West Nile virus cases highest for this time of year in more than 20 years; Maricopa County, Arizona reports the most
Last week. the Centers for Disease Control and Prevention (CDC) said in a statement that the West Nile virus (WNV) season in the United States is having its earliest start in 22 years.
At least 48 cases have been reported as of June 30, 2026: 38 have been cases of severe neuroinvasive disease. Since 2004, an average of 10 human disease cases has been reported to CDC by the end of June.
This surge is driven by early circulation of the virus, with 23 states reporting West Nile virus activity – also the highest number recorded over the last 10 years.
12 states have reported human cases already this year.
Arizona leads the country by a wide margin with 32 cases through June 30. Within Arizona, Maricopa County accounts for 29 of the cases, including 5 fatalities.
West Nile virus in the US: 20 years ago in NYC
Behind Arizona is Texas, reporting four human WNV cases to date.
West Nile virus is typically spread through the bite of an infected mosquito. Most people infected don’t show symptoms, but about 1 in 5 may develop a flu-like illness with fever, headache, and body aches. In rare cases—about 1 in 150—the virus can cause severe complications like encephalitis or meningitis, which might lead to paralysis, long-term disability, or death. Older adults, people with underlying health conditions, and those with weakened immune systems are at higher risk for severe illness.