Canine vector-borne diseases (CVBD) represent a growing challenge facing practicing veterinarians in Australia. Limited reports of CVBD prevalence, low index of suspicion for CVBD and poor availability of sensitive PCR-based diagnostic assays locally may lead to incorrect diagnosis and treatment of the animal. The emergence of parasitic and zoonotic diseases due to global warming, an increase in pet travel and expansion of disease vectors are likely to have considerably influenced the distribution of CVBD agents in this country.
Therefore, there is a need to conduct research studies in order to overcome knowledge gaps with respect to CVBD. This study aims to investigate the prevalence of CVBD pathogens using different diagnostic assays in different groups of dogs, namely pound dogs, Indigenous community dogs and client-owned dogs from southeast Queensland (SE QLD) and the Northern Territory (NT). These CVBD are namely canine babesiosis, anaplasmosis, ehrlichiosis, haemotropic mycoplasmosis, hepatozoonosis and rickettsiosis.
This study represents the first canine tick-borne (CTB) prevalence study to examine haemotropic mycoplasmas and Hepatozoon spp in Australia. It also is the first to phylogenetically characterise the haemotropic mycoplasmas in Australia. In this study, 49.2% and 3.0% of Indigenous community dogs from the NT and pound dogs from SE QLD, respectively were infected with at least one CTB pathogen. Five species of CTB pathogens were detected molecularly in dogs from Indigenous communities and pounds in SE QLD. Overall, 36.2% of Indigenous community dogs were infected with A. platys, 17.7% with Mycoplasma haemocanis, 10% with B. vogeli and 2.3% with Candidatus Mycoplasma haematoparvum. Co-infection was detected in 16.9% of dogs. With respect to pound dogs, 2% were infected with A. platys and 1% with Candidatus Mycoplasma haemobos. Younger aged dogs within the Indigenous community were found e more likely to be infected with B. vogeli. For Canine SNAP® 4Dx assay, none of the pound dogs were seropositive to Anaplasma spp. None of the dogs (including client-owned dogs) examined in this study were infected by Ehrlichia spp. and Hepatozoon spp.
Overall, 16.4% of client-owned dogs (24.4% of the suspect dogs and 12.2% of control dogs) from the NT and SE QLD were infected by at least one pathogen. The most common CTB pathogens infecting dogs were Mhc (7.1%), followed by B. vogeli (5.0%), A. platys (3.8%), CMhp (1.7%) and CMhb (0.4%). The occurrence of CTB infection was significantly higher (Odds ratio: 3.6; 95% CI: 1.51, 8.62; P = 0.004) in dogs from the NT compared to those from SE QLD. This finding was attributed to the tropical climate in the NT which favours the vector, R. sanguineus. Male dogs were 2.3 times (95% CI: 1.17, 4.80; P = 0.024) more likely to be infected with CTB infection than female dogs which could be attributed to their behaviour or preference of staying outdoor, which would likely increase their susceptibility. Dogs presented with clinical signs and thrombocytopaenia were 2.9 times (95% CI: 1.16, 7.02; P = 0.019) more likely to be infected compared to dogs not showing similar signs or haematological abnormalities. This study showed the superiority of PCR-based tests for diagnosis of CTB infection over serological test and microscopic examination.
The present study also made the first report of R. felis infection in dogs in Australia, and describes the first cluster of canine rickettsaemia caused by this agent in the world. Rickettsia felis is an emerging zoonosis causing flea-borne spotted fever or cat flea typhus in humans. The pathogen has also been successfully isolated for the first time in Australia by cell culture from infected cat fleas. This enabled the production of antigen for serological testing for future seroprevalence studies or diagnostic applications. To date, a mammalian reservoir for R. felis has not been identified. Nine percent of pound dogs and 2.3% of Indigenous community dogs were found to carry R. felis DNA. The molecular evidence of R. felis infection in dogs showed that dogs may have the potential to act as vertebrate reservoirs and sentinel hosts for human infection.
Microimmunofluorescence testing has been employed to detect antibodies against R. felis in dogs in the NT and SE QLD. The results showed 50.7% of dogs showed seropositivity with titres ≥ 64 and 18.5% with titres ≥ 128. At titres ≥ 64, dogs with active ectoparasite control were less likely (OR: 2.6; 95% CI: 1.20, 5.56) to be exposed to R. felis. The finding demonstrated the ubiquitous exposure of dogs to R. felis and the importance of ectoparasite control in preventing the exposure to the agent. It should raise awareness in veterinary practitioners and public health authorities concerning the presence of the R. felis infection in these regions.
The infection rate of R. felis in fleas collected from dogs in SE QLD was determined for the first time in this region. This study showed that 51.6% of cat fleas pools captured from dogs in SE QLD were harbouring the pathogen. This result provides strong evidence of the existence of a peridomestic cycle for this pathogen in Australia.
In conclusion, the findings of this work indicate that veterinarians should be aware of the existence of CVBD pathogens and consider them in the differential diagnosis of dogs showing CVBD clinical signs and/or laboratory abnormalities. In particular, owners should be advised of the public health implications of R. felis, and the importance of ectoparasite control in prevention of zoonotic infection.