Ehrlichia canis has been suspected to exist clinically in northern Australia, but its presence has yet to be confirmed. Ehrlichia canis infects monocytes and causes canine monocytic ehrlichiosis (CME). Apparently the host and environmental conditions are favourable for its occurrence in northern Australia but at present it is regarded as a potential exotic disease. It is endemic in South East Asia and is transmitted by the common brown dog tick (Rhipicephalus sanguineus). Stringent quarantine regulations are enforced to prevent its entry into Australia. Dogs living in most countries must be tested, prior to importation, for E canis antibodies using an indirect fluorescent antibody test (IFAT) performed at the Australian Animal Health Laboratory, Geelong. Dogs must be serologically non-reactive to permit entry into this country. E ewingii by contrast, infects granulocytes (neutrophils and, less commonly, eosinophils) causing canine granulocytic ehrlichiosis (CGE) (Irwin PJ, 2001). 

In endemic regions of the United States, Borrelia organisms are ubiquitous in the tick population, exposure of dogs and cats to infected ticks extensive, and many seropositive dogs remain asymptomatic, despite demonstration of spirochaetaemia. In contrast to human Lyme borreliosis, Ig-M titres to Borrelia burgdorferi remain positive for several months in asymptomatic dogs, and antibody titres fail to decrease following appropriate antibiotic treatment in symptomatic dogs. Immunoblot analysis of the Ig-G response to Borrelia burgdorferi indicates that naturally exposed dogs from different geographic regions exposure to similar organisms, and there is no difference in the immunoblot pattern between asymptomatic and symptomatic dogs with high Borrelia burgdorferi antibody titres. Thus serological support for a pathogenic role in cats and dogs is still lacking. Although the varied case reports of canine Lyme borreliosis are convincing, two of Koch's postulates are not satisfied, ie induction of disease in a susceptible dog with the cultured organisms and re-isolation of the organisms from the experimentally infected animal. Much of the recent literature is derived solely from serological diagnosis of Lyme borreliosis in dogs and cats from endemic regions where seroprevalence approximates 80%. Because seropositivity rather than seroconversion has been used as a criterion for diagnosis, the relevance of these case reports to the clinical spectrum of canine and feline Lyme borreliosis remains highly suspect (Hoskins JD, 1991).