California health officials warned Thursday that West Nile virus activity has reached a five-year high statewide, weeks after Los Angeles County reported its first human case of the year.
As of Aug. 14, 30 human cases of West Nile virus, including three deaths, had been reported in 13 California counties this year, according to the California Department of Public Health. The number of human cases is above the five-year average for this point in the year.
Los Angeles County health officials announced July 13 that an Antelope Valley resident was the county’s first confirmed human case of the virus this year. The resident was hospitalized after developing West Nile virus encephalitis following the onset of symptoms in late June.
“West Nile virus can be fatal, particularly for the elderly and immunocompromised,” CDPH Director and State Health Officer Dr. Erica Pan said in a statement. “August and September are peak periods of West Nile virus transmission in the state, so we urge everyone to take precautions to protect themselves against mosquito bites.”
Signs of West Nile virus activity have been detected in 32 California counties through surveillance of mosquitoes, dead birds, sentinel chickens and horses, according to CDPH.
More than 24% of dead birds identified through surveillance have tested positive for the virus, compared with a five-year average of 13%. Eight out of every 1,000 mosquitoes tested are positive, compared with a five-year average of five per 1,000, state officials said.
West Nile virus is transmitted to people and animals through the bite of an infected mosquito. While most people face a low risk of serious illness, the virus can cause potentially fatal neurological illnesses, including encephalitis and meningitis.
People 60 and older and those with diabetes, hypertension or chronic kidney disease are at higher risk of becoming seriously ill, as are people taking medications that suppress the immune system, according to CDPH.
State officials urged residents to use EPA-registered insect repellents containing ingredients such as DEET or picaridin, wear long sleeves and pants during times when mosquitoes are most active and make sure doors and windows have properly fitted screens.
Residents were also advised to eliminate standing water in flowerpots, buckets, old tires and other containers where mosquitoes can lay eggs.
Los Angeles County health officials have said the county averages 41 human West Nile virus cases annually over the last five years, excluding cases reported separately by the Pasadena and Long Beach health departments.
There is no vaccine or specific treatment for West Nile virus.