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West Nile update: Heat and drought could spread the virus

A stock photo shows mosquito larvae in a puddle of water on June 29, 2012 in Pleasant Hill, California. Officials recommend calling your county's vector control district for help with cleaning up standing water.
A stock photo shows mosquito larvae in a puddle of water on June 29, 2012 in Pleasant Hill, California. Officials recommend calling your county's vector control district for help with cleaning up standing water.
Justin Sullivan/Getty Images

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The California Public Health Department announced West Nile Virus activity has gone up across the state. But in Southern California, it’s a slightly different story.

Officials in the counties of Los Angeles, Orange and San Bernardino said West Nile activity is either normal or lower than average for July in their districts.

No human infections have been reported in California this year. The main indicators of West Nile Virus activity are positive testing in mosquitos and dead birds.

In Orange County, only 2 percent of mosquitos have tested positive for the virus, said Jared Dever with Orange County Vector Control. At the same time last year, 20 percent of mosquitos were infected. The numbers for birds are even starker, dropping from 26 percent to 2 percent, he said.

“What happened last year is a lot of birds got bit by infected mosquitos,” Dever said. “Those birds that didn’t die last year are innoculated. They are now immune to the virus.”

He described the cycle of infection and immunity in birds and mosquitos as a “dance.” These highs and lows are by no means unusual to vector control specialists.

Across the state, infected mosquitos are up while infected dead birds are down, according to the interagency California West Nile Virus Website.

Officials agree that it’s too early to tell whether 2015 will compare to last year, nearly the worst on record for West Nile Virus in California.

Kelly Middleton of Los Angeles County Vector Control said summer heat and droughts tend to help the virus spread. The drought means less water is flowing through urban Los Angeles’ drains, making fertile breeding conditions for mosquitos.

“The underground areas tend to clog up with a lot of leaf litter and trash, and it doesn’t get flushed out by the big storms,” Middleton said. “So we tend to have more problems in these drought years, especially in our undergrounds.”

At this time last year, 5 people had been reported infected. It was one of the worst years on record, with more than 800 human cases reported, 31 of them fatal.

Humans contract the virus from mosquitos. The CDC says the vast majority of people infected with West Nile show no symptoms, while less than 1 percent develop sometimes fatal neurological problems.

How to avoid West Nile Virus

Raymond Britain, project manager at San Bernardino County's Environmental Health Services, said his county has not seen unusually high West Nile Virus numbers. He recommended some simple steps for avoiding the illness. "It starts with people being proactive," he said, and it comes down to avoiding exposure to mosquitos.

Britain said, so far, San Bernardino officials have found West Nile Virus in Rialto and Fontana.