026 cases remain under review and are not yet reflected in the confirmed count. Maricopa County's dashboard is updated weekly on Fridays, though it noted that data would not be refreshed the week of July 6, 2026, and it cautions that all current-year figures are provisional and that county-level tallies can differ slightly from state-reported numbers because of differences in reporting timelines.³

The CDC reported that 32 cases alone are in Arizona. Four cases were reported in Texas, 2 in both Colorado and Tennessee, and 1 across California, Oklahoma, Nebraska, South Dakota, Arkansas, Florida, and Pennsylvania.¹

No Vaccine, No Antiviral: What This Means for Pharmacists

West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States, and no licensed vaccine or medicine exists to prevent or treat it in people. CDC's clinical guidance for health care providers describes management as entirely supportive. Patients with mild illness are directed toward OTC medication for fever, pain, and headache, along with hydration and rest. Those with severe meningeal symptoms need pain control and antiemetic therapy, and patients with encephalitis require close monitoring for elevated intracranial pressure, seizures, or airway compromise. Further, patients with acute flaccid myelitis need close monitoring for rapidly developing neuromuscular respiratory failure that can require prolonged ventilatory support.⁴

That treatment gap puts weight on prevention counseling, an area where pharmacists are well positioned to help. The CDC recommends that patients use an Environmental Protection Agency–registered insect repellent, wear long, loose-fitting shirts and pants, avoid outdoor exposure between dusk and dawn, and use window and door screens or air conditioning to keep mosquitoes out of the home.⁴

“Regarding West Nile virus, avoiding mosquito bites is the best prevention method that health care practitioners should be counseling on,” Gretchen Garofoli, PharmD, BCACP, clinical professor in the college of pharmacy at West Virginia University, said. “There are not currently any medications or licensed vaccines to prevent West Nile virus, so utilizing methods to prevent mosquito bites such as using an insect repellent and wearing long, loose-fitting clothes are important when spending time outdoors.”

Garofolia added that pharmacists can also help patients choose insect repellent for them and their families.

The CDC also notes that people who are immunocompromised because of underlying conditions or taking immunosuppressive or immunomodulatory medications face a higher risk of severe illness and death from West Nile virus and other mosquito- and tick-borne infections, making risk counseling especially relevant for patients managing chronic conditions through the pharmacy.⁴

The CDC also flags transmission through blood transfusion and organ transplantation. Blood and some organ donors in the United States are screened for infection, and people with confirmed West Nile virus infection are asked not to donate blood for 120 days after their illness, Garofoli added. Health care professionals are encouraged to report any suspected transfusion- or transplantation-associated case promptly to the state or local health department.⁴

“If a patient has a fever due to West Nile virus, pharmacists can counsel them on the OTC fever-reducing treatment options and dosing recommendations based on patient-specific factors,” she said. “Pharmacists should also counsel patients on when to seek additional medical attention if symptoms worsen.”

A Disease That Has Changed Character Since Its US Arrival

West Nile virus was unknown in the Western Hemisphere until an outbreak of severe encephalitis emerged in New York City in the summer of 1999—the first identification of this Old World flavivirus outside Africa, the Middle East, and Asia. Historically, the virus had caused sporadic, generally mild febrile outbreaks dating back to its original 1937 isolation in Uganda, with only occasional reports of neuroinvasive disease, such as during a 1957 outbreak among elderly nursing home residents in Israel.^5,6

Beginning around 1996, outbreaks in Romania, Morocco, Tunisia, Italy, and Israel showed a shift toward more frequent epidemics with higher rates of central nervous system involvement and fatality, particularly among older adults—a pattern that carried over when the virus reached New York.^5,6

Within 3 years of its 1999 detection, the virus had spread from a 6-county area around New York City to 44 states, the District of Columbia, and 5 Canadian provinces, culminating in the largest outbreak of West Nile meningoencephalitis ever recorded during the 2002 season.⁵

The virus reached its largest single-year case count in 2003, at 9862 reported human cases nationally, after encountering an additional, highly efficient mosquito vector, Culex tarsalis, across the irrigated farmlands of the Midwest and the Rocky Mountain front range. Since 1999, West Nile virus has caused more than 37,000 reported human cases in the United States and is considered a permanent, if cyclical, feature of the country's arboviral landscape.⁶

“Pharmacists play an important role in educating our patients about infectious diseases and prevention methods,” Garofoli said. “In some instances, pharmacists can assist with or perform testing for certain infectious diseases and can sometimes even prescribe treatments depending on their state’s Pharmacy Practice Act.”

REFERENCES

1. Centers for Disease Control and Prevention. Current Year Data (2026). West Nile Virus. June 30, 2026. Accessed July 6, 2026. https://www.cdc.gov/west-nile-virus/data-maps/current-year-data.html

2. Centers for Disease Control and Prevention. About West Nile. West Nile Virus. September 10, 2025. Accessed July 6, 2026. https://www.cdc.gov/west-nile-virus/about/index.html

3. Maricopa County Department of Public Health. Vector-Borne & Zoonotic Reports. Maricopa County, AZ. July 1, 2026. Accessed July 6, 2026. https://www.maricopa.gov/4236/Vector-borne-Zoonotic-Reports

4. Centers for Disease Control and Prevention. Clinical Treatment and Prevention. West Nile Virus. August 19, 2025. Accessed July 6, 2026. https://www.cdc.gov/west-nile-virus/hcp/treatment-prevention/index.html

5. Sejvar JJ. West Nile virus: an historical overview. Ochsner J. 2003;5(3):6-10.

6. Roehrig JT. West Nile virus in the United States—a historical perspective. Viruses. 2013;5(12):3088-3108. doi:10.3390/v5123088