Two more dead birds found in Danville tested positive for West Nile virus this month, but virus activity countywide should start slowing as cool autumn weather rolls in, according to the Contra Costa Mosquito and Vector Control District.
The American crows discovered on Oct. 3 near Old Farm Road and Contada Circle and on Oct. 4 near Green Valley and Blemer roads became the latest among six cases of virus-positive dead birds in the San Ramon Valley so far this year, district officials said.
The other San Ramon Valley cases occurred in Blackhawk on July 31, two in Alamo in early August and one in Danville on Aug. 23.
"It's common to get dead birds that test positive for the virus in the 680-corridor at this time of the year," said district scientific program manager Steve Schutz, Ph.D. "However, the risk of West Nile virus should decrease countywide as the overnight temperatures drop."
Schutz also advised that the current short-term weather forecasts show the need for mosquito awareness during the fall.
"But, rainwater now and warmer temperatures next week means we still have to be vigilant in our control of mosquitoes. It's really important to dump standing water after the rain," he said.
Overall, Contra Costa County has recorded 49 positive tests for West Nile virus this year, including one human case, according to local and state officials.
The other cases recorded to date were 10 mosquito samples (all in East County), five sentinel chickens (in Holland Tract and Oakley during the summer) and 33 dead birds, with the latest being American crows found in Walnut Creek and Concord on Tuesday.
The location and date of the lone Contra Costa County human case have not been reported.
There have been 310 human cases among 29 counties recorded statewide this year, according to the California Department of Public Health website.
Eleven people with West Nile virus have died in California so far in 2016, according to state officials. None occurred in Contra Costa County, and the nearest fatalities were in Sacramento and San Joaquin counties -- one each.
The most recent Contra Costa County human fatalities from the virus occurred in 2006, when two people died, officials said. In all, 56 people in the county have been diagnosed with West Nile virus since 2005.
In humans, most cases of the virus 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.
Birds are the reservoir for West Nile virus, which can be transmitted to humans via mosquitoes. So, local officials recommend immediately reporting sightings of dead birds or neglected swimming pools where mosquitoes could populate.
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 preaches prevention, encouraging people to wear mosquito repellents, avoid going outside at dawn or dusk when mosquitoes are often present and dump or drain standing water where mosquitoes could lay their eggs.
For more information, visit the district's website.