FRESNO, Calif. – California and federal public health officials say valley fever, a potentially lethal but often misdiagnosed disease infecting more and more people around the nation, has been on the rise as warming climates and drought have kicked up the dust that spreads it.

The fever has hit California’s agricultural heartland particularly hard in recent years, with incidence dramatically increasing in 2010 and 2011. The disease – which is prevalent in arid regions of the United States, Mexico, Central and South America – can be contracted by simply breathing in fungus-laced spores from dust disturbed by wind as well as human or animal activity.

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Catheters are used to treat some patients diagnosed with valley fever. The potentially lethal disease can be contracted by breathing in fungus-laced spores carried by dust. 2011 Associated Press file

The fungus is sensitive to environmental changes, experts say, and a hotter, drier climate has increased dust carrying the spores.

“Research has shown that when soil is dry and it is windy, more spores are likely to become airborne in endemic areas,” said Dr. Gil Chavez, Deputy Director of the Center for Infectious Diseases at the California Department of Public Health.

Long-standing concerns about valley fever were heightened last week when a federal health official ordered the transfer of more than 3,000 exceptionally vulnerable inmates from two San Joaquin Valley prisons where several dozen have died of the disease in recent years. A day later, state officials began investigating an outbreak in February that sickened 28 workers at two solar power plants under construction in San Luis Obispo County.

Although millions of residents in Central California face the threat of valley fever, experts say people who work in dusty fields or construction sites are most at risk, as are certain ethnic groups and those with weak immune systems. Newcomers and visitors passing through the region may also be more susceptible.

Nationwide, the number of valley fever cases rose by more than 850 percent from 1998 through 2011, according to the Centers for Disease Control and Prevention. In 2011, there were more than 20,400, with most cases reported in California and Arizona.

California public health officials say they are working to educate and train the public and doctors to recognize the illness.

The CDPH website and social media feature information and data about the disease, including advice to limit outdoor activities on dry, windy days.

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