Canine tick-borne pathogens and associated risk factors in dogs presenting with and without clinical signs consistent with tick-borne diseases in northern Australia.

OBJECTIVES: To estimate the proportion of canine tick-borne disease (CTBD) pathogens in dogs from northern states of Australia presenting with and without clinical signs/laboratory abnormalities suggestive of CTBD and to evaluate associated risk factors.
DESIGN: Client-owned dogs presented to a general practice clinic in the Northern Territory (NT; n = 138) and five referral hospitals in south-east Queensland (SEQ; n = 100) were grouped into CTBD-suspect and -control groups based on clinical and laboratory criteria. Blood and sera were screened for haemotropic Mycoplasma spp., Babesia spp., Anaplasma spp., Ehrlichia spp. and Hepatozoon spp. using microscopic examination, in-clinic ELISA testing and PCR assays. Dog-specific risk factors associated with the presence of CTBD pathogens were evaluated.
RESULTS: Overall, 24.4% of the suspect group and 12.2% of the control group dogs were infected. The proportions of M. haemocanis, B. vogeli, A. platys, Candidatus Mycoplasma haematoparvum, and C. Mycoplasma haemobos were 7.1%, 5.0%, 3.8%, 1.7% and 0.4%, respectively. Dogs originating from the NT were 3.6-fold (95% confidence interval (CI) 1.51-8.62; P = 0.004) more likely to be infected with CTBD pathogens than those from SEQ. Male dogs were 2.3-fold (95% CI 1.17-4.80, P = 0.024) more likely to be PCR-positive to CTBD pathogens than female dogs. Dogs presenting with clinical signs consistent with CTBD and thrombocytopenia were more likely to be infected by CTBD pathogens (odds ratio 2.85; 95% CI 1.16, 7.02; P = 0.019).
CONCLUSIONS: Haemotropic mycoplasmas were the most common tick-borne pathogen infecting client-owned dogs. Subclinical cases were common in dogs from the NT. Veterinary practitioners should be aware of the proportion of CTBD pathogens and the presenting features of clinical and subclinical disease in their area.