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Investigation of Occupational Exposures to Forestry Workers from Environmental Cryptococcus neoformans var. gattii
January 2006
| Principal Investigator: | Karen Bartlett (University of British Columbia) | |
| Co-investigators: |
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For more information about this study, please contact Dr. Karen Bartlett.
Issue
This project was designed to investigate occupational exposures to an environmental organism that can cause cryptococcosis, an emerging infectious disease in B.C.
The organism is an environmental yeast called Cryptococcus gattii (C. gattii ), previously found only in tropical and subtropical regions, but now present in treed areas on some parts of Vancouver Island. The first human cases of cryptococcosis in B.C. emerged in 1999. Since 1999, there have been approximately 25 new cases reported each year in BC, continuing to the present.
The study examined the prevalence and distribution of C. gattii in the Capital Region District (CDR) watershed compared with other parts of Vancouver Island, and assessed occupational exposures for working with and around trees in affected areas.
Key findings
- The highest percentage of tree clusters colonized by C. gattii was found around central Vancouver Island, with decreasing rates to the north and south. Only very low levels of C. gattii were found in the CRD watershed, and it is possible this may have been due to temporary contamination.
- In areas with colonized trees, the concentration of airborne C. gattii was highest in the dry summer months and lowest in the wet months of late fall, winter and early spring.
- Tasks such as limbing, chainsawing and chipping trees were found to release C. gattii into the air under dry conditions, when the organism was present.
- The study findings suggest that workers in some areas of BC have been exposed to C. gattii; however, more research is needed to understand the extent of exposures and potential health effects.
Objectives
- To evaluate the prevalence of C. gattii in trees, soil and air in the Capital Regional District (CRD) Watershed through environmental sampling.
- To examine the prevalence, distribution and seasonal variation of C. gattii found on Vancouver Island using existing data.
- To create job exposure matrices for woodland tasks.
- To pilot a questionnaire that gathers data on potential locations and durations of exposure and workers’ respiratory health and possible symptoms of cryptococcosis.
Method
Environmental sampling was conducted in the CRD watershed, including areas where workers would be conducting woodland maintenance tasks. Swabs were taken from the bark of a range of tree species, and soil and air samples were taken from the area close to the trees that were tested. Air samples were also taken during work procedures such as limbing, chainsawing and chipping to assess whether these tasks result in aerosolizing C. gattii.
Data from environmental sampling were examined in combination with existing data from other areas of Vancouver Island. The concentrations of air- and soil-borne C. gattii were determined and examined for seasonal variation and relationships with species of trees colonized. The concentration of airborne C. gattii was measured during limbing, chainsawing and chipping of trees.
A questionnaire was administered to workers from the CRD water department, as well as municipal and private arborists. Participants provided information related to locations and durations of exposure, as well as respiratory and other symptoms related to cryptococcosis.
Results
C. gattii -infected trees varied by species and placement. Colonization rates ranged from 5 – 22%, and included coniferous (Cedar, Thuja; Douglas fir, Pseudotsuga; Pine, Pinus), evergreen (Arbutus, A. menziesii), and deciduous trees (Alder, Alnus; Garry Oak, Quercus; and Maple, Acer).
The highest percentage of C. gattii -colonized trees were found in clusters around Central Vancouver Island (Parksville, 30%), with the concentration of colonized trees decreasing to the north (Courtenay, 6%) and south ( Victoria, 3%). Airborne and soil concentrations of C. gattii correlated closely with positive-tree clusters.
The highest concentrations of airborne C. gattii were found in the summer (June and July), which were also the driest months. In contrast, soil concentrations appeared to be highest in September and October.
Woodland tasks involving limbing, chainsawing or chipping created aerosols of C. gattii when the tree was colonized and environmental conditions were dry.
The number of positive samples found in the entire watershed was low (1 of 105 soil samples; 1 of 173 tree samples). In addition, the only two positive cultures were recovered from a road that permits logging trucks, and the C. gattii may have been transiently present rather than truly colonized. These sites will be re-examined.
Conclusions
The results of this study suggest that woodland workers in certain areas of BC have been exposed to C. gattii , and that exposure will depend on the colonized status of the trees and soil. In addition, wet weather reduces the levels of airborne concentration of the organism.
The researchers recommend that employers and workers be informed about the risks of exposure to the organism and the symptoms of cryptococcosis.
Future directions
The questionnaire data on workers’ exposure and symptoms will be used to design a larger study to examine the work practices and potential exposures of outdoor workers in greater detail. The questionnaire will be revised based on information gained through this study.
Further research is also needed to determine if workers develop protective antibodies to the organism, or if the possibility exists of asymptomatic disease, the development of a carrier state, or if reactivation of latent infection may occur.
Further, ongoing environmental sampling is also needed to determine whether the levels of C. gattii in BC are increasing, decreasing or stable.
Publications
Duncan C , Stephen C, Lester S and Bartlett, KH. 2005 Sub-clinical infection and asymptomatic carriage of Cryptococcus gattii in dogs and cats during an outbreak of cryptococcosis. Accepted Medical Mycology January 2005.
