Valley Fever an occupational hazard for geoscientists

by Sara E. Pratt
Thursday, August 7, 2014

Valley Fever is a sometimes-fatal disease caused by a soilborne fungus contracted by inhaling spores in airborne dust. Arizona, where this dust storm occurred in 2011, is a highly endemic area. Credit: ©Alan Stark, CC BY-SA 2.0.

Geoscientists should take precautions against contracting Valley Fever — a sometimes-fatal infection with no known cure and no vaccine that is caused by a soilborne fungus, said James A. Jacobs, a California-based consulting hydrogeologist, at the annual meeting of the American Institute of Professional Geologists last year.

The disease, known medically as coccidioidomycosis, is contracted through inhalation of spores of two species of fungus of the genus Coccidioides. They are known to thrive in the hot, dry soils of the southwestern U.S., Mexico and Central and South America. However, recent reports of infections far outside the endemic area indicate the fungus is either spreading or becoming active in new areas.

Coccidioides spores can become aerosolized through soil disturbances caused by construction, gardening and landscaping, as well as natural events like dust storms, earthquakes, landslides and wildfires. They lodge deep in the lungs and can spread to other parts of the body via the bloodstream.

The spores can initially trigger flu-like and other symptoms, including fever, headache, cough, breathing difficulties, fatigue, weight loss, muscle and joint pain and a skin rash. This can cause the disease to be overlooked or misdiagnosed, especially in areas where physicians are unfamiliar with it.

In 2010 and 2011, three acute cases of coccidioidomycosis occurred in Washington state, far outside the endemic area. None of the patients — a 12-year-old boy who often played in a dusty canyon, a 15-year-old boy who had crashed his ATV on a dirt track and cut his knee, and a 58-year-old construction excavator with advanced liver disease — had visited endemic areas.

“Given the patients' lack of recent travel, coccidioidomycosis was not suspected, leading to delays in diagnosis and appropriate therapy,” reported epidemiologist Nicola Marsden-Haug of the Washington State Department of Health and colleagues in the journal Clinical Infectious Diseases. “Clinicians should be aware of this possibility and consider the diagnosis.”

Those clinicians include veterinarians. All vertebrates are susceptible to the disease, says research geologist Mark Bultman, who co-authored the 2000 U.S. Geological Survey (USGS) report “Operational Guidelines for Geological Fieldwork in Areas Endemic for Coccidioidomycosis.” Bultman, who lives in the heart of the endemic area in Tucson, Ariz., speaks from personal experience, having lost his dog to side effects of the treatment for Valley Fever several years ago.

According to the Centers for Disease Control and Prevention (CDC), roughly 20,000 new cases of Valley Fever are diagnosed each year, mainly in Arizona and California, and infections usually peak in September. However, epidemiological models estimate that as many as 150,000 people are being infected each year. Between 1991 and 2011, the infection rate rose by a factor of 10, the causes of which are being studied. Most cases are asymptomatic infections that resolve without medication, and up to 60 percent of people living in endemic areas have developed some immune resistance.

In the early days of researching the disease, before Coccidioides' virulence was fully understood, biologists often contracted the disease through accidental lab exposures. However, several earth scientists have also contracted it through exposures in the field.

In April 1940, seven Stanford University students on a biology field trip in California’s San Joaquin Valley contracted the disease after one student dug up a dusty squirrel hole that a rattlesnake had entered. More recently, in June 2001, 10 members of a team of National Park Service archaeologists and student volunteers contracted the illness while working at a site in Dinosaur National Monument in northeastern Utah — more than 120 kilometers north of the endemic area. This marked the first time coccidioidomycosis was diagnosed outside the endemic area. The crew had sifted dirt looking for artifacts; none had worn a dust mask. Eight were hospitalized and treated with antifungal medicine.

The National Park Service and USGS investigated the worksite, which was composed of bedonite, a fine, alkaline soil conducive to Coccidioides spores. The state and local health departments made recommendations to minimize soil disturbance and dust inhalation, including wetting the soil and wearing masks, and work at the site resumed in late September, after which one more employee came down with Valley Fever. Subsequently, the National Park Service advised visitors to Dinosaur National Monument to stay on maintained trails to minimize soil disturbance and warnings are now posted when wind conditions raise dust levels.

The soil fungus has likely existed for millennia, but has only become a problem recently with increased population growth, development and soil disturbance in the endemic area. The ways that the soil fungus can spread aren’t fully known; it can be carried by the wind or on a hiker’s boot. In the case of Dinosaur National Monument, which is located in what was once the northern part of the Anasazi Empire, it is possible the fungus was transported north along ancient trade routes, Bultman says.

Little is also known about the fungus' preferred geology and how a changing climate might affect its spread. Previous findings seem to show it is less prevalent in granitic soils than other types of soil, says USGS geochemist Geoff Plumlee, who studies the health effects of earth materials. However, “in terms of linking properties of the soil fungus to soil chemistry,” he says, “there’s still a lot more work to be done.”

Research also continues to develop a vaccine for Valley Fever.

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