The epidemiology of campylobacter infection in dogs in the context of the risk of infection to humans

Campylobacter spp. are the most common causes of bacterial gastroenteritis in humans worldwide, and although poultry and cattle are considered major sources of Campylobacter spp. , infection has also been associated with dogs. In order to investigate the potential zoonotic risk to humans, dog faeces were examined for the presence of Campylobacter spp. from several different dog populations including; vet-visiting, boarding, rescue and hunt dogs. The Campylobacter spp. prevalence, and species distribution was determined for all studies, and some studies were analysed for possible risk factors for Campylobacter spp. carriage in dogs. Longitudinal studies were carried out on kennelled dogs to investigate shedding patterns, and possible transmission. All C. jejuni, and 41 C. upsaliensis isolates from these studies underwent multilocus sequence typing (MLST), along with nine C. upsaliensis isolates originating from human clinical cases, in order to identify possible sources of infection, and assess the potential zoonotic risk to humans. Additionally a pilot study was performed to annotate a plasmid as part of a C. upsaliensis genome project. The findings of this thesis found that the overall prevalence of Campylobacter spp. ranged from 0-73%, although the majority of studies had a prevalence greater than 30%. The prevalence and species distribution differed depending upon the dog population. Kennelled dogs generally demonstrated the highest overall Campylobacter spp. prevalence, whilst the greatest species diversity was found in hunt dogs. C. upsaliensis dominated in most of the populations sampled, except for two hunt kennels where C. lari and C. jejuni dominated. The prevalence of C. jejuni was relatively high in some of the rescue and hunt kennels, reaching 20% and 26% respectively, whereas in vet-visiting and boarding dogs it was relatively low, 1.2-9%. Longitudinal studies indicated that the majority of dogs entered the kennels already carrying Campylobacter spp. but when possible transmission events occurred they often involved C. jejuni. Rescue dogs appeared to be exposed to sources of C. jejuni before and after entry to the kennel, but boarding dogs were only exposed after entry. The shedding of C. jejuni in dogs appeared to be over short durations, whereas dogs that carried C. upsaliensis shed the bacterium in nearly every sample. Data suggested that dogs carried the same C. upsaliensis strain throughout the study, providing further evidence that the species may act as a commensal in dogs. Further to this no associations could be made between Campylobacter spp. carriage, specifically C. upsaliensis, and disease in dogs in any of the studies. Younger dogs were significantly more likely to carry C. upsaliensis than older dogs in the vet-visiting study (OR for every additional month 0.99) and living with another dog carrying Campylobacter spp. , was significantly associated with Campylobacter spp. carriage in dogs. A considerable amount of genetic diversity was observed within the C. jejuni and C. upsaliensis isolates originating from dogs, and MLST results suggested that strains of both species were the same, or highly similar to strains found in humans. This suggests that there may be common sources of infection for both humans and dogs and that dogs remain a potential zoonotic risk to humans. Although only a small number of household dogs carry C. jejuni, infected dogs should still be considered a potential zoonotic risk to humans, particularly if the dogs originate from kennelled or hunt kennel populations where the prevalence may be higher. Dogs remain a significant reservoir of C. upsaliensis, but the relationship between the presence of C. upsaliensis and gastroenteritis in both dogs and humans is still unclear.