Mosquitoes that can carry West Nile test positive for St. Louis Encephalitis in Fresno

Mosquitoes trapped in Fresno have tested positive for St. Louis Encephalitis.

Fresno County health officials said Thursday the infected mosquitoes were in the areas of East Floradora Avenue and Highway 41, plus Shields and Van Ness avenues.

The Culex mosquitoes that carry St. Louis Encephalitis are also capable of infecting people with West Nile virus. There is no vaccine for humans who are infected with either virus.

Most people infected with West Nile and Saint Louis Encephalitis have no symptoms, however, the viruses can affect the central nervous system. One in five people may develop a fever along with other symptoms, and severe neurological effects can occur and may be permanent. The infections can be fatal..

St. Louis Encephalitis has been making a comeback in California since fading about 20 years ago. Fresno County found mosquitoes positive for St. Louis Encephalitis last year near Polk and Bullard avenues in northwest Fresno. In 2016, a batch of mosquitoes tested positive for the virus in an area outside of the city limits. One person became infected, was hospitalized and recovered.

"We do expect to find more mosquitoes that will test positive for St. Louis Encephalitis this year," said Ryan McNeil, manager at the Fresno Mosquito & Vector Control District.

Mosquitoes carrying West Nile virus continue to be prevalent in California. Last year, 553 people became infected in the state and there were 44 deaths. There were no West Nile virus deaths reported in the central San Joaquin Valley in 2017 but Fresno County had 14 infections, Kings County had five infections, Madera County had two, Merced had 11 infections and Tulare County reported 13 infections.

A different mosquito, the Aedes aegypti, that can spread yellow fever and Zika virus, is beginning to bite in Fresno, McNeil said. "It's a hardier mosquito that likes to breed in containers," he said. "Residents need to start thinking about the amount of standing water around their homes. This mosquito can breed in just a teaspoon of water that is laying around."

Zika poses a threat to pregnant women or women who want to become pregnant because it can cause birth defects like microcephaly, a brain disorder.

Reducing exposure to mosquito bites is the best way to prevent infection of Zika, West Nile virus and St. Louis Encephalitis, and officials at the Fresno County Department of Public Health advise people to take precautions, including using insect repellent when outdoors and stopping mosquitoes from breeding by emptying standing water from flower pots, buckets, barrels and tires.

For more information about mosquitoes and preventing bites, visit the Fresno Mosquito Vector Control District web site or call 559-268-6565. For more information about St. Louis Encephalitis visit the federal Centers for Disease Control and Prevention web site.

This story was originally published July 5, 2018 at 11:54 AM.