Last year was one of the most active for West Nile virus in California, said Dr. Karen Smith, state Department of Public Health director and state health officer.

Smith said in 2014, California had the second-highest number of human cases of West Nile virus (WNV) since the virus first showed up in 2003. The state recorded 801 West Nile cases, compared to 880 cases in 2005.

Orange County, with 263 cases, had the highest number in the state, while the highest incidence rate was in Glenn County, with 35.3 cases per 100,000 people, Smith said.

But 2014 was a record-breaking year for WNV activity in California, too, she said.

The number of fatal WNV cases, 31, exceeded all previous years, she said.

Among other records, the state reported 561 cases of West Nile neuroinvasive disease (WNND), the more serious neurological form of the disease that often results in encephalitis or meningitis.

The proportion of mosquitoes infected with WNV was the highest ever detected in California, Smith said, reaching epidemic conditions, while the prevalence of WNV infection in tested dead birds was 60 percent, the highest ever detected in California.

Smith said the ongoing severe drought may be contributing to the high amount of WNV activity, because sources of water for both birds and mosquitos are limited.

“As birds and mosquitoes sought water, they came into closer contact and amplified the virus, particularly in urban areas,” she said.

“The lack of water could have caused some sources of water to stagnate, making the water sources more attractive for mosquitoes to lay eggs.”

Smith said it isn’t possible to predict levels of WNV activity for this year because multiple factors are involved — such as climate, the numbers and types of birds and mosquitoes that are in an area and the birds’ immunity level.

But as weather warms, more mosquitoes will be in the area, she said.

“Unseasonably warm weather this year could lead to increased mosquito abundance and promote an early start to the WNV disease season,” she cautioned.

“The WNV season typically begins in the summer and tapers off in the fall months, with the highest risk for disease occurring in mid-July through September.”

She said WNV is transmitted to humans and animals by the bite of an infected mosquito.

“For most people, the risk of serious illness is low,” she said. But in fewer than 1 percent of those bitten, serious neurologic illness, such as encephalitis or meningitis, can develop.

Particularly vulnerable are those 50 and older and those with diabetes, high blood pressure or both.

Smith said her department recommends people reduce exposure to mosquito bites and West Nile virus by practicing what she calls “The Three Ds” — DEET, Dawn and Dusk, and Drain.

“DEET” is a reminder to apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus or IR3535 according to label instructions.

“Repellents keep the mosquitoes from biting you. DEET can be used safely on infants and children 2 months of age and older,” she said.

“Dawn and Dusk” are when mosquitoes are more likely to bite, so that reminder urges people to wear protective clothing and repellant if they are outdoors during those times.

“Make sure that your doors and windows have tight-fitting screens to keep out mosquitoes,” Smith said, and she added that screens with tears or holes should be repaired or replaced.

Finally, standing water should be drained, she said.

“Eliminate all sources of standing water on your property, including in flower pots, old car tires and buckets,” Smith said.

“If you know of a swimming pool that is not being properly maintained, please contact your local mosquito and vector control agency.”

She said all dead birds should be reported through the state’s West Nile website, www.westnile.ca.gov, or by calling 877-WNV-BIRD (968-2473).