A dead American crow discovered in central Danville on Tuesday tested positive for West Nile virus, becoming the fourth bird in the town found to be infected with the virus this year, according to the Contra Costa Mosquito and Vector Control District.
Since July, five dead birds found in the San Ramon Valley have reportedly tested positive for the virus, which can be transmitted from birds to humans via mosquitoes. Almost half of the dead birds to test positive in the county have been discovered in San Ramon and Danville.
"Mosquitoes are enjoying their last hurrah before they hibernate for the season and are aggressively seeking a blood meal," said district program supervisor Sheila Currier.
"Our surveillance tells us that the source of the mosquitoes is not where we are fogging, but it's where the mosquitoes are going. These mosquitoes can travel up to five miles from their source and have come to rest in areas that are consistently moist and lush. Everyone should wear mosquito repellent when outdoors, no matter where you are in the county," she added.
Officials found the virus-positive dead crow at Everett and Paraiso drives, between John Baldwin Elementary School and Osage Park, on Tuesday. That discovery came eight days after a dead American crow was located at Silver Lake and El Capitan drives -- it was also infected with West Nile virus.
The other West Nile virus activity in the San Ramon Valley occurred in dead birds found Sept. 27 at Podva Road and San Ramon Valley Boulevard, Sept. 9 at Dos Rios and Bollinger Canyon roads in San Ramon and July 23 at Roan and Clydesdale drives in Danville, according to the district.
Countywide, there have been 11 birds, seven groups of mosquitoes, 16 chickens and one Brentwood horse reported as virus-positive this year. No human cases have been reported in Contra Costa County to date.
Most cases of the virus in humans are mild and include symptoms such as fever, headache, tiredness, body aches and swollen lymph glands, according to district officials. Severe cases of West Nile virus can be fatal.
The most recent Contra Costa County human fatalities from the virus occurred in 2006, when two people died, officials said.
Birds are the reservoir for West Nile virus, which can be transmitted to humans via mosquitoes.
The two species of mosquitoes in the county capable of transmitting the virus prefer to feed on birds, but people can become infected when a mosquito bites an infected bird and then a person, district officials said.
The district is planning to conduct preventative fogging for adult mosquitoes Thursday evening in the area of Delta View Golf Club in Pittsburg, near where a sampling of mosquitoes tested positive for the virus earlier this month.
District officials preach prevention, encouraging people to wear mosquito repellents, avoid going outside at dawn or dusk when mosquitoes are often present, dump or drain standing water where mosquitoes could lay their eggs, and report dead birds and neglected swimming pools.
According to the district, most West Nile virus cases are not diagnosed and are "grossly under-reported."
For more information, call the district at 771-6195 or visit its website.