West Nile Virus First Human Cases Reported in Texas and California Counties

Tarrant County, Texas, announced its first confirmed human West Nile virus case of 2026 on July 24. The patient is suffering from the neuroinvasive form, which affects the brain, spinal cord or surrounding membranes. Tarrant County Public Health did not disclose the patient’s age or condition but noted that 86 mosquito pools in the area have tested positive this season, indicating widespread viral activity.

Fresno County, California, also reported its first human West Nile case of 2026 on July 24, but the infection was identified through routine screening of a blood donor rather than through clinical symptoms. The Fresno County Department of Public Health emphasized that most infections are asymptomatic and that blood‑donor testing serves as an important surveillance tool, capturing cases that would otherwise go unnoticed. Similar first‑case announcements were made by Kings County on the same day.

Both counties highlighted that roughly 80% of West Nile infections are asymptomatic, about 20% develop mild fever, and less than 1% progress to the severe neuroinvasive disease seen in Tarrant County. Ongoing mosquito surveillance and blood‑donor screening remain key to monitoring the virus’s spread this season.