Over the past two decades, several fungal outbreaks have occurred, including the high-profile ‘Vancouver Island’ and ‘Pacific Northwest’ outbreaks, caused by Cryptococcus gattii, which has affected hundreds of otherwise healthy humans and animals. Over the same time period, C. gattii was the cause of several additional case clusters at localities outside of the tropical and subtropical climate zones where the species normally occurs. In every case, the causative agent belongs to a previously rare genotype of C. gattii called AFLP6/VGII, but the origin of the outbreak clades remains enigmatic. Here we used phylogenetic and recombination analyses, based on AFLP and multiple MLST datasets, and coalescence gene genealogy to demonstrate that these outbreaks have arisen from a highly-recombining C. gattii population in the native rainforest of Northern Brazil. Thus the modern virulent C. gattii AFLP6/VGII outbreak lineages derived from mating events in South America and then dispersed to temperate regions where they cause serious infections in humans and animals.
C. gattii may be spread through soil disturbances, wind, water, distribution of tree and soil byproducts, and human movement.
Recent Cryptococcus gattii infections in humans and animals without travel history to Vancouver Island, as well as environmental isolations of the organism in other areas of the Pacific Northwest, led to an investigation of potential dispersal mechanisms. Longitudinal analysis of C. gattii presence in trees and soil showed patterns of permanent, intermittent, and transient colonization, reflecting C. gattii population dynamics once the pathogen is introduced to a new site. Systematic sampling showed C. gattii was associated with high-traffic locations. In addition, C. gattii was isolated from the wheel wells of vehicles on Vancouver Island and the mainland and on footwear, consistent with anthropogenic dispersal of the organism. Increased levels of airborne C. gattii were detected during forestry and municipal activities such as wood chipping, the byproducts of which are frequently used in park landscaping. C. gattii dispersal by these mechanisms may be a useful model for other emerging pathogens.
Cryptococcus gattii; dispersal; colonization; British Columbia; Pacific Northwest; research
Infectious fungi are among a broad group of microbial pathogens that has and continues to emerge concomitantly due to the global AIDS pandemic as well as an overall increase of patients with compromised immune systems. In addition, many pathogens have been emerging and reemerging, causing disease in both individuals who have an identifiable immune defect and those who do not. The fungal pathogen Cryptococcus gattii can infect individuals with and without an identifiable immune defect, with a broad geographic range including both endemic areas and emerging outbreak regions. Infections in patients and animals can be severe and often fatal if untreated. We review the molecular epidemiology, population structure, clinical manifestations, and ecological niche of this emerging pathogen.
Fungal infections; Cryptococcosis; Emerging outbreak; Pulmonary disease; Meningitis
Health care facility ventilation design greatly affects disease transmission by aerosols.
The desire to control infection in hospitals and at the same time to reduce their carbon
footprint motivates the use of unconventional solutions for building design and associated control measures. This paper considers indoor sources and types of infectious aerosols, and pathogen viability and infectivity behaviors in response to environmental conditions. Aerosol dispersion, heat and mass transfer, deposition in the respiratory tract, and infection mechanisms are discussed, with an emphasis on experimental and modeling approaches. Key building design parameters are described that include types of ventilation systems (mixing, displacement, natural and hybrid), air exchange rate, temperature and relative humidity, air flow distribution structure, occupancy, engineered disinfection of air (filtration and UV radiation), and architectural programming (source and activity management) for health care facilities. The paper describes major findings and suggests future research needs in methods for ventilation design of health
care facilities to prevent airborne infection risk.
The in vitro susceptibilities of a worldwide collection of 350 Cryptococcus gattii isolates to seven antifungal drugs, including the new triazole isavuconazole, were tested. With amplified fragment length polymorphism (AFLP) fingerprinting, human, veterinary, and environmental C. gattii isolates were subdivided into seven AFLP genotypes, including the interspecies hybrids AFLP8 and AFLP9. The majority of clinical isolates (n = 215) comprised genotypes AFLP4 (n = 76) and AFLP6 (n = 103). The clinical AFLP6 isolates had significantly higher geometric mean MICs for flucytosine and fluconazole than the clinical AFLP4 isolates. Of the seven antifungal compounds examined in this study, isavuconazole had the lowest MIC90 (0.125 μg/ml) for all C. gattii isolates, followed by a 1 log2 dilution step increase (MIC90, 0.25 μg/ml) for itraconazole, voriconazole, and posaconazole. Amphotericin B had an acceptable MIC90 of 0.5 μg/ml, but fluconazole and flucytosine had relatively high MIC90s of 8 μg/ml.
This organism should be recognized as an emerging pathogen in the United States.
Cryptococcus gattii has emerged as a human and animal pathogen in the Pacific Northwest. First recognized on Vancouver Island, British Columbia, Canada, it now involves mainland British Columbia, and Washington and Oregon in the United States. In Canada, the incidence of disease has been one of the highest worldwide. In the United States, lack of cryptococcal species identification and case surveillance limit our knowledge of C. gattii epidemiology. Infections in the Pacific Northwest are caused by multiple genotypes, but the major strain is genetically novel and may have emerged recently in association with unique mating or environmental changes. C. gattii disease affects immunocompromised and immunocompetent persons, causing substantial illness and death. Successful management requires an aggressive medical and surgical approach and consideration of potentially variable antifungal drug susceptibilities. We summarize the study results of a group of investigators and review current knowledge with the goal of increasing awareness and highlighting areas where further knowledge is required.
Cryptococcus gattii; cryptococcosis; fungi; Vancouver Island; Pacific northwest; Canada; United States; synopsis
The relatively uncommon fungal pathogen Cryptococcus gattii recently emerged as a significant cause of cryptococcal disease in human and animals in the Pacific Northwest of North America. Although genetic studies indicated its possible presence in the Pacific Northwest for more than 30 years, C. gattii as an etiological agent was largely unknown in this region prior to 1999. The recent emergence may have been encouraged by changing conditions of climate or land use and/or host susceptibility, and predictive ecological niche modeling indicates a potentially wider spread. C. gattii can survive wide climatic variations and colonize the environment in tropical, subtropical, temperate, and dry climates. Long-term climate changes, such as the significantly elevated global temperature in the last 100 years, influence patterns of disease among plants and animals and create niche microclimates habitable by emerging pathogens. C. gattii may have exploited such a hitherto unrecognized but clement environment in the Pacific Northwest to provide a wider exposure and risk of infection to human and animal populations.
We report a case of cryptococcosis due to C. gattii which appears to have been acquired in the Puget Sound region, Washington State. Genotyping confirmed identity to the predominant Vancouver Island genotype. This is the first documented case of human disease by the major Vancouver Island emergence strain acquired within the United States.
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 μm 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.
Cryptococcus gattii, emergent on Vancouver Island, British Columbia (BC), Canada, in 1999, was detected during 2003–2005 in 3 persons and 8 animals that did not travel to Vancouver Island during the incubation period; positive environmental samples were detected in areas outside Vancouver Island. All clinical and environmental isolates found in BC were genotypically consistent with Vancouver Island strains. In addition, local acquisition was detected in 3 cats in Washington and 2 persons in Oregon. The molecular profiles of Oregon isolates differed from those found in BC and Washington. Although some microclimates of the Pacific Northwest are similar to those on Vancouver Island, C. gattii concentrations in off-island environments were typically lower, and human cases without Vancouver Island contact have not continued to occur. This suggests that C. gattii may not be permanently colonized in off-island locations.
Cryptococcus gattii; population surveillance; environmental exposure; British Columbia; detection; Pacific Northwest; research
Cryptococcus gattii has recently emerged as a pathogen of humans and animals in the temperate climate of Vancouver Island, British Columbia (B.C.). The majority (∼95%) of the isolates from the island belong to the VGII molecular type, and the remainder belong to the VGI molecular type. The goals of this study were to compare patterns of molecular variation among C. gattii isolates from B.C. with those from different areas of the world and to investigate the population structure using a comparative gene genealogy approach. Our results indicate that the C. gattii population in B.C. comprises at least two divergent lineages, corresponding to previously identified VGI and VGII molecular types. The genealogical analysis of strains suggested a predominantly clonal population structure among B.C. isolates, while there was evidence for sexual recombination between different molecular types on a global scale. We found no geographic pattern of strain relationships, and nucleotide sequence comparisons revealed that genotypes among isolates from B.C. were also present among isolates from other areas of the world, indicating extensive strain dispersal. The nucleotide sequence diversity among isolates from B.C. was similar to that among isolates from other areas of the world.
Mammalian cathelicidins are a class of innate antimicrobial peptides isolated from leukocytes and epithelial cells that aid host defense against bacterial infections. Synthetic analogs of cathelicidins offer the promise of potent broad-spectrum antimicrobial efficacy. We developed a combined lung infection and ex vivo whole-blood assay model to characterize the toxicity and efficacy of synthetic cathelicidin-derived peptides. Male C57BL/6 mice were administered saline or Klebsiella pneumoniae by intratracheal instillation. Five hours later, the Klebsiella-infected mice were instilled with saline, tobramycin (1 mg/kg of body weight or 10 mg/kg), novispirin G10 (0.4 mg/kg), or a combination of tobramycin (1 mg/kg) and G10 (0.4 mg/kg). At 24 h, bronchoalveolar lavage fluid (BAL) was collected for analysis of culturable bacteria and for markers of inflammation and lung toxicity. Blood samples were analyzed for circulating cytokines. Recovery of Klebsiella from the lung, recruitment of neutrophils, and production of interleukin-6 (IL-6) in BAL samples were highly correlated (r = 0.68 and 0.84, respectively; P < 0.01). Animals treated with G10 or G10 plus tobramycin had increased hemoglobin (P < 0.001) and protein (P < 0.001) levels compared to those for Klebsiella-infected or tobramycin-alone-treated animals. The levels of circulating IL-6 in mice infected with Klebsiella were 1000- to 10,000-fold higher than in the noninfected controls. The highest levels of IL-6 were measured in mice given G10 alone or in combination with tobramycin. These studies demonstrated that G10 was relatively nontoxic in saline-treated mice but was highly toxic in mice infected with Klebsiella. This finding establishes the importance of investigating candidate antimicrobial agents in an in vivo infection model.
Ornamental aquarium plants were demonstrated to carry as many as 108 viable mesophilic bacteria per g. Gram-negative organisms predominated among the 19 genera of bacteria identified. Pseudomonas aeruginosa was readily isolated from 53% of the samples tested.
The seven-membered ring compounds tropilidine and tropone were shown to be bacteriostatic and bactericidal for a wide range of bacterial species.