A small number of wild birds have tested positive for West Nile virus in Redwood City, Menlo Park and other parts of San Mateo County, prompting authorities to ask the public to report any dead birds they encounter.

So far, eight birds are confirmed to have died from the disease. Birds that have tested positive have been found in Burlingame (1), Redwood City (2 in the Redwood Shores area), San Carlos (1), and Menlo Park (4). Additional mosquito trapping and testing done in areas where dead birds were located has not found any positive mosquitoes, the San Mateo County Mosquito and Vector Control District said.

The virus is spread to humans through infected mosquitoes that pick up the disease from wild birds, the primary source. The district said that some birds infected with the virus don't become ill, but others die.

In people, West Nile virus might not cause symptoms, but it can cause severe illness. People might experience months of recovery, neurological symptoms such as encephalitis, meningitis and death, according to the U.S. Centers for Disease Control and Prevention (CDC).

Dead birds are often the first sign of active West Nile virus in an area. Some signs of West Nile virus in birds include uncoordinated movement, a lack of energy, and difficulty breathing. According to the district, crows, jays, ravens and magpies are the most likely to get sick and die from the virus.

About 1 in 5 people who are infected with the virus develop a fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Fatigue and weakness can last for weeks or months, according to the CDC.

Approximately 1 in 150 infected people develop a severe illness affecting the central nervous system, such as brain inflammation or inflammation of membranes surrounding the brain and spinal cord, which can take months of recovery. People older than 60 and those with medical conditions such as cancer, diabetes, hypertension, kidney disease, and organ transplant recipients are most at risk for severe illness. About 1 in 10 people die.

Authorities have received reports of 233 dead birds in San Mateo County as of Sept. 22, and 55 were considered suitable for testing. The mosquito abatement district has also tested thousands of mosquitoes, but so far, all have tested negative for the virus, according to the county vector control district.

The virus has been detected in most counties statewide, and 24 counties had human cases. Statewide, there were 124 human cases; six were fatal. The dead bird hotline received reports of 5,203 dead birds in California so far this year; 1,641 have been tested, and 654, or 40%, tested positive for West Nile virus. In addition, 3,983 mosquito samples, 155 sentinel chickens and 21 horses have tested positive for the virus, according to the county vector control district.

The district is asking the public to report dead birds through the California West Nile Virus and Dead Bird Call Center online at westnile.ca.gov/ or call 877-WNV-BIRD. The state will notify the county, and a district employee will collect the bird for testing. More information can be found here.

The Santa Clara County Vector Control District used a spray treatment to target affected areas on Thursday, Sept. 14.