Kidd S, Hagen F, Tscharke M, Huynh M, Bartlett KH, Fyfe, M, MacDougall L, Boekhout T, Kwon-Chung KJ, Meyer W. 2004. A rare genotype of Cryptococcus gattii caused the cryptococcosis outbreak on Vancouver Island ( British Columbia, Canada). Proceedings of the National Academy of Sciences 101(49): 17258-17263.
Extended (printed) abstracts from scientific conferences
Bartlett , KH , Fyfe, M, MacDougall, L, Duncan, C, and Kidd, S. 2005. A new ecological niche for the pathogenic yeast, Cryptococcus neoformans var. gattii, in a temperate climate zone. Fifth International Conference on Bioaerosols, Fungi, Bacteria, Mycotoxins and Human Health. Saratoga Springs, NY. September 10 – 12, 2003 pp 315-322.
Bartlett , KH, Fyfe, M, MacDougall, L, Duncan, C, Mak, S, Kidd, S. Cryptococcus gattii, a tropical pathogen emerging in a temperate climate zone. 16 th conference on biometeorology and aerobiology. August 23-27, 2004, Vancouver BC.
Bartlett , KH, Fyfe, M, MacDougall, L, Mak, S, Kidd, S. 2004 Cryptococcus gattii, temporary visitor or landed immigrant? Can J Plant Path 27:1.
Conference papers presented at scientific meetings
Adrian Hingston , Hugh Davies, Helen Ward, Karen Bartlett. Evaluation of exposure to Cryptococcus neoformans var. gattii among arborists and landscapers.” AIHCE, Anaheim, CA, May 2005.
Kidd, SE, Guo, H, Bartlett, KH, Kronstad, JW, Xu, J. Gene genealogies indicate multiple recent migrations and a clonal propagation of at least two distinct evolutionary lineages of Cryptococcus gattii isolates in British Columbia. Sixth International Conference on Cryptococcus and Cryptococcosis, Boston, MA June 24 – 28, 2005.
Invited presentations at scientific and public meetings
Bartlett, KH. 6 th International Conference on Cryptococcus and Cryptococcosis: “Canadian Cryptococcus gattii – temporary visa or landed immigrant?” Boston, MA June 24-28, 2005.
Bartlett, KH. International Conference 2005: Collaboration to Solve Environmental Problems in Asia/Pacific Region. “Microbe Hunting: a curious case of Cryptococcus.” June 3-4, 2005. Seoul, South Korea.
Bartlett, KH. Celebrate Research! Public presentation at UBC Robson Square March 9, 2005. “Microbe Hunters: a curious case of Cryptococcus.”
Bartlett, KH. Respiratory and Infectious Disease Journal Club, Vancouver Island Health Authority. “Environmental sources of Cryptococcus gattii on Vancouver Island.” February 15, 2005, Grand Pacific Hotel, Victoria, BC.
Bartlett, KH. Mount Arrowsmith Biosphere Reserve lecture series. “When you go out in the woods today, you’re sure of a big surprise!” January 26, 2005. Parksville, BC.
Interviews and news stories
February 10, 2005: Nanaimo Bulletin. Interview re: Cryptococcus gattii in the environment on Vancouver Island.
January 28, 2005. Parksville-Qualicum Beach News. Interview re: public lecture on Cryptococcus on Vancouver Island.
December 9, 2004. Ladysmith Chronicle. Interview re: local cases of cryptococcosis in Ladysmith, BC.
December 2, 2004. Country Wide on Country Canada Channel ( Winnipeg). Re: Cryptococcus gattii on Vancouver Island.
December 1, 2004: Weather Network. Televised interview re: Cryptococcus gattii on Vancouver Island.
November 25, 2004. CHQR News Radio, Calgary. Interview on Morning Show re: Cryptococcus gattii on Vancouver Island.
November 19, 2004: CanWest News Service. Follow-up on emergent pathogenic yeast, Cryptococcus gattii on Vancouver Island (Kidd et al. PNAS paper released).
Additional information
Hingston, Adrian. 2006. Occupational Exposures to Cryptococcus gattii: Evaluation of exposure to C. gattii among arborists and CRD Watershed employees on Vancouver Island. MSc Thesis (Occupational and Environmental Hygiene) University of British Columbia.Griffiths, Andrea. 2006. Assessing exposure to Cryptococcus gattii. MSc Thesis (Occupational and Environmental Hygiene) University of British Columbia.
Duncan C, Stephen C, Lester S and Bartlett, KH. 2005 Follow-up study of dogs and cats with asymptomatic Cryptococcus gattii infection or nasal colonization. Medical Mycology 43: 663-666
Duncan, C, Schwantje, H, Stephen, C, Campbell, J, Bartlett K. Cryptococcus gattii in wildlife of Vancouver Island, BC, Canada. Accepted Journal Wildlife Diseases.
Kidd, SE, Guo, H, Bartlett, KH, Kronstad, JW, Xu, J. 2005. Comparative gene genealogies indicate that two clonal lineages of Cryptococcus gattii in British Columbia resemble strains from other geographical areas. Eucaryotic Cell 4: 1629-1638.