As discussed previously, the reported prevalences of Campylobacter spp. in dogs and cats has varied widely between studies worldwide. Data for New Zealand dogs and cats are limited. One study performed in the Manawatu sentinel site, screened 530 dog and 64 cat faecal samples. C. jejuni prevalence rates of 4.5% and 4.7% have been reported for dogs and cats, respectively (356, 450). The study design did not allow epidemiological investigations with regard to factors associated with faecal carriage due to the anonymous sampling scheme and only focused on the identification of C. jejuni. This knowledge gap is addressed in this thesis with two studies:
• A cross-sectional study of Campylobacter spp. in the urban population of dogs
and cats in Manawatu.
• A cross-sectional study of Campylobacter spp. in the working farm dog
population in Manawatu.
In order to additionally investigate the potential exposure of humans with pet food- related sources, a cross-sectional pilot survey of raw meat pet diets for the presence of Campylobacter spp. was also performed. Pet diets sampled included commercially available raw pet food products in Palmerston North and home-kill frozen sheep and beef meat as part of the working farm dogs’ diet.
A recent survey of human diagnostic laboratory practices in New Zealand has shown that the vast majority of laboratories use standard culture methods whereas only one uses an immunoenzymatic method for detection of Campylobacter spp. (53). The report has shown none of the culture methods employed to be suitable for detection of non-jejuni/coli Campylobacter spp., which raises a suspicion for the potential underestimation of emerging Campylobacter spp. in New Zealand patients. With regard to the immunoenzymatic methods, the MedLab Central laboratories in
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Manawatu use a faecal antigen test, the ProSpecTTM Campylobacter Microplate Assay (Remel Inc., USA) for the detection of Campylobacter species. The assay has been developed for the detection of C. jejuni and C. coli but two independent studies have shown the assay has a limited capability for detection of C. upsaliensis though data was insufficient to explain the limitations (128, 129). The mEpiLab collaborates
with MedLab Central laboratories for the purposes of source attribution studies in Manawatu. The positive samples by the antigen assay are sent to mEpiLab where a
culture method is used for isolation and subsequent molecular typing of isolates. A review of mEpiLab’s records has shown that between 16 and 23% (reported in 2010
and 2011, respectively) of positive samples by the above assay were culture negative in our laboratory. This discrepancy in test results could be explained by the delay in the processing of samples, which might result in the presence of dead or viable-but-not culturable (VBNC) bacteria in faecal samples. Unlike microbiological culture, non-culture methods, such as antigen and nucleic acid-based methods have the ability to detect dead and VBNC bacteria. This serves as a potential advantage over the culture methods but also questions the specificity of these methods due to the potential reaction with “free-floating” cellular components in faeces resulting in a false positive test result. Alternatively, the discrepancy in the above test results might be explained by the antigen assay having detected non-jejuni/coli Campylobacter spp. that have failed to be isolated by the culture method used in mEpiLab, which has
been optimised for detection of C. jejuni and C. coli. This issue formed the next aim of this thesis:
• Evaluation of analytical sensitivity of ProSpecTTM Campylobacter Microplate
Assay for the detection of C. upsaliensis, C. helveticus and C. hyointestinalis in human spiked faecal samples.
Insects have been established as a reliable model for studying the innate immune system because, unlike the adaptive immune system, there is a high degree of structural and functional homology of the innate immune responses between insects and mammals (451). Galleria mellonella has been shown as a suitable model for studying several bacterial and fungal pathogens and recently also for C. jejuni (452).
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Emerging Campylobacter spp. have not been studied in this manner and to ensure validity of this approach comparison with the known pathogen, C. jejuni, was included. The isolates of C. upsaliensis and C. helveticus obtained through cross- sectional studies were used for this next aim:
• Experimental study of pathogenic potential of C. upsaliensis and C. helveticus
compared to C. jejuni using an insect model of disease, the larvae of the Greater Wax moth, Galleria mellonella.
As reviewed, there is a lack of genomic data for many Campylobacter spp. Other than C. jejuni and C. coli. In the early stages of this thesis project there were only two whole genome sequences of C. upsaliensis published and none at all for C. helveticus. The main interests were to explore the general features of the genomes and functional profiles and, in particular, pathogenicity markers, which formed the last aim using isolates from the cross-sectional studies:
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