Mosquitoes collected from Chumash Park in Pismo Beach on July 9 and 10 tested positive for West Nile Virus, San Luis Obispo County officials announced July 26.
The Mosquito and Vector Management District of Santa Barbara County conducted the testing as part of a services contract with the city. The district treated Pismo Creek on July 18 with a biological insecticide that targets mosquito larvae. Several other wetland areas in and around the city—including Pismo State Beach—also received treatment.
The insecticide’s bacterial agent, Bacillus thuringiensis israelensis, paralyzes the digestive system of hatched mosquito larvae, preventing them from growing into adults. District General Manager Larry Fausett said the bacteria could impact other insects in the food chain, but not sufficiently enough to harm the local ecosystem.
“All in all, there is a negligible effect on the other fauna in the system where we are treating for mosquitoes,” Fausett said.
Not all patients who contract West Nile exhibit symptoms, but the disease can trigger a strong reaction in some cases. California public health agencies have reported four confirmed cases of West Nile in humans this year.
SLO County Health Officer Penny Borenstein advised the public to routinely dump sources of standing freshwater that might serve as mosquito breeding habitat.