Paper No. 7
Presentation Time: 3:15 PM
CHARACTERISTICS AND CONTROLS OF THE ENDEMIC ZONES (EZ) OF COCCIDIOIDES SPP. (ETIOLOGICAL AGENTS OF COCCIDIOIDOMYCOSIS)
FISHER, Frederick S., Geosciences, University of Arizona, 520 N. Park Ave, Suite 355, Tucson, AZ 85719, JOHNSON, Suzanne M., School of Medicine, University of California, Davis, One Shields Ave, Tupper Hall, Rm 3146, Davis, CA 95616-8645 and PAPPAGIANIS, Demosthenes, School of Medicine, University of California, Davis, One Shields Ave, Tupper Hall, Davis, CA 95616-8645, ffisher@email.arizona.edu
The two most important factors that define endemic zones of
Coccidioides are soil temperature and soil moisture. Clearly these factors are related to the air temperature and precipitation respectively. However many other factors affect soil temperatures; such as soil color, vegetation types and densities, sun aspect, thermal conductivity, depth in soil profile, and soil moisture content. All
Coccidioides growth sites where we have measured soil temperatures throughout the southwestern U. S. are within soils classified as hyperthermic arid, thermic arid, or thermic semi-arid. Soils, at depths of 20 - 30cm and within a temperature range of 10
0 to 40
0 C, are most favorable for the growth of
Coccidioides. Precipitation is the main factor determining the moisture supply needed for
Coccidioides growth. However, the amount of water that infiltrates the soil to depths where
Coccidioides may be present depends on the amount lost to runoff, surface roughness, soil texture, preexisting water content, and the soil content of salt, clay, and organic material. Moisture in the upper 20 - 30 cm of the soil profile is essential for the growth of
Coccidioides; however, the actual amount required, is unknown at this time.
Soils from archeological digs, construction, domestic excavations, paleontology sites, landslide areas, and an animal pen display a wide diversity of physical, chemical, and biological attributes. These locations are noteworthy in that they are all areas where humans, dogs and/or monkeys, were infected by Coccidioides. The most striking observation from examination of these sites is their diversity and lack of any one or group of factors that might be definitive of the presence of Coccidioides. Factors measured include, electrical conductivity, salinity, selected anions, texture, mineralogy, vegetation, and geomorphology. No particular grass, shrub, or forb is definitive. Very fine sand and silt are abundant in all of the Coccidioides bearing soils. Overwhelmingly, the primary method of infection is by the inhalation of Coccidioides spores. Increased soil erosion and changing wind patterns due to drought and climate changes within and adjacent to EZ bear monitoring, because of the potential of large unexposed populations outside of known EZ being infected by wind borne arthroconidia.
