Two dead birds tested positive for West Nile virus in Oakland and Pleasanton this week, the first confirmed cases of the year in Alameda County, officials said Wednesday.

The two birds, both American Crows, were reported by residents July 12 and July 16 in two separate ZIP codes, said Erika Castillo, environmental specialist for the Alameda County Mosquito Abatement District. One was found in Pleasanton just south of Interstate 580 in the Stoneridge mall area, the other in the Oakland hills on the east side of Interstate 580.

"We are intensifying all of our inspections and treatments in the areas where the birds were picked up," said Castillo. "West Nile virus is endemic to Alameda County, so we expect some activity every year."

A Culex quinquefasciatus mosquito is shown on a human finger. The Culex quinquefasciatus mosquito is a vector associated with transmission of the West Nile
A Culex quinquefasciatus mosquito is shown on a human finger. The Culex quinquefasciatus mosquito is a vector associated with transmission of the West Nile virus. (Centers for Disease Control and Prevention)

The discovery of the birds in Alameda County makes it the last Bay Area county to report cases of the virus in 2013, after a total 13 dead birds and two squirrels were found dead from the virus in Santa Clara, San Mateo and Contra Costa counties, according to the California Department of Public Health.

The only 2013 case in humans in the state of California occurred in a Sacramento man, who died in June after contracting the virus. Because of other underlying health conditions, it is not known if his death was a result of the West Nile infection.

2013 West Nile infections

The first reported case in Contra Costa County came in the form of a dead crow discovered June 26 near Yellowstone Drive and Hillcrest Avenue in Antioch, with four infected birds in Brentwood, Alamo and Concord following in the first two weeks of July, said Deborah Bass, public affairs manager for the Contra Costa Mosquito & Vector Control District. Four groups of infected mosquitoes were also trapped in Discovery Bay during those first couple of weeks.

Officials in Santa Clara County reported four infected birds, two in South San Jose July 1 and 2, and in Milpitas July 11 and 15, said Russ Parman, acting district manager of the Santa Clara County Vector Control District. Two infected squirrels were also discovered in South Sunnyvale July 5, the same day a group of infected mosquitoes were found trapped in the 3.75-square mile area surrounding Miner Park in South San Jose.

San Mateo County, while the first to report infected birds in San Mateo May 30 and June 2, has confirmed only two infected birds in Redwood City, an American Goldfinch June 12 and a red-shouldered hawk on June 17, said Brian Weber, operations director for the San Mateo County Mosquito and Vector Control District. The tests from the birds found in San Mateo came back negative from the state, and no infected mosquito populations have been identified within the county limits.

Personal protection

Since West Nile virus is a mosquito-transmitted disease, controlling the mosquito population is the top priority, said Castillo, noting that mosquitoes must have standing water to complete their life cycle. While West Nile activity could occur at any time of year, it peaks in the warmer summer months.

"The biggest thing is checking your yard and eliminating any standing water on property," Castillo said. She recommends residents put screens on their doors, wear long sleeves and pants when going outside and apply mosquito repellent containing either DEET, picaridin, IR3535, or oil of lemon eucalyptus. "Those are the most difficult sources for us to find and control, since we don't have access to everyone's yard."

According to Bass, reporting neglected swimming pools is extremely important because they can produce more than 1 million mosquitoes that can affect people up to five miles away. The Alameda County district routinely performs aerial surveys to monitor for neglected pools, Castillo said.

Between 2003 and 2012, there have been 3,625 statewide cases of West Nile virus in humans, 130 of which resulted in death. By the end of 2012, 479 cases had been reported, with 20 fatalities, according to the CDPH.

A person who has contracted the virus might first notice typical flu-like symptoms, such as fever, muscle aches and chills, Contra Costa district's lab director Steve Schutz said. If seeing a doctor for those symptoms, patients should tell their doctors if they've been bitten recently.

Residents are urged to report to the Department of Public Health any dead squirrels or wild birds, especially crows, ravens, jays, magpies and birds of prey that have been dead less than 48 hours. Reports can be made at www.westnile.ca.gov or by calling 877-WNV-BIRD, and additional information about the virus can be found at www.mosquitoes.org.

Staff writer Brittny Mejia contributed to this report. Contact Erin Ivie at eivie@bayareanewsgroup.com.