West Nile Virus Detected in Mosquitoes in Orange County, California

Public health officials have announced that mosquito samples collected from Anaheim and Garden Grove in Orange County have tested positive for West Nile virus, marking the first confirmed virus activity in the area this year. On July 22, these findings were disclosed, highlighting the presence of four positive mosquito samples in these cities, although no human cases have been reported so far.

A dead bird found in Garden Grove also tested positive for West Nile virus, reinforcing concerns about the ongoing circulation of the virus within the community. According to Amber Semrow, Director of Scientific and Technical Services at the Orange County Mosquito and Vector Control District, the detection of virus in both mosquitoes and a bird indicates active transmission, especially during the warm summer months when conditions favor mosquito proliferation.

Overview of West Nile Virus:

• The virus is the leading cause of mosquito-borne disease in the continental United States.
• It is primarily transmitted to humans through bites from infected mosquitoes.
• Mosquito season runs from summer through fall.
• In California, there have been three human cases reported in 2025, including one fatality.
• Last year, there was one human infection and 53 positive mosquito samples in Orange County.

Preventive Measures:
Residents are urged to eliminate standing water around their properties to prevent mosquito breeding. Additional precautions include keeping windows closed or screened, wearing long-sleeved clothing and insect repellent, and avoiding outdoor activities during peak mosquito activity at dawn and dusk.

Health Impact:
Most people infected with West Nile virus remain asymptomatic. Approximately 20% develop fever and flu-like symptoms, while around 1 in 150 may experience severe illness, which can be life-threatening.

Source: https://medicalxpress.com/news/2025-07-west-nile-virus-mosquito-samples.html