California health officials urged residents to take precautions, including avoiding mosquito-infested areas, eliminating standing water that attracts the insects, using mosquito repellent, maintaining clean swimming pools and paying careful attention to window screens. The repellents should be applied routinely before going outside, since the virus is transmitted through the bite of an infected mosquito.  

They detected West Nile Virus in mosquitoes collected near Antioch’s Contra Loma Reservoir. The virus was detected in dead birds in 20 counties, including Los Angeles, Orange, Riverside and San Diego.

Officials warned that although this virus rarely causes death, it is extremely important for elderly people to pay more attention, as they are more prone to severe complications, as their immune system is weakened. Those with chronic medical affections and children are also advised to be more attentive.

The virus can be contacted by humans via mosquito bites that caught the disease from infected birds. The symptoms, similar with those of a flue, include nausea, fever, headaches, backache, lack of appetite, muscle aches. The West Nile virus can seldom lead to meningitis or death.

About 20 percent of people who are exposed to West Nile Virus end up with West Nile virus fever. A blood test can detect the presence of the virus.

The CDC estimated that in 2007 there were approximately 175,000 West Nile virus infections. The most numerous cases were reported in 2003 when the virus made 264 victims out of 9,862 registered cases.