HBO's series "The Last of Us" has increased awareness around fungal infections—and one infection typically found in dry, arid climates has the potential to become more prevalent with climate change.

What you need to know about 'Valley fever'

When spores of the Coccidioides immitis fungus or Coccidioides posadasii fungus are inhaled, it can cause an illness known as coccidioidomycosis or "Valley fever."

According to the Mayo Clinic, these fungi are typically found in the soil in Arizona, Nevada, Utah, New Mexico, California, Texas, and Washington. However, most cases are reported in Arizona and California, according to CDC.

Over the past decade, cases have been on the rise, with over 20,000 infections reported in 2019. However, experts believe that figure underestimates the actual number of cases. Most people who are infected experience mild illness that may cause few or no symptoms, leaving many cases unreported.

Typically, symptoms mirror a respiratory virus infection, with common symptoms like fever, cough, tiredness, headache, chills, muscle aches and pains, and rashes.

In roughly 5% to 10% of cases, coccidioidomycosis causes more serious illness that can lead to chronic—and potentially deadly—forms of the disease. Most serious cases occur among individuals with weakened immune systems.

Manish Butte, professor and division chief of immunology, allergy, and rheumatology in the department of pediatrics at the University of California, Los Angeles noted that there is a small subset of the population where the fungus "spreads rapidly and destructively throughout the body," consuming flesh for nutrition.

"If it spreads to the brain or spinal cord, about 40% of the people die," Butte said. The entire process can take up to two weeks from the time of exposure. According to CDC, around 200 people die from "Valley fever" each year.

As deaths from various fungal infections continue to grow in the United States, many fans of HBO's new show "The Last of Us" expressed concern that "Valley fever" mirrors the contagious fungal infection featured in the show, which sends the world into a deadly pandemic. But experts have noted that "Valley fever" is not transmitted from person to person or between people and animals. The illness "can't spread from the lungs" between people and animals, according to CDC.

While most acute infections can be treated using antifungal medications like fluconazole, Butte noted that it can sometimes be difficult to determine when to use it.

According to Butte, fungal infections are difficult to detect through simple x-rays and the only diagnostic testing available is a blood test that can detect antibodies. 

Clinicians can sometimes mistake fungal infections for a viral or bacterial infections and use antibiotics to treat patients, said Paris Salazar-Hamm, a researcher at the University of New Mexico School of Medicine.

"You wipe out the bacterial flora (with the antibiotic), allowing the fungal infection to grow and it makes it worse," Salazar-Hamm said.

"Fungi are more closely related to humans than they are to bacteria," she added. "Targets for fungal drugs have negative side effects for human cells."

Why is 'Valley fever' becoming more prevalent?

In a 2019 study published in GeoHealth, researchers predicted that climate change would cause the endemic region of the fungus to spread north to dry western states, including Idaho, Wyoming, Montana, Nebraska, South Dakota, and North Dakota.

In a high-warming scenario, this could increase the size of the affected area by 50% by 2100, while making the fungi prevalent in 17 states instead of 12.

"Fungal pathogens are a group that get vastly overlooked and Valley fever is an interesting model because it's associated with the climate," said Paris Salazar-Hamm.

Previously, the average temperature of the human body was too hot for most fungi to thrive. However, research suggests that, as global temperatures have increased, some fungi might be adapting to become more resilient to heat stress, including conditions within the human body.

"As fungi are exposed to more consistent elevated temperatures, there's a real possibility that certain fungi that were previously harmless suddenly become potential pathogens," said Peter Pappas, an infectious-disease specialist at the University of Alabama at Birmingham. (Rodriguez, USA Today, 2/1; Tilley, Daily Mail, 2/1; Johncox, Click On Detroit, 1/31; Mosbergen, Wall Street Journal, 2/1)