Last month, two women in Stanislaus County became the first confirmed human cases of West Nile virus in California this year. Their infection was discovered only after the two women donated blood.
In a statement, California Department of Public Health Director Dr. Mark Horton said, "The most important step people can take to prevent West Nile virus infection is to protect themselves from being bitten by a mosquito."
The virus is most commonly transmitted to humans and animals through a bite from an infected mosquito.