Understanding a Desert Menace

Millions of residents and visitors traveling to the American Southwest each year may not know that the air they breathe could lead to a severe lung infection.

In desert soils of Arizona, California, Nevada, New Mexico, Texas and Utah, a fungus resides that causes Valley fever – also known as coccidioidomycosis or "desert rheumatism." In the wake of summer rains, the fungus releases its spores and – with wind and people stirring up dirt in endemic regions – there's a higher risk of inhaling the air-solvent microns, says Douglas Lake, an associate professor in the School of Life Sciences at Arizona State University.

Valley fever often goes underdiagnosed because the initial symptoms that present themselves one to three weeks after exposure are similar to a cold or flu, and the majority of people infected may never know they had it, Lake says. According to the Centers for Disease Control and Prevention, approximately 10,000 cases of Valley fever are reported in the U.S. each year, yet it's been estimated that closer to 150,000 actually occur.

"People that spend the wintertime here in Arizona or maybe in California might inhale spores from the fungus and then get the disease," Lake says. "If they go back to Michigan or Wisconsin or wherever they're from and they don't tell their doctor that they've been in an area where this fungus is present, then the diagnoses might be delayed or even missed."

Common testing for the fungus also requires an immune response that may not be triggered until several weeks to months after exposure, and a delayed diagnosis could lead to patients being misdiagnosed and inappropriately treated while the fungal infection continues to grow and cause more severe issues. Valley fever is most common in older adults, while pregnant women, those with weakened immune systems, people with diabetes, African-Americans and Filipinos may be at higher risk of a severe case, according to the CDC.

Lake recently spoke to U.S. News about the prevalence of Valley fever in the U.S., as well as research endeavors to diagnose it sooner. The interview has been edited for length and clarity.

Valley fever is nothing new in the Southwest. But how big of a public health issue is this fungal disease?

Between 95 and 97 percent of the infections that are reported are in Arizona and California. The endemic regions probably extend into Mexico, because the fungus doesn't care if it grows below the United States, but the endemic area is mainly in the Central Valley in California and in Phoenix and Tucson. It also extends into West Texas and throughout New Mexico and southern Utah, and there's been a few isolated cases found in the state of Washington. There are about 10,000 reported cases per year, but those are cases where people seek medical attention. It's thought that there's probably 120,000 to 150,000 infections per year. Many people don't seek medical attention – they'll be sick for a little bit, and then their immune systems will take over and they'll get over it.

The diagnosis of Valley fever is very difficult. Patients may have a pneumonia that could be viral, bacterial or fungal. Two-thirds of the time it's viral or bacterial, but in our endemic region 30 percent of pneumonias are Valley fever. Current blood tests for Valley fever rely on patients to make an immune response against the fungus, but this fungus is tricky and many people who are otherwise healthy won't make antibodies against the fungus even though they are acutely ill.

Is Valley fever deadly on its own?

Most people, about 60 percent of people, will not seek medical attention, and they'll just get a pulmonary infection, so a lung infection – it'll be like a cold or a flu and then they'll just get over it. But 40 percent of people will get a disease that makes them go to the doctor, and probably 10 percent of those people will get a very severe infection and they'll have to go on antifungal drugs for a long period of time. And for probably a lower percentage, like 1 percent of those 10 percent, it can be a lethal infection – it can be lethal on its own. If your immune system is compromised, whether you're taking a medication that compromises your immune system or it's people walking around that are immunosuppressed like HIV patients, things like that, they're at an increased risk. But by living in the endemic region, just by breathing, you're at risk.

You're currently working with the Mayo Clinic on developing a test that can detect the fungus in patients sooner. Could you tell me about that research?

My laboratory is working with Mayo Clinic, and specifically I'm working with Tom Grys, the director of the microbiology laboratory at Mayo Clinic-Arizona, and we're developing a test to detect the bits and pieces of the fungus in urine.

When people inhale fungal spores from the desert soil, the fungal spores are just the right size to germinate in the terminal bronchioles in your lung. And then, in a very different environment in your lung, they start to grow in a different form than they grow out in the soil in the desert. When they grow in your lung, they're called spherules, and what happens is that they shed a lot of components while they're growing – it's like how people shed skin cells all the time. So the fungus sheds its outer coat, and we're detecting bits and pieces of that outer coat in urine.

The test isn't ready yet – we're still developing the test, but the distinct advantage of this test is that it won't rely on patients' immune systems. The fungus is tricky – it doesn't seem to stimulate a strong immune response early in the infection. Our new test can detect components of the fungus while patients are acutely ill even if their immune systems haven't recognized the infection yet. With continued funding, we're hopeful that in a couple years we'll be able to make the test available, but it's going to take funding to move this test into the clinic.

According to CDC data, there was a huge number of cases reported in 2011. The number of reported cases then dropped, but seems to have crept up more in recent years. Is there an explanation for the high number of cases in 2011?

There are people doing climate studies and epidemiological studies, but we don't actually know. There's some evidence that the fungus is seasonal. For example, after the rains come in the summertime here, then the fungus can grow out in the dirt, and then once it grows, if the soil is disturbed and there's a little bit of dust, people can inhale the spores from the dust.

People also are outside more when it starts to cool off after the summer rains.

We probably don't have a good explanation yet for why, for example, California reported over 5,000 cases in 2016, which is up from 3,000 previously. It's an understudied fungus; it's an understudied disease.

Do weather events like the recent haboob in Phoenix relate to Valley fever's prevalence?

It's difficult to say, because when the dust storms happen, the wind takes the dust from the surface, and if there is some fungus on the surface of the desert soil, then it might be solvent to the air, getting in those dust storms. But the fungus generally grows between 4 and 16 inches down into the soil. So we don't necessarily see a huge increase in cases after dust storms. It's multifactorial. The dust storms are scary-looking, but we don't see a huge number of cases after dust storms.

The scientific evidence is more that when the rains come, the fungus grows a little bit more in the soil. And then as the rains go and things dry up and it's also cooling off then, people are out more. And if people are out and hiking through the desert, for example, and stirring up dirt, then there's a better chance for them to be exposed and infected.