The proportion of mosquitoes infected by the West Nile virus in California has risen to its highest level ever, according to public health officials.
The virus has been detected in 36 counties year-to-date, and more than 181 human cases have been reported to the California Department of Public Health so far in 2014, according to a statement released Wednesday.
Only 101 human cases had been reported by the same time last year, and the five-year average is just 56, according to the latest numbers from WestNile.ca.gov, which is hosted by the public health department and other health agencies.
"Last week, 52 new human cases were reported to CDPH. We expect to see more people become infected as this is the time of year when the risk of infection is the highest," said Dr. Ron Chapman, director of CDPH, in the statement.
By far most of the human cases (61) have been reported in Orange County. Los Angeles, Fresno and Stanislaus counties have seen 24, 23 and 21 cases, respectively, according to the data.
Humans pick up the virus by being bitten by an infected mosquito, though for most people the risk is low. A very small number of people — roughly 1 percent — can develop serious neurologic illnesses such as encephalitis or meningitis, according to the statement.
The first deaths in L.A. and Orange counties were reported last week.