U.S. reports highest West Nile virus cases by late June since 2004

The U.S. has recorded 48 West Nile virus cases through the end of June, the highest number reported by this date since 2004, officials said. Thirty-eight of those cases were classified as severe neuroinvasive disease. The Centers for Disease Control and Prevention said the total exceeds the typical average of 10 cases by the end of June.

Twenty-three states have reported virus activity, also the highest number in the past decade.

Case distribution and risk groups Arizona accounts for 32 of the 48 cases.

West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States and causes roughly 130 deaths annually. Infections can produce brain swelling and long-term disability or death, though these outcomes occur in fewer than 1 percent of cases. Seniors and people with underlying medical conditions face higher risk.

Transmission and prevention Most infected people show no symptoms, while one in five develop fever, headache, body aches, joint pain, vomiting, diarrhea, or rash. No specific treatments exist for the virus. The virus spreads through bites of infected mosquitoes.

Peak transmission occurs from June through October, with diagnoses typically highest in late August and early September. Health officials recommend using Environmental Protection Agency-registered insect repellent, installing window and door screens, wearing long clothing, and avoiding outdoor activity between dusk and dawn.