Prosper and Celina residents are in the middle of peak mosquito season, and Denton County's West Nile virus threat keeps growing.

Denton County Public Health (DCPH) confirmed Tuesday, Sept. 8, that a fourth person in the county has tested positive for West Nile virus this year. The patient lives in the city of Denton and was diagnosed with West Nile Virus Neuroinvasive Disease, the most serious form of the illness. DCPH declined to release further personal details, citing patient confidentiality.

No vaccine exists.

Juan Rodriguez, DCPH's assistant director and chief epidemiologist, said the latest case is a reminder that mosquito-borne illness remains a threat across the county. He urged residents to take steps to protect themselves and their families from mosquito bites.

Each of the four 2026 patients was diagnosed with the neuroinvasive form, according to the county's individual case announcements. The first case was confirmed in a Flower Mound resident, according to Flomobee. A second patient, living in The Colony, was reported July 30. A third, in the northwest quadrant of unincorporated Denton County, was announced Aug. 28.

Neuroinvasive disease can cause encephalitis or meningitis and requires hospitalization. No medicine prevents West Nile virus in people, according to DCPH.

Prevention steps as mosquito season peaks

DCPH conducted multiple rounds of truck-based ground fogging this summer after mosquito traps tested positive for West Nile. Fogging zones in July and August included areas south of Hackberry and west of Frisco, and north of Highway 380 east of Teel Parkway near Artesia. No new fogging has been announced in connection with the fourth case.

The agency urges residents to follow its "Drain, Dress, Defend" guidance:

  • Drain standing water in yards and neighborhoods. Empty bird baths, flowerpots and clogged rain gutters. Use BTI briquettes (mosquito dunks) in water that cannot be removed.
  • Dress in long sleeves and pants outdoors. Spray repellent on thin clothing.
  • Defend with EPA-registered repellent containing DEET, Picaridin or Oil of Lemon Eucalyptus.

When he announced the third case on Aug. 28, Rodriguez warned that mosquito traps across the county continued to test positive. "As kids return to sports activities and community members spend time outdoors, it is important to take precautions to prevent mosquito bites," he said at the time.

Residents can track mosquito activity and fogging schedules at DentonCounty.gov/WNV or call DCPH at (940) 349-2900.