Cryptococcus gattii in the United States: Genotypic Diversity of Human and Veterinary Isolates

Abstract

Background Cryptococcus gattii infections are being reported in the United States (US) with increasing frequency. Initially, US reports were primarily associated with an ongoing C . gattii outbreak in the Pacific Northwest (PNW) states of Washington and Oregon, starting in 2004. However, reports of C . gattii infections in patients from other US states have been increasing since 2009. Whether this is due to increasing frequency of disease, greater recognition within the clinical community, or both is currently unknown.Methodology/Principal FindingsDuring 2005–2013, a total of 273 C . gattii isolates from human and veterinary sources in 16 US states were collected. Of these, 214 (78%) were from the Pacific Northwest (PNW) and comprised primarily the clonal C . gattii genotypes VGIIa (64%), VGIIc (21%) and VGIIb (9%). The 59 isolates from outside the PNW were predominantly molecular types VGIII (44%) and VGI (41%). Genotyping using multilocus sequence typing revealed small clusters, including a cluster of VGI isolates from the southeastern US, and an unrelated cluster of VGI isolates and a large cluster of VGIII isolates from California. Most of the isolates were mating type MATα, including all of the VGII isolates, but one VGI and three VGIII isolates were mating type MATa .Conclusions/SignificanceWe provide the most comprehensive report to date of genotypic diversity of US C . gattii isolates both inside and outside of the PNW. C . gattii may have multiple endemic regions in the US, including a previously-unrecognized endemic region in the southeast. Regional clusters exist both in California and the Southeastern US. VGII strains associated with the PNW outbreak do not appear to have spread substantially beyond the PNW.

Antifungal Drug Susceptibility and Phylogenetic Diversity among Cryptococcus Isolates from Dogs and Cats in North America

“…Other sequence types identified in our study have been also reported before from Asia (ST5 and ST32), Africa (ST5, ST23, ST39, and ST43), and the United States (ST32) (40)(41)(42)(43)(44)(45). Molecular type VNI, VNII, VGI, and VGII isolates from dogs and cats in this study had sequence types that were identical or closely related to those of the reference VGI and VGII strains, respectively, supporting the more clonal relationship of these populations as described previously (15,16).…”

“…However, infections with C. gattii molecular type VGIII were recently identified in human patients with HIV/AIDS from southern California (16). A lower number of molecular type VGIII isolates have been isolated from humans in other states, including those in the Pacific Northwest, the south, Michigan, and Alaska (15), although the travel history of many of the infected individuals in these states was unknown. Analysis of VGIII isolates infecting humans in the United States has shown a genetically diverse population of isolates that includes both mating types ␣ and a and that can be separated into VGIIIa and VGIIIb subclusters (15,16).…”

“…Dendrograms showing the genetic relationships among C. gattii isolates and among C. neoformans isolates were constructed using a software package (MEGA 5.05; Center for Evolutionary Medicine and Informatics, Tempe, AZ) based on maximum likelihood analysis of the concatenated seven ISHAM consensus MLST loci. Additional C. gattii strains included in the MLST analysis are listed in Table S1 in the supplemental material (15,28,(32)(33)(34)(35)(36)(37).…”

“…C. gattii strains that belong to molecular type VGII can be further categorized into a large number of subtypes. Of those VGIIa, VGIIb, and VGIIc have been implicated in disease in immunocompetent humans, cats, dogs, and other animal species in British Columbia and the Pacific Northwest of the United States (3,(13)(14)(15)). An epidemiological study of dogs and cats with cryptococcosis in California showed that cats were most often infected with C. gattii molecular type VGIII, whereas dogs were more likely to be infected with C. neoformans, possibly reflecting host differences in susceptibility (6).…”

“…Infections with strains of molecular type VGIII in dogs have not yet been described, but C. gattii molecular type VGIII has emerged as a cause of disease in immunocompromised humans in southern California (16), and molecular type VGIII was the predominant C. gattii molecular type identified in humans from California in another recent report. Two VGIII subclusters have been identified in these individuals based on the results of multilocus sequence typing, VGIIIa and VGIIIb (15,16). In eastern Australia, molecular type VGI predominates among C. gattii isolates as a cause of disease in cats (17).…”