Ehrlichia canis – A guide for veterinarians Version: 1.1 Contents 1 Purpose ...................................................................................................................................... 2 2 Nationally notifiable disease ....................................................................................................... 2 3 Background and context ............................................................................................................. 2 4 Warning ...................................................................................................................................... 2 4.1 Zoonosis ................................................................................................................................... 2 5 Nature of the disease ................................................................................................................. 2 5.1 Aetiology .................................................................................................................................. 2 5.2 Susceptible species ................................................................................................................. 3 5.3 Epidemiology............................................................................................................................ 3 5.3.1 Incubation period ................................................................................................................. 3 5.3.2 Lifecycle ............................................................................................................................... 3 5.3.3 Factors influencing transmission ......................................................................................... 3 5.4 Diagnostic criteria .................................................................................................................... 4 5.4.1 Clinical signs ........................................................................................................................ 4 5.4.2 Differential diagnoses .......................................................................................................... 5 5.5 Laboratory tests ....................................................................................................................... 5 5.5.1 Preferred samples ................................................................................................................ 5 5.5.2 Laboratory diagnosis ............................................................................................................ 5 6 Prevention ................................................................................................................................... 6 7 Treatment ................................................................................................................................... 6 8 Control of confirmed infected dogs ............................................................................................. 6 9 Movement controls ..................................................................................................................... 6 1 Purpose These guidelines are specifically intended to assist veterinarians in the investigation of illness in dogs where infection with Ehrlichia canis (erhichiosis) is considered a possible cause. Investigation of possible E canis infection is a joint approach between dog owners, private veterinary practitioners and Biosecurity Queensland. Biosecurity Queensland will coordinate a response to confirmed or suspected reports of E canis infection. Private veterinary practitioners will be integral in the field-level epidemiological investigation, collection and submission of diagnostic samples, and communication with dog owners. Dog owners need to be aware of and manage risks associated with E. canis infections in dogs under the general biosecurity obligation described in the Biosecurity Act 2014. 2 Nationally notifiable disease E. canis infection is nationally notifiable. In Queensland, it is neither restricted nor prohibited matter under the Biosecurity Act 2014 though it could pose a biosecurity risk (i.e. could cause an adverse effect on a biosecurity consideration) to other animals and the environment. 3 Background and context Canine ehrlichiosis is a tick-borne disease of dogs caused by infection with the bacteria Ehrlichia canis. Dogs become infected with E. canis after being bitten by an infected tick, primarily the brown dog tick (Rhipicephalus sanguineus). Ehrlichiosis is an intracellular bacterial infection that primarily infects the cells of the immune system. Infected dogs can present with a range of clinical signs. E. canis occurs worldwide, particularly in tropical and subtropical regions. It was confirmed in domesticated dogs in the Halls Creek and Kununurra area of Western Australia in May 2020. This was the first detection of E canis in Australia. Further detections have occurred in the Pilbara region of Western Australia. It was subsequently confirmed in domesticated dogs in Katherine and in a remote community west of Alice Springs in the Northern Territory in June 2020. The current geographical distribution of E. canis in the Australian canid population is unknown. Delimiting surveillance and tracing following the detections in Western Australia and Northern Territory will inform the distribution of the disease and the tick vector. E. canis has not been detected in Queensland. 4 Warning 4.1 Zoonosis Infected canids do not transmit E. canis to people. In rare cases, people may become infected with E. canis after being bitten by an infected brown dog tick (Rhipicephalus sanguineus). 5 Nature of the disease 5.1 Aetiology The causative agent of ehrlichiosis is the intracellular bacteria Ehrlichia canis. Ehrlichia canis – A guide for veterinarians, Department of Agriculture and Fisheries, 2020 2 E. canis infections in dogs may be referred to as: • canine monocytic ehrlichiosis • canine tropical pancytopenia • tracker dog disease • canine haemorrhagic fever • canine typhus. 5.2 Susceptible species Domesticated or wild animals in the family Canidae including dogs and foxes are susceptible to E. canis infections. It is plausible that the dingo is a suitable host for R. sanguineus and is susceptible to infection by E. canis. The pathogenicity and virulence of an E. canis infection in dingoes is not known but is likely to be similar to disease seen in domestic dogs or other canids. Infected ticks, primarily the brown dog tick, are vectors for E. canis infection between dogs. Several published reports suggest cats may also become infected, though the natural transmission pathway has not been established and infection is considered uncommon. Infected dogs do not transmit E. canis to people. In rare cases, people may become infected with E. canis after being bitten by an infected brown dog tick. 5.3 Epidemiology 5.3.1 Incubation period The incubation period for the development of acute disease in dogs is about 1-3 weeks although the chronic form may not show any clinical signs until months or years after infection. 5.3.2 Lifecycle E. canis is maintained in cycles between brown dog tick and either domesticated or wild animals in the family Canidae. Ticks acquire E. canis by feeding, as larvae, on infected canids. Once infected, the larvae maintain their infection and may transmit the infection to other canids when feeding as nymphs or adults. The brown dog tick is a three-host tick, therefore any larvae feeding on an infected animal has the potential to infect two additional animals (as a nymph or adult) as part of the tick’s life cycle. Adult females produce eggs which are not infected with E. canis. 5.3.3 Factors influencing transmission Dogs do not transmit the disease to each other, however the organism can be transmitted directly from dog to dog through blood transfusions. As E. canis is not naturally directly transmissible between dogs, possible pathways for its spread include movement of: • actively infected vectors that may infect naïve dogs (dogs that haven’t been exposed to the bacteria before) in new locations • acutely infected dogs that infect naïve tick populations in new locations • chronically infected dogs that infect naïve tick populations in new locations. Ehrlichia canis – A guide for veterinarians, Department of Agriculture and Fisheries, 2020 3 5.4 Diagnostic criteria 5.4.1 Clinical signs Canine ehrlichiosis has three disease phases: • acute • subclinical • chronic. The severity of clinical signs can vary considerably among dogs. 5.4.1.1 Acute phase This phase is characterised by non-specific signs, including: • pyrexia • lethargy • lymphadenopathy • anorexia • weight loss • ocular and nasal discharges • bleeding tendencies including petechiae, ecchymoses and epistaxis. Thrombocytopaenia is a common finding. This phase typically lasts for 2-4 weeks. 5.4.1.2 Subclinical phase Some dogs that recover from the acute phase can become subclinically infected. There is also a subset of dogs that show mild or no early clinical signs but are subclinically infected. This phase can persist for months to years. A mild thrombocytopenia may be present in the absence of clinical signs. Subclinical dogs either: • clear the organism • remain asymptomatically infected • progress to the chronic form of ehrlichiosis. 5.4.1.3 Chronic phase Only some dogs will develop chronic ehrlichiosis. Clinical signs are similar to the acute phase but are more severe. They can include: • pyrexia • weakness •