Heavy rain + high temps means greater risk of Valley Fever

The fungal disease can cause lung damage and in some cases spread to other organs.
The coccidioides fungus, which starts out as a mold found in soil, can cause Valley Fever.
The coccidioides fungus, which starts out as a mold found in soil, can cause Valley Fever.
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4 min read

The California Department of Public Health is warning of potential increased risk of Valley Fever statewide after winter’s heavy rains and summer’s increasingly hot temperatures.

“Valley Fever is an urgent health crisis because of climate change,” says UCLA Health clinical microbiologist Shaun Yang, PhD.

Valley Fever is a fungal disease that can cause respiratory symptoms and, in some people, severe pulmonary infection and chronic lung damage. California cases were previously concentrated in the central part of the state, but have been rising statewide in recent years, tripling between 2014 and 2018.

Also known as coccidioidomycosis or cocci, Valley Fever is caused by a dimorphic fungus — one that exists as both mold and yeast, Dr. Yang says.

It starts out as a mold found in the soils of the desert Southwest. The mold produces infectious spores, which can be carried by dust and stirred up by agriculture and construction when the weather is dry. When people inhale the spores or dust, the spores germinate. Once inside the human body, however, they cease to grow as mold and instead become a pathogenic yeast

“It’s a different kind of morphology,” Dr. Yang says. “That’s why we call it a dimorphic fungus.”

Risk to lungs and other organs

Many people infected with Valley Fever are asymptomatic, he says, but some people can develop severe pulmonary infection, which can be chronic and difficult to treat.

The illness can also spread outside the lungs to infect other organs, including the brain. In 2019, 190 Californians were diagnosed with disseminated cocci after the illness spread to their skin, bones or brain. The mortality rate is high when the infection spreads beyond the lungs, says Manish Butte, MD, PhD, who in 2022 received an $8.4 million grant from the National Institute of Allergy and Infectious Diseases to improve diagnosis and treatment of Valley Fever by studying what can go wrong with the immune system’s lines of defense.

“California probably spends around a billion dollars a year taking care of patients with Valley Fever and disseminated disease,” says Dr. Butte, the E. Richard Stiehm Professor of Pediatric Allergy, Immunology and Rheumatology at the David Geffen School of Medicine at UCLA. “But the treatments today resemble those developed in the 1990s, and we still dont have a good idea which patients will get really sick and which ones will have milder disease.”

People with compromised immune systems — including organ-transplant recipients, people with HIV and people receiving chemotherapy — are at greater risk of developing disseminated disease, Dr. Butte says. Pregnant people are also at higher risk of poor outcomes from Valley Fever, Dr. Yang adds.

Researchers don’t know why some people, even those who were previously healthy and not immunocompromised, develop serious or disseminated disease from Valley Fever.

“It’s not always that if you are very healthy, you will not get severe disease,” Dr. Yang says. “We have yet to find out what exactly is the host factor that can lead to more severe infection.”

Researchers at UCLA Health are working closely with colleagues at UC San Diego, the Valley Fever Institute in Kern County and the UC Davis Valley Fever Center of Excellence, Dr. Butte says.

At UCLA Health, infectious diseases physicians work together to care for patients with severe coccidioidomycosis, offering groundbreaking therapies that aren’t available anywhere else.

Increased spread is likely

Heavy rains over the winter made cases of Valley Fever more likely this summer. The wet winter encouraged growth of mold and spores while the dry summer has made it easier for those spores to float around in the air, where they can be unwittingly inhaled.

“That factor of being both wet and then dry actually is the perfect setting for a lot of cocci to flow around,” Dr. Yang says.

As the climate becomes hotter and drier, cocci is spreading from areas where it’s traditionally been found — Central California, Arizona, New Mexico and Texas — ever northward.

“Maybe in a few decades, half of the United States will be endemic for cocci,” Dr. Yang says. “Because of climate change and global warming, this endemic fungus will become more widespread and cause more infections.”

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