ECOLOGICAL SOURCES AND TRANSMISSION CYCLES OF THERMOPHILIC CAMPYLOBACTER AND RELATIONSHIPS WITH THE EPIDEMIOLOGY OF HUMAN CAMPYLOBACTERIOSIS

Thi Thu Hong Nguyen (2010). ECOLOGICAL SOURCES AND TRANSMISSION CYCLES OF THERMOPHILIC CAMPYLOBACTER AND RELATIONSHIPS WITH THE EPIDEMIOLOGY OF HUMAN CAMPYLOBACTERIOSIS PhD Thesis, School of Veterinary Science, The University of Queensland.

       
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Author Thi Thu Hong Nguyen
Thesis Title ECOLOGICAL SOURCES AND TRANSMISSION CYCLES OF THERMOPHILIC CAMPYLOBACTER AND RELATIONSHIPS WITH THE EPIDEMIOLOGY OF HUMAN CAMPYLOBACTERIOSIS
School, Centre or Institute School of Veterinary Science
Institution The University of Queensland
Publication date 2010-01
Thesis type PhD Thesis
Supervisor Rowland Cobbold
Myat Kyaw-Tanner
Jennifer Seddon
Total pages 387
Total colour pages 12
Total black and white pages 375
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary The transmission of Campylobacter from its various sources to humans is a potentially complicated ecological process with multiple hosts and routes involved. An understanding of transmission routes of thermophilic Campylobacter would help to prevent human campylobacteriosis. The transmission cycles of thermophilic Campylobacter among various ecological sources and humans have been relatively poorly investigated, especially in non-temperate countries like Australia. The aim of this research was to investigate ecological sources and transmission cycles of thermophilic Campylobacter among various potential sources and to examine their relationships with human campylobacteriosis in Brisbane (Australia). Thermophilic Campylobacter were widespread among a wide range of ecological sources in an urban area in South East Brisbane (Queensland, Australia) through a 12 month longitudinal survey. C. jejuni was the predominant species in beef and lamb offal isolates, while C. coli was predominant in pork, waters, chicken meat, soils, and wild birds. C. upsaliensis was the major species for pet samples. Human Campylobacter data and isolates which were temporally and geographically matched were collected in parallel to the longitudinal survey. The speciation of randomly chosen human Campylobacter isolates showed that C. jejuni and C. coli accounted for 69.5 and 28.7% of strains, respectively. The possible impacts of four climatic factors on the prevalence of thermophilic Campylobacter and the two main species in ecological sources and the number of human Campylobacter infections per month were investigated. Results showed that there were significant associations of the proportions of ecological samples positive for Campylobacter and climatic factors. However, these associations varied depending on examination of Campylobacter in general or at species levels. A significant temporal association between daily temperatures, relative humidity and rainfall, with appropriate lag effects, and the number of human Campylobacter infections per month was also reported. Temporal associations between Campylobacter prevalence in ecological samples and monthly human campylobacteriosis cases were also determined. Results demonstrated a positive correlation between the sample prevalence for Campylobacter in pork, chicken meat and dogs and monthly human campylobacteriosis cases. Further study at the species level revealed that C. jejuni prevalence in pets was strongly associated with the number of human C. jejuni infections per month, while C. coli prevalence in soils was positively correlated with the number of human C. coli infections per month. Genotypic associations between 200 Campylobacter isolates from humans and ecological sources which were temporally and geographically matched were investigated using flaA-Restriction Fragment Length Polymorphism (flaA-RFLP) and Multilocus Sequence Typing (MLST). The findings revealed a difference in grouping patterns for the two major zoonotic species. For C. jejuni, human isolates appeared to be related to isolates from a greater diversity of sources representing foods, animals and the environment, while for C. coli, human isolates tended to be more closely related to food isolates. The distribution of six key virulence markers was determined and compared between Campylobacter isolates from humans and ecological sources. Results showed that all isolates had flaA and cadF genes regardless of origin and species, while 98, 99, 97 and 49% of isolates had cdtA, cdtB, cdtC and iam genes, respectively. 98% of C. coli isolates carried all six principle virulence markers and the distribution of virulence markers in C. coli isolates from foods was similar to those from humans. The epidemiology of antimicrobial resistance of 200 isolates from humans and ecological sources was also investigated. Apart from ampicillin, the resistance of Campylobacter isolates to erythromycin, tetracycline and ciprofloxacin was only observed in clinical isolates, but not in ecological sources, with the exception of one ciprofloxacin resistant water isolate. Significant differences in resistance rates between C. jejuni and C. coli were observed for erythromycin and ampicillin. In conclusion, thermophilic Campylobacter were isolated among various ecological sources including foods, animals and environmental samples such as waters and soils. Apart from foods, temporal as well as genotypic associations between Campylobacter strains were observed for humans and other ecological sources. These findings indicate the need to design a broad and comprehensive control strategy for human campylobacteriosis that considers the impact of climatic conditions, multiplicity of transmission pathways, and the interactions of humans with various potential Campylobacter sources in the greater environment. C. coli were isolated at relatively higher frequencies from both ecological sources and human campylobacteriosis cases than expected. This finding underlines the significance of optimising isolation techniques to recover non-jejuni species and for more routine speciation of Campylobacter in clinical laboratories. There were differences in the ecology of the two major Campylobacter species in terms of associations with climatic factors, and with human Campylobacter isolates by genotypic, virulence marker distribution and antimicrobial resistance profiles. These findings suggest a need for different control strategies for human campylobacteriosis based on the associated species. It also highlights the need to further investigate the ecology of these organisms at both general and species levels.
Keyword Campylobacter
microbiology
infectious disease ecology
zoonosis
transmission cycles
human campylobacteriosis
Additional Notes Pages in colour: 52, 139, 142, 143, 144, 176, 177, 184, 185, 186, 189, 241 Pages in landscape: 61, 62, 66, 71, 89, 94, 97, 98, 118, 146, 147, 148, 149, 150, 173, 184, 185, 189, 191, 196, 198, 199, 216, 217, 220, 221, 222, 237, 241, 243, 340, 387.

 
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Created: Wed, 29 Sep 2010, 13:24:57 EST by Ms Thi Thu Hong Nguyen on behalf of Library - Information Access Service