A bird found in Lake Tahoe along with five others and a horse have tested positive for West Nile virus, the El Dorado County Environmental Management Department has reported.
The horse, located in the Placerville area, is being treated for the illness. Confirmatory testing was conducted by the California Animal and Food Safety Laboratory, at University of California, Davis.
The birds were found in California in South Lake Tahoe, Cool, Somerset, Placerville, Shingle Springs and Camino.
Horses are highly susceptible to West Nile virus - approximately half of the horses that get the virus die or are euthanized. A vaccine is available for horses.
Clinical signs of the infection in horses include stumbling, staggering, wobbly gait, loss of coordination, weakness and paralysis. Humans and animals cannot get West Nile virus from an infected horse; it is only spread by the bite of an infected mosquito.
In El Dorado County, there have been a total of 17 birds and one horse that have tested positive for West Nile virus. There have been no human cases. In California, there have been eight West Nile virus-related fatalities and more than 300 people diagnosed with the disease this year.
"It is critical that people understand that there is an increased risk for disease at this time and they need to take precautions now to avoid mosquito bites," said Virginia Huber, spokeswoman for El Dorado County's West Nile Virus Task Force.