When UC Davis confirmed on Sept. 15 that a dead crow in Los Angeles County carried West Nile virus, it was the first evidence of West Nile activity in birds in California. Now UC Davis has confirmed six more infected crows in Los Angeles County and an infected sparrow in Riverside County.

UC Davis, which has the largest West Nile testing and research program in California, also collected and identified the first West-Nile-carrying mosquito in California. That mosquito was trapped in early August in Imperial County, near the Salton Sea.

As of today, in the continental United States, only three states have not recorded West Nile infections in any animal -- Oregon, Washington and Idaho. Those three, plus California, West Virginia and Maine, are the only states with no locally acquired human infections.

The arrival of somewhat cooler weather does not mean that West Nile risk has declined, said John Edman, director of the UC Davis Center for Vectorborne Disease. Mosquitoes in California bite well into the fall, and even during the winter months in Southern California, Edman said.

Until public health authorities advise otherwise, people should continue to wear long sleeves, long pants and mosquito repellent if they are outdoors between dusk and dawn. Year-round, they should try to eliminate mosquito breeding sites around their homes by emptying standing water and cleaning out rain gutters.