The Outbreak of Cryptococcus gattii in Western North America: Epidemiology and Clinical Issues

Abstract

Over the previous decade, we observed the emergence of the fungal pathogen, Cryptococcus gattii, as a cause of disease in humans and animals in a temperate climate. This outbreak, first documented on Vancouver Island, has since expanded throughout Western North America, with non–travel-associated cases now in British Columbia, Washington, Oregon, and California. Additionally, a secondary outbreak, originating in and still restricted to Oregon, has also occurred. During the past several years, several studies detailing molecular typing, virulence, antifungal susceptibilities, epidemiology, and clinical issues have been published. These studies begin to address the complex dynamics of this novel emergence of a rare and fatal fungus, outline clinical characteristics of human cases, and also opened several new areas that should be explored in the upcoming years.

Cryptococcus gattii Infections

“…Single cases of infection have also been reported in the United States, including New England (85,243,247), New Mexico (272), and Florida (253); Europe (91,95,106,245); Asia, including Japan and Singapore (227,246,249); and South America (223,256). Most recently, Harris et al reported 25 cases, inclusive of previously described patients (247,253) diagnosed between 2009 and 2012, from Montana, Alabama, California, Hawaii, and Michigan; none of these patients had traveled to areas of C. gattii endemicity (251).…”

“…The Canadian and Pacific Northwest outbreak strains are all of mating type ␣ and comprise two subtypes of the major molecular type VGII/AFLP6, namely, VGIIa/AFLP6A and VGIIb/AFLP6B (38). As well as in British Columbia, Canada, molecular type VGII has now been reported in the United States (68,85,86) (Fig. 4).…”

“…Table 4 summarizes the pertinent epidemiological and clinical features in case series involving three or more patients. In addition, a number of reviews, editorials, and book chapters with substantive discussion on C. gattii clinical epidemiology and infection in humans have been published since 2000 (39,85,122,(254)(255)(256)(257)(258)(259)(260)(261)(262)(263)(264)(265).…”

The cryptic sexual strategies of human fungal pathogens

“…Unisexual mating between two closely related α isolates of C. gattii is thought to have produced a highly virulent strain responsible for an ongoing outbreak that initiated on Vancouver Island, British Columbia 35,103 . The outbreak is associated with high mortality rates (>25%) in both healthy and immunosuppressed individuals, as well as in domestic and wild animals 103 .…”

“…The outbreak is associated with high mortality rates (>25%) in both healthy and immunosuppressed individuals, as well as in domestic and wild animals 103 . Since the first cases were reported, the outbreak has spread into the Pacific Northwest of the US and Canada 36,103,104 . Numerous genotypes are responsible for these infections but the major genotype, VGIIa, is the presumed product of a homothallic mating event between closely related isolates of the VGII type 35 .…”