Characterization of environmental sources of the human and animal pathogen Cryptococcus gattii in British Columbia, Canada, and the Pacific Northwest of 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 (
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.
It has been over a decade since Cryptococcus gattii was first recognized as the causative organism of an outbreak of cryptococcosis on Vancouver Island, British Columbia. A number of novel observations have been associated with the study of this emergent pathogen. A novel genotype of C. gattii, VGIIa was described as the major genotype associated with clinical disease. Minor genotypes, VGIIb and VGI, are also responsible for disease in British Columbians, in both human and animal populations. The clinical major genotype VGIIa and minor genotype VGIIb are identical to C. gattii isolated from the environment of Vancouver Island. There is more heterogeneity in VGI, and a clear association with the environment is not apparent. Between 1999 and 2010, there have been 281 cases of C. gattii cryptococcosis. Risk factors for infection are reported to be age greater than 50 years, history of smoking, corticosteroid use, HIV infection, and history of cancer or chronic lung disease. The major C. gattii genotype VGIIa is as virulent in mice as the model Cryptococcus, H99 C. neoformans, although the outbreak strain produces a less protective inflammatory response in C57BL/6 mice. The minor genotype VGIIb is significantly less virulent in mouse models. Cryptococcus gattii is found associated with native trees and soil on Vancouver Island. Transiently positive isolations have been made from air and water. An ecological niche for this organism is associated within a limited biogeoclimatic zone characterized by daily average winter temperatures above freezing.
Cryptococcus gattii emerged on Vancouver Island, British Columbia (BC), Canada, in 1999, causing human and animal illness. Environmental sampling for C.gattii in southwestern BC has isolated the fungal organism from native vegetation, soil, air, and water.
Our aim was to help public health officials in BC delineate where C.gattii is currently established and forecast areas that could support C.gattii in the future. We also examined the utility of ecological niche modeling (ENM) based on human and animal C.gattii disease surveillance data.
We performed ENM using the Genetic Algorithm for Rule-set Prediction (GARP) to predict the optimal and potential ecological niche areas of C.gattii in BC. Human and animal surveillance and environmental sampling data were used to build and test the models based on 15 predictor environmental data layers.
ENM provided very accurate predictions (> 98% accuracy, p-value
The purpose of this study was to describe the geographic distribution and model the ecological niche for Borrelia burgdorferi (Johnson, Schmidt, Hyde, Steigerwaldt & Brenner), Ixodes pacificus (Cooley & Kohls), and Ixodes angustus (Neumann), the bacterium and primary tick vectors for Lyme disease, in British Columbia (BC), Canada. We employed a landscape epidemiology approach using geographic information systems mapping and ecological niche modeling (Genetic Algorithm for Rule-set Prediction) to identify geographical areas of disease transmission risk. Forecasted optimal ecological niche areas for B. burgdorferi are focused along the coast of Vancouver Island, the southwestern coast of the BC mainland, and in valley systems of interior BC roughly along and below the N51 degree line of latitude. These findings have been used to increase public and physician awareness of Lyme disease risk, and prioritize future field sampling for ticks in BC.
Lyme disease (LD) is rare in British Columbia (BC) and, despite being a reportable condition since 1994, may be underreported. Here we review all provincial laboratory and clinical databases to determine the number of LD cases reported in BC from 1997 to 2008. We analyzed demographic characteristics of LD cases and used capture-recapture methodology to estimate the true number of cases in BC for this period. From 1997 to 2008, 93 confirmed cases of LD were reported in BC. Conservative capture-recapture estimates place the true number of LD cases in BC during this period at 142 (95% confidence interval: 111-224), indicating up to 40% underreporting of this rare disease. Despite this underreporting, BC continues to have low endemic risk of LD. Strategies are needed to increase both physician awareness and the use of preventive measures in the BC population, including for those traveling to other endemic areas.
