SALINAS, Calif. -- The West Nile virus is striking California earlier than usual this year.

State health officials said they have detected West Nile in mosquito pools and horses in eight California counties, including Santa Clara.

They said higher-than-normal spring temperatures are to blame.

So far, there are no human cases. But Salinas Valley Vector Control has begun spraying earlier than usual.

Health officials said back yards are a big concern and that any standing water is a haven for mosquito larvae.

Mosquitoes get West Nile from birds.

More than 150 dead birds have been found in Monterey County, but officials said none were infected with West Nile.