Conditions created by ongoing drought in California could expose state residents to dangerous, sometimes fatal infectious diseases previously restricted to regions with hot, dry climates, health officials say.

The state saw a record-breaking number of deaths last year linked to West Nile Virus, with 31 fatal cases reported, the California Department of Public Health reported.

The increase may be down to the effects of the drought, as it shrinks rivers, lakes and streams and leaves behind stagnant water that is prime breeding ground for the mosquitoes that carry the virus, experts suggest.

More than 800 cases of the virus disease were recorded in 2014, the second-highest number ever reported in the state since the disease was first detected there in 2003, officials said.

As mosquito numbers increase, so do the numbers of birds found to be carrying the virus, they said.

"As birds and mosquitoes sought water, they came into closer contact and amplified the virus, particularly in urban areas," said Dr. Karen Smith, director of the California Department of Public Health. "The lack of water could have caused some sources of water to stagnate, making the water sources more attractive for mosquitoes to lay eggs."

West Nile Virus symptoms can include high fever, a stiff neck or severe headache, and sufferers often exhibit confusion.

It is most serious for those who are struck with a neurological form of the disease which can result in swelling of the brain, and which can be fatal. Of the more than 800 cases in California, 561 patients developed a serious neurological form of the disease.

For most healthy individuals the risk of a serious case is low, but people age 50 and above or those with high blood pressure or diabetes face increased risks of developing complications, officials said. They encouraged residents to drain stagnant water areas, wear protective sprays and clothing, especially at dawn and dusk when mosquitoes are most active, and use insect repellent sprays.

West Nile Virus isn't the only disease that could increase if the drought continues, they added; there is a concern cases of Valley Fever could also rise.

A fungus known as Coccidioides that grows in soil causes the disease, which brings on fever, cough and headaches and can in some cases be fatal.

As soil is dried out, the fungus can spread through the air in the form of released spores, and there is concern drier conditions with the ongoing drought would increase the rate of Valley Fever infections, says Art Reingold, an expert in infectious diseases who teaches at the University of California, Berkeley.

"It's so clearly related to soil and dust -- dust getting into the air ... then that's quite plausible," he says.