Ehrlichia canis information for veterinarians

Canine ehrlichiosis is established in the Northern Territory and has been detected across northern Queensland, Western Australia and South Australia.

Any dogs that live in or travel through brown dog tick-infested areas of Australia (including the whole of Queensland) may be at risk of infection.

Assessment of suspect infections

If you suspect E. canis (the causative agent of canine ehrlichiosis) infection in a dog, it is important to seek epidemiological and clinical information about the likelihood of E. canis infection, to inform diagnostic and treatment priorities.

High-risk cases

Based on the epidemiological information provided, a likelihood assessment will inform high-risk cases. High-risk cases are dogs that meet any of the following criteria:

• living in north, north-west or far-north Queensland — Queensland local government areas previously known to be infected (as of February 2024) include Mount Isa, Cloncurry, Carpentaria, Doomadgee, Kowanyama, Burke, Mornington, Townsville, Palm Island, Mareeba and Tablelands
• a history of travel from the Northern Territory, or known infected regions of Queensland, Western Australia or South Australia
• clinical signs consistent with E. canis
• pyrexia of unknown cause and thrombocytopaenia (as priority indicators)
• unknown, inadequate or no history of tick prevention.

Cases that meet one or more of these criteria should undergo diagnostic testing as soon as possible. Early diagnosis and treatment provide the best chance of recovery.

Although the current geographical distribution of E. canis in Australia includes northern Queensland, Western Australia, South Australia and all of the Northern Territory, the disease may be present in any region where the vector (the brown dog tick Rhipicephalus sanguineus) is present.

Moving dogs into or within Queensland

Human-assisted dog movement accelerates spread of the disease and remains the highest risk for introducing E. canis to naïve tick and canine populations.

Although infection with E. canis is no longer nationally notifiable, dog owners and carers still have a general biosecurity obligation (GBO) to take all reasonable steps to prevent its spread.

Veterinarians may be asked by dog owners for advice around mitigating the risk of their dog becoming infected or preventing disease spread. Advice will vary from general advice to specific travel advice, and may include:

• undertaking a thorough veterinary clinical examination
• undertaking diagnostic testing for clinically consistent dogs
• inspecting dogs and cohorts for ticks regularly, with removal of any ticks
• maintaining the dog on an effective tick prevention and control program
• avoiding taking dogs into tick-infested areas (e.g. the bush)
• for dogs travelling from known infected areas, undertaking a complete blood count and/or diagnostic testing (with negative results) before travelling, as well as
  • observation that the dog is, and remains, clinically healthy between the time of testing and travel
  • isolating dogs from other dogs and tick vectors at the start of a testing regime.

Diagnosis

E. canis can be detected by:

• real-time polymerase chain reaction (PCR) test
• serological tests
  • enzyme-linked immunosorbent assay (ELISA)
  • indirect fluorescent antibody test (IFAT).

ELISA and PCR tests are conducted at our Biosecurity Sciences Laboratory.

Where to submit samples

You can submit samples for E. canis PCR and/or ELISA testing directly to our Biosecurity Sciences