Mosquitoes collected this month in Pismo Beach have tested positive as carriers of West Nile virus.

The virus was isolated from mosquitoes collected on July 9 and 10 at Chumash Park, according to a recent news release by the San Luis Obispo County Public Health Department.

The mosquitoes were collected by staff from the Mosquito and Vector Management District of Santa Barbara County, with which the city of Pismo Beach has a contract.

Following the discovery, the district treated Pismo Creek and two freshwater ponds at Chumash Park on July 18 with an insecticide specific to mosquito larvae — it does not harm birds, fish, frogs, or other types of insects, according to the news release.

Mosquito breeding sources at Pismo Ecological Reserve, North Beach Campground, LeSage Riviera Golf Course and Oceano Campground were also treated.

The district will return in early August to do more trapping, inspection, and treatment for mosquitoes within the Pismo Beach city limits and at Pismo State Beach.

California has seen four confirmed human cases of West Nile Virus this year (one case each in Glenn and Sacramento Counties, and two cases in Los Angeles County), according to the release. Most people who are infected with the virus — which in rare cases can cause brain swelling — do not develop symptoms.

Warm weather creates advantageous breeding conditions for mosquitoes, and the public is encouraged to eliminate standing water in places where mosquitoes can breed, such as decorative ponds, bird baths or fountains; flower pots; pet bowls; animal troughs; clogged rain gutters; swimming pool covers; discarded tires; and buckets, barrels, cans or other small containers.

San Luis Obispo County's Public Health Services advises people to stay indoors between dusk and dawn, when mosquitoes are most active; apply insect repellent; wear long-sleeved clothes; and make sure doors and unscreened windows are closed.

As part of the state’s West Nile Virus surveillance effort, the California Department of Public Health has asked the public to report any dead birds that have been dead for less than 24 hour by calling 1-877-WNV-BIRD (1-877-968-2473).