Visalia, Fresno repel their chances of contracting West Nile Virus

After two indications of the West Nile virus this year, Central Valley mosquito control districts are warning residents and telling them how they can prevent infection

(Center for Disease Control)
(Center for Disease Control)
Karis Caddell
Published June 20, 2023  • 
2:00 pm

VISALIA – California’s increased rain has flooded the Valley with a new generation of mosquitos, some of which have West Nile virus. Delta Mosquito and Vector Control District – as well as the Fresno Mosquito & Vector Control District – have warned residents to exterminate their chances of infection by taking precautions.

After storms swept through California this year, stagnant water became a concern for Visalia’s vector control district as West Nile virus infected mosquitoes staked their claim in the Central Valley. The Delta Mosquito and Vector Control District reported mosquito samples tested positive for West Nile virus and is now encouraging residents to minimize their risk of infection. 

“We’re here for [residents] to protect them from mosquito bites and also for mosquito-borne diseases and to work with them. Together we can definitely reduce the problem,” Dr. Mustapha Debboun from the Delta Mosquito & Vector Control District told the Sun-Gazette in April. “It’s a team effort.”

This is the district’s second indication of West Nile virus this year and the first dead bird positive with WNV. Three mosquito samples were collected between East Street Johns Parkway and East Goshen Avenue in east Visalia. The dead bird was collected near West Ferguson Ave and North Sallee Street 

West Nile virus is transmitted to people and animals through the bite of an infected female mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes then spread West Nile virus to people and other animals by biting them. 

Unraked leaves, planters, toys, littering of water bottles and cans all carry stagnant water, according to Debboun. In order to keep residents safe from mosquitoes during such a wet year, Debboun said that people are going to have to work alongside the vector control district to make that a reality.

Mosquitoes lay eggs in stagnant water frequently, and not just one egg at a time, Debboun said that a female mosquito can lay roughly 500 eggs at once. Residents may see mosquitoes gravitate to their homes if there is a lot of standing water or litter. The influx of water scattered throughout the area could possibly result in an increase in the mosquito population; however, the vector control district will be measuring that throughout the mosquito season.

Fresno Mosquito & Vector Control District manager, Ryan McNeil explained how the increased rainfall is affecting the Central Valley.

“With all of the rainfall this year mosquito districts were the only ones really in the Valley that benefit from a drought,” McNeil said. ”We do have a greater abundance of mosquitoes but we actually have less disease – mosquito disease – when there is more water.”

McNeil explained that less water in the Valley requires all animals and insects to congregate at the same water source in the area. When all the animals are sharing the same water they are also sharing and spreading diseases as well. The increased number of water sources keeps animals from congregating and spreading illness.

According to McNiel, there have been no positive cases of the West Nile virus in Fresno County so far but that doesn’t mean residents are out of the woods. He explained that Fresno County typically doesn’t have positive cases until early July and that could be the case this year.

McNiel emphasized the importance of preventing the accumulation of standing water around properties and houses as well as inspecting homes for leaking hoses and pipes to lessen mosquitos and the spread of disease. 

While most people infected with West Nile virus will have no symptoms, others will develop fever, headaches and body aches. Some cases require hospitalization and, in rare cases, death occurs. People with symptoms should contact their healthcare provider. Adults over 50 years old and people with compromised immune systems are at increased risk of serious complications. However, anyone who develops symptoms should seek medical care immediately.

Reduce the risk of contracting mosquito-borne diseases such as West Nile virus by following these guidelines: 

  • Prevent mosquito bites by using an EPA-registered insect repellent when going outside around dawn and dusk, when these mosquitoes are most active. Follow the instructions listed on the EPA-registered insect repellent product label.
  • Cover up. Wear long sleeve shirts and long pants when mosquitoes are most active to reduce bites.
  • Check window and door screens to prevent mosquitoes from entering your home.
  • Reporting and testing dead birds is one way to check for the presence of West Nile virus in the environment. 

Prevent mosquitoes around your home:

  • Inspect yards for standing water sources. Drain water that collects under potted plants, bird baths, tires, and any other water-holding containers.
  • Screen the openings of lawn drains.
  • Clean and scrub pet dishes and water features weekly.
  • Swimming pools, ponds, and fountains require working pumps and regular maintenance. Report neglected swimming pools anonymously to Delta Mosquito and Vector Control District for treatment.
  • Request free mosquitofish for backyard ponds, horse troughs, or neglected swimming pools. Free mosquitofish are available at the District office located in Visalia at 1737 W Houston Ave.


Every effort is being made to locate areas of standing water where mosquitoes may breed, including but not limited to catch basins, storm drain systems, and neglected swimming pools. Neglected swimming pools continue to be a mosquito breeding issue in the District. Neglected swimming pools can be reported to the District anonymously for treatment at 559-732-8606. 

Horses are very susceptible to West Nile virus and can be vaccinated. Horse owners are advised to contact their veterinarians regarding timely vaccinations. 

For information about the Delta Mosquito and Vector Control District, West Nile virus or to request District services, visit or call 559-732-8606.

For more information about Fresno Mosquito and Vector Control District, residents can visit To report dead birds to the California dead bird hotline call 1-877-WNV-BIRD.

Karis Caddell