SAN MARCOS — State officials detected West Nile virus in two mosquito samples collected from different sites near San Marcos on July 8, 2026. The findings mark the first confirmed presence of the virus in Hays County during the 2026 season.

No human cases of West Nile virus have been reported in Hays County to date. State data shows five human cases have been reported elsewhere in Texas this year, all in the Houston area.

West Nile virus is a species of virus first identified in the United States during a 1999 outbreak in New York City. Since then, it has become endemic in many parts of the country, with seasonal activity typically peaking in summer months.

Most people do not experience symptoms after being bitten by a West Nile virus-infected mosquito. Approximately 20% of infected individuals may develop fever, headache, body aches, rash, or other flu-like symptoms. Less than 1% develop severe symptoms, which can include high fever, neck stiffness, disorientation, muscle weakness, and central nervous system infection.

Adults 50 years and older and people with weakened immune systems face an increased risk of severe illness from West Nile virus. Public health officials advise several preventive measures to reduce mosquito bite risk, including using Environmental Protection Agency-approved repellents and following label instructions.

Additional recommendations include wearing long, loose, and light-colored clothing when outdoors and draining or treating standing water to reduce mosquito breeding. San Marcos, located on the Interstate 35 corridor between Austin and San Antonio, has seen its population grow from 44,894 in 2010 to 67,553 in 2020, increasing the number of residents potentially affected by seasonal mosquito activity.

While Texas begins its local monitoring season, other states are also reporting significant activity. West Nile virus has been detected in 24 counties across California this year, where officials have recorded 261 positive mosquito samples and 133 positive dead birds statewide so far.

Why It Matters

The detection of West Nile virus in local mosquito populations signals the start of seasonal transmission risk in Hays County, prompting public health messaging even in the absence of human cases. Early mosquito surveillance allows officials to alert communities before infections potentially spread, especially to vulnerable populations such as older adults and those with compromised immunity.

With five human cases already confirmed in Texas and widespread activity in other states like California, the findings near San Marcos underscore the ongoing need for preventive measures during peak mosquito months.