Molecular detection of airborne Coccidioides in Tucson, Arizona

Abstract

Environmental surveillance of the soil-dwelling fungus Coccidioides is essential for the prevention of Valley fever, a disease primarily caused by inhalation of the arthroconidia. Methods for collecting and detecting Coccidioides in soil samples are currently in use by several laboratories; however, a method utilizing current air sampling technologies has not been formally demonstrated for the capture of airborne arthroconidia. In this study, we collected air/dust samples at two sites (Site A and Site B) in the endemic region of Tucson, Arizona, and tested a variety of air samplers and membrane matrices. We then employed a single-tube nested qPCR assay for molecular detection. At both sites, numerous soil samples (n = 10 at Site A and n = 24 at Site B) were collected and Coccidioides was detected in two samples (20%) at Site A and in eight samples (33%) at Site B. Of the 25 air/dust samples collected at both sites using five different air sampling methods, we detected Coccidioides in three samples from site B. All three samples were collected using a high-volume sampler with glass-fiber filters. In this report, we describe these methods and propose the use of these air sampling and molecular detection strategies for environmental surveillance of Coccidioides.

Relating coccidioidomycosis (valley fever) incidence to soil moisture conditions

“…Future analyses may allow for more comprehensive linkage between environmental conditions for Coccidioides growth and observed incidence by incorporating factors that account for dispersal and human exposure, ideally with methods to detect Coccidioides in air. Currently, laboratory detection of airborne Coccidioides DNA has only been successful with artificially created dust clouds [ Chow et al ., ]. However, future research is needed to enable this technology to be used for routine monitoring of Coccidioides in ambient air and to quantify spore count.…”

The mysterious desert dwellers:Coccidioides immitis and Coccidioides posadasii, causative fungal agents of coccidioidomycosis

“…propagules has been posited for many years, but has not been experimentally validated because has never been isolated from ambient dust and molecular detection is difficult [39][40][41][42][43][44][45][46][47][48]. Chow et al were able to detect airborne Coccidioides in a simulated dust storm with relative success, but detecting the fungus in actual dust storms is much more difficult [41]. Climate models show a drying trend in the endemic areas for Coccidioides that increases the likelihood for dust storms [49,50].…”

Coccidioides immitis and posadasii; A review of their biology, genomics, pathogenesis, and host immunity

“…It has been easier to grow C. immitis from the soil in the San Joaquin Valley of California in proximity to sites where humans are known to have been infected [7,11,14]. Detecting the organism from the atmosphere is even more difficult than finding it in the soil although recent development of new techniques may improve the sensitivity of detection of aerosolized fungal DNA [17]. …”