Valley fever blowin’ on a hotter wind.
A dust storm blows across the highway in California's Central Valley. Photo by Christopher Taggart
15 April 2009
Hotter temps and more intense dust storms are propelling an endemic disease across the Southwest United States.
By Janice Arenofsky
Environmental Health News
and The Daily Climate
PHOENIX – It's high noon, and the 112-degree summer heat – up from a decade ago – stalks Arizona’s Sonoran Desert. By late afternoon, dark clouds threaten, and monsoon winds beat the earth into a mass of swirling sand. Thick walls of surface soil blind drivers on the Interstate.
Some health experts believe new weather conditions – hotter temperatures and more intense dust storms fueled by global warming – are creating a perfect storm for the transmission of coccidioidomycosis, also known as valley fever, a fungal disease endemic to the southwestern United States.
How do cocci spores infect the body? Propelled by winds, thousands of soil particles and cocci spherules are inhaled. People – particularly those older or immune-compromised – may experience flu-like symptoms that can turn into pneumonia. If the infection disseminates, the pathogens can target any organ – mostly the nervous system, skin, bones and joints – and become life threatening.
Each year, according to the American Academy of Microbiology, about 200,000 Americans contract valley fever, and 200 of them die. But some experts believe the disease is vastly underreported. Between 1991 and 1993, healthcare costs for valley fever exceeded $66 million, according to the Pan American Center for Human Ecology and Health.
The group Physicians for Social Responsibility says global warming will multiply the incidence due to increased airborne dust and sandstorms. Higher wind speeds and drought upped Arizona’s yearly count from 33 cases of valley fever per 100,000 in 1998 to 43 per 100,000 in 2001, said Dale Griffin of the U.S. Geological Survey in St. Petersburg, Fla.
The number of cases in Arizona more than quadrupled from 1997 to 2006, according to a Mayo Clinic study. During that same period, incidence rates in California jumped from 2.5 to 8.4 cases per 100,000 people.
Rising disease rates worry physician-researchers like Dr. John Galgiani, director of the Valley Fever Center for Excellence at the University of Arizona in Tucson. A cocci pioneer who has spent much of his career investigating the microscopic organisms, Galgiani knows their strong spore casings defend against high temperature, UV light and dust storms.
University of Arizona Geographer Andrew C. Comrie says Arizona’s precipitation and dust rates are good predictors of spikes in valley fever cases, and studies have reported that much of the variability between 1992 and 2005 was due to climate.
For Bill Sprigg, a climatologist at the University of Arizona, violations of federal air quality standards for particulates in the Southwest correlate to an overall higher incidence of valley fever. Other factors also might contribute to the higher rates of the disease, including population growth, improved reporting and greater numbers of people over age 65.
Forecasts of rising temperatures and moisture levels and alternating hot-dry and wet periods create a hospitable environment for cocci.
During the hot months, when other organisms die off on the surface, cocci survive several layers down. Then when rain falls, the fungus grows freely without competing organisms.
Comrie calls this his “grow and blow” theory. Higher temperatures not only enhance fungal growth, but also lead to the burn off of much vegetation. With fewer roots, leaves and branches holding back desert soil, storms can churn up more dust in wider areas of open space. Earthquakes and landslides also awaken millions of spores, dispersing the disease far and wide. After the 1994 Northridge earthquake in California, health professionals saw a sharp increase in new valley fever cases.
Comrie believes climate change may impact valley fever more than other infectious diseases.
“The key word is direct,” Comrie says. “Changes in temperature and precipitation will be felt directly in the soil where the fungus lives, in contrast to, say, West Nile virus, which would see second or third-order climate effects through mosquito vectors and bird hosts and their responses to climate.” Cocci neither requires an animal host nor does it possess “adaptation potential” – that is to say, in the absence of a vaccine or other curative agent, the spores win.
The steady rise in cases comes at a time when budget deficits and shifting state and national priorities frustrate researchers. Although the National Institutes of Health last year classified cocci as a bioterrorist weapon (Category C Priority Pathogen), its rare disease status and lack of a national market discourage pharmaceutical companies from developing a preventive vaccine or drug cure.
Experts believe fungi can travel long distances because the spore “housing” acts like a cocoon, protecting the fungus from environmental stresses. According to Andrew S. Goudie, of Oxford University in the United Kingdom, dust storms transport material over many “thousands of kilometers.” Indeed, satellite images show wind-borne dust originating from the Sahara and Gobi deserts of Africa and drifting to South America, the Caribbean and the southern United States. Researchers examining samples found more than 140 “hitchhiking” organisms.
Griffin, the USGS microbiologist, says one gram of desert soil can contain as many as one billion microorganisms. Any type of disturbance in soil – from natural forces such as wind or earthquakes or from man-initiated activities such as construction or off-road vehicles – could spread valley fever.
No evidence yet exists that cocci has trespassed beyond the boundaries of Arizona, California, Mexico and parts of Central and South America. But Sprigg and Comrie say this may be due more to budgetary constraints and the dearth of studies of dust-borne microorganisms. And since the symptoms of valley fever, such as fatigue, fever and lack of appetite, are common, misdiagnosis can easily occur and often does. Merry Buckley writes in the American Academy of Microbiology’s 2007 Tucson conference report that fungal diseases, such as valley fever, are often treated nonspecifically due to inconclusive testing results.
“Is the fungus in Africa?” Sprigg asks rhetorically. “Is it possible ‘pneumonia-like’ symptoms of troops returning from Iraq could be related to valley fever?” His point is simple: If health care professionals do not look for it, they are not likely to find it. So until a global inventory describing the various species and locations of the world’s fungi is carried out, no one can say for certain what the potential scope of cocci – or any other fungal infection – really might be.
One step toward mitigating dust-transported pathogens is the World Meteorological Organization’s plan to establish a sand dust warning system with nine regional centers. Meanwhile, a computer-based system launched by NASA in 2004 to forecast dust storms in the Southwest recently proved it can use land topography, the land-water ratio and surface roughness to correctly predict two out of three dust storms so as to warn Arizona residents.
Whether prior notice will lower the incidence of valley fever has not been determined. “There really is a lot more science that would be desirable in this area,” Comrie said.
Story © Janice Arenofsky
Photos of dust storms in California's Central Valley by Christopher Taggart, flickr.
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