For most people who are suffering from fever, cough and fatigue, the likely culprits are cold, flu or COVID-19. 

But for those living in the southwestern U.S., the symptoms could point to Valley fever — and some scientists predict that this illness eventually could spread to other regions. 

Named after the San Joaquin Valley in California, Valley fever is an infection caused by breathing in the spores of a fungus called Coccidioides, which originates in the soil. 

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Southern Arizona and Southern California have the highest volume of cases, per the Centers of Disease Control and Prevention (CDC) — but the disease is also prevalent in New Mexico, Nevada, Utah, Texas and parts of Washington State.

As of 2019, Valley fever cases topped 20,000 nationwide, the CDC reported.

Reported cases tripled in that state between 2014 and 2018, according to the California Department for Public Health.

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Dr. George Thompson, a professor at UC Davis Health and co-director of the Center for Valley fever in Sacramento, told Fox News Digital about the ramp-up in cases. 

"We have seen a gradual increase in cases over the last five years, and a greater number of patients are coming into our clinic for diagnosis and treatment," he said.

While geographic location heightens the overall risk of contracting Valley fever, the CDC notes that certain groups are more vulnerable.

These include people 60 years of age and older; those who have weakened immune systems as a result of certain diseases or medical conditions; pregnant women; people with diabetes; and people who are Black or Filipino.

Symptoms of Valley fever tend to mimic those seen in patients with COVID-19, experts say.

"Some [people] may have a fever, chills or fatigue, or just feel generally unwell," Thompson of UC Davis Health said.

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However, he said he does see some severe cases where patients experience respiratory illness. 

Thompson estimated that for 1%-3% of people, the infection will leave the lungs and travel to other parts of the body — which can lead to meningitis. 

Although it’s rare, people outside the high-risk groups can experience severe effects from Valley fever.

On New Year’s Day in 2012, Rob Purdie of California, then 38, woke up with a terrible headache and nausea. 

"It felt like the worst hangover of my life — but I hadn’t had a single drink the night before," he told Fox News Digital. 

Doctors chalked up his symptoms to a sinus infection, but after two rounds of antibiotics, Purdie felt no better.

The next diagnosis was cluster headaches, yet a new medication didn’t help. 

When Purdie started experiencing double vision, he ended up in the Kern Valley ER. There, a spinal tap led to a diagnosis of meningitis caused by Valley fever. 

The spores of the fungus had spread from his lungs to his brain and nervous system, a potentially fatal condition.

That was just the beginning of years of medications and treatments, many with life-altering side effects, he said.

More than a decade later, Purdie lives with the lingering effects of disseminated coccidioidal meningitis caused by Valley fever. 

Every few weeks, he receives an antifungal treatment that is injected directly into his brain through a port in his head, he told Fox News Digital.

Today, Purdie works as a patient and program coordinator at Kern Medical’s Valley Fever Institute, the same facility that helped save his life. He is passionate about advocating for other patients, raising awareness of the disease and lobbying for public health and research funding.

In 2019, a study by Morgan Gorris — which was published in GeoHealth, a journal focused on environmental and health sciences research — suggested that climate change could trigger an expansion of Valley fever into northwestern states, including Idaho, Wyoming, Montana, Nebraska, South Dakota and North Dakota. 

"At first, I was skeptical," said Dr. Thompson of California. "But I’ve recently heard about new cases emerging in Nebraska and even Missouri, so I think it’s in the realm of possibility."

Valley fever cases are expected to arrive in northern Utah and eastern Colorado by 2035, according to the study. Gorris, the study's author, also predicts that the disease will become endemic in Nebraska, southeastern Montana, southern Idaho and South Dakota by 2065, and that it could arrive in northern Montana and North Dakota by 2095.

Other research has linked the rising Valley fever cases to an increase in dust storms. Another recent GeoHealth study by Daniel Q. Tong, a scientist and professor at George Mason University in Virginia, found that dust storms in the Southwest have risen by 240% between the 1990s and 2000s, followed by an 800% spike in Valley fever cases between 2001 and 2011.

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Purdie, for his part, believes that Valley fever could become more widespread amid changing climate patterns and population growth. 

"Valley fever likes undisturbed soil — so as people continue to populate more arid, dry and less developed areas, there will likely be more interaction with it," he said.

While there is not yet a vaccine for Valley fever, Dr. Thompson is optimistic about progress toward that goal. He pointed to three vaccines currently in development, including one that has been successfully tested with dogs. 

The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, recently announced $4.5 million in funding to support research toward diagnostics, therapeutics and vaccines for the disease.

In the meantime, Thompson often treats Valley fever patients with antifungal medications such as Fluconazole and Itraconazole.

Since the fungus that causes Valley fever lives in the soil, infection is often "hobby-related," Thompson said. He said he sees many cases among people who are in archeology or who spend a lot of time outdoors. 

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For those in high-risk groups, the doctor recommends avoiding construction sites or areas where soil is often stirred up into the air. 

People can also wear an N95 respirator, a type of high-quality mask, to minimize exposure in dusty areas.

Thompson stressed the importance of early diagnosis and treatment. 

A blood test sent to a lab can confirm a current or prior infection of Valley fever, and a chest X-ray or CT scan can detect cases of pneumonia, according to the CDC.