West Nile virus (WNv) has recently emerged as a health threat to the North American population. After the initial disease outbreak in New York City in 1999, WNv has spread widely and quickly across North America to every contiguous American state and Canadian province, with the exceptions of British Columbia (BC), Prince Edward Island and Newfoundland. In this study we develop models of mosquito population dynamics for Culex tarsalis and C. pipiens, and create a spatial risk assessment of WNv prior to its arrival in BC by creating a raster-based mosquito abundance model using basic geographic and temperature data. Among the parameters included in the model are spatial factors determined from the locations of BC Centre for Disease Control mosquito traps (e.g., distance of the trap from the closest wetland or lake), while other parameters were obtained from the literature. Factors not considered in the current assessment but which could influence the results are also discussed.
Since the model performs much better for C. tarsalis than for C. pipiens, the risk assessment is carried out using the output of C. tarsalis model. The result of the spatially-explicit mosquito abundance model indicates that the Okanagan Valley, the Thompson Region, Greater Vancouver, the Fraser Valley and southeastern Vancouver Island have the highest potential abundance of the mosquitoes. After including human population data, Greater Vancouver, due to its high population density, increases in significance relative to the other areas.
Creating a raster-based mosquito abundance map enabled us to quantitatively evaluate WNv risk throughout BC and to identify the areas of greatest potential risk, prior to WNv introduction. In producing the map important gaps in our knowledge related to mosquito ecology in BC were identified, as well, it became evident that increased efforts in bird and mosquito surveillance are required if more accurate models and maps are to be produced. Access to real time climatic data is the key for developing a real time early warning system for forecasting vector borne disease outbreaks, while including social factors is important when producing a detailed assessment in urban areas.
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Cites: J Am Mosq Control Assoc. 2000 Mar;16(1):22-710757487
The understanding of how tuberculosis is transmitted can be improved by combining DNA fingerprinting of Mycobacterium tuberculosis with conventional epidemiologic methods. We used such techniques to determine the predictors of clustering of identical isolates from tuberculosis patients in Vancouver.
We used the restriction fragment length polymorphism (RFLP) technique and, if necessary, spoligotyping to determine DNA patterns of M. tuberculosis isolates from all patients with newly diagnosed tuberculosis in Greater Vancouver reported to the Division of Tuberculosis Control from January 1995 to March 1999. Isolates were considered to be part of a cluster if they had an identical DNA pattern. We also collected demographic and epidemiologic data. Predictors associated with being in a cluster were analyzed in a multivariate logistic regression model.
Isolates from 793 patients (430 men) were identified; 137 (17.3%) were considered to be in clusters. After adjustment for multiple potential predictors, we found that the following patients were more likely to be part of a cluster: Canadian-born Aboriginals (v. foreign-born patients) (adjusted odds ratio [OR] 6.0, 95% confidence interval [CI] 3.0-11.7), Canadian-born non-Aboriginals (v. foreign-born patients) (adjusted OR 3.6, 95% CI 2.1-6.3), and injection drug users (v. patients who did not inject drugs) (adjusted OR 3.9, 95% CI 1.9-8.1). Patients with a prior history of tuberculosis were less likely to be part of a cluster than were patients with no history of tuberculosis (adjusted OR 0.3, 95% CI 0.1-0.8).
Our findings indicate the need to target groups at high risk of tuberculosis more aggressively to prevent transmission and to treat latent infection. DNA fingerprinting may be a useful adjunct to conventional epidemiologic methods to monitor the transmission of tuberculosis in an inner-city setting.
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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.
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In 2009, an expansion of West Nile virus (WNV) into the Canadian province of British Columbia was detected. Two locally acquired cases of infection in humans and 3 cases of infection in horses were detected by ELISA and plaque-reduction neutralization tests. Ten positive mosquito pools were detected by reverse transcription PCR. Most WNV activity in British Columbia in 2009 occurred in the hot and dry southern Okanagan Valley. Virus establishment and amplification in this region was likely facilitated by above average nightly temperatures and a rapid accumulation of degree-days in late summer. Estimated exposure dates for humans and initial detection of WNV-positive mosquitoes occurred concurrently with a late summer increase in Culex tarsalis mosquitoes (which spread western equine encephalitis) in the southern Okanagan Valley. The conditions present during this range expansion suggest that temperature and Cx. tarsalis mosquito abundance may be limiting factors for WNV transmission in this portion of the Pacific Northwest.
