Characterization of Environmental Sources of the Human and Animal Pathogen Cryptococcus gattii in British Columbia, Canada, and the Pacific Northwest of the United States

Abstract

Cryptococcus gattii has recently emerged as a primary pathogen of humans and wild and domesticated animals in British Columbia, particularly on Vancouver Island. C. gattii infections are typically infections of the pulmonary and/or the central nervous system, and the incidence of infection in British Columbia is currently the highest reported globally. Prior to this emergence, the environmental distribution of and the extent of colonization by C. gattii in British Columbia were unknown. We characterized the environmental sources and potential determinants of colonization in British Columbia. C. gattii was isolated from tree surfaces, soil, air, freshwater, and seawater, and no seasonal prevalence was observed. The C. gattii concentrations in air samples were significantly higher during the warm, dry summer months, although potentially infectious propagules (<3.3 m in diameter) were present throughout the year. Positive samples were obtained from many different areas of British Columbia, and some locations were colonization "hot spots." C. gattii was generally isolated from acidic soil, and geographic differences in soil pH may influence the extent of colonization. C. gattii soil colonization also was associated with low moisture and low organic carbon contents. Most of the C. gattii isolates recovered belonged to the VGIIa genetic subtype; however, sympatric colonization by the VGIIb strain was observed at most locations. At one sampling site, VGIIa, VGIIb, VGI, and the Cryptococcus neoformans serotype AD hybrid all were coisolated. Our findings indicate extensive colonization by C. gattii within British Columbia and highlight an expansion of the ecological niche of this pathogen.

Primer aislamiento ambiental de Cryptococcus gattii de serotipo B, en Cúcuta, Colombia

“…Another factor that influenced the isolation of C. gattii from soil is the fact that all samples were recovered near to the soil surface, which is in agreement with other reports, where C. gattii has been recovered in the first 15 cm of the humic layer of soil, where the conditions of temperature, moisture, and nutrient requirements, are enough for the colonization of the fungus (32).…”

“…grubii from the same place, like the co-distribution of different genotypes or serotypes found in previous studies (27,28,32) could suggest a related introduction and dispersal mechanisms or synergistic colonization considering that in some cases the populations could be very complex.…”

The Search for the Natural Habitat of Cryptococcus gattii

“…The distribution pattern of E. camaldulensis has been associated with the relatively high proportion of C. gattii infections among rural aboriginals, compared to other areas where C. gattii was known from clinical sources [8]. However, shortly after this finding, Ellis and Pfeiffer, as well as other Australian investigators isolated C. gattii from a wide variety of Eucalyptus species and Syncarpia glomulifera, which is also a native Australian tree species [7,9]. Eucalyptus trees have been exported from Australia to many countries, especially those with a subtropical or tropical climate, which is the preferred environment for Eucalyptus trees [7][8][9].…”

“…However, shortly after this finding, Ellis and Pfeiffer, as well as other Australian investigators isolated C. gattii from a wide variety of Eucalyptus species and Syncarpia glomulifera, which is also a native Australian tree species [7,9]. Eucalyptus trees have been exported from Australia to many countries, especially those with a subtropical or tropical climate, which is the preferred environment for Eucalyptus trees [7][8][9]. It has been speculated that the export of Eucalyptus seeds and trees had contributed to the dispersal of C. gattii [7,8].…”

Cryptococcus neoformans isolation from swallow (Hirundo rustica) excreta in Iran

“…Among these, C. neoformans and C. gattii are pathogenic. Following its first identification in nature from peach juice samples 24 , the major environmental sources of C. neoformans have been shown to be either soil contaminated with avian droppings (C. neoformans) or eucalyptus trees and decaying wood forming hollows in living trees (C. gattii) 4,11,12,26 .…”