BAKERSFIELD -- The state health department is tracking a surprising cause for the early rise in human West Nile virus cases.

Officials say the lack of rainfall is causing more human West Nile cases, especially in Kern County, where 22 of 27 human cases statewide in 2007 have been diagnosed.

Kern County also has California's only West Nile-related death of the year. 96-year-old Marguerite Wilson died earlier this month from the disease.

Scientists typically cite pools of standing water left after rain storms as prime breeding ground for the mosquitoes that carry the disease.

But officials believe the drought foretold by this winter's thin Sierra snows could be crowding diseased birds into more scarce watering holes, where they're being bitten by mosquitoes that transfer the germs to humans.

The health department also says mortgage foreclosures leading to a lack of swimming pool maintenance is increasing the volume of mosquito larvae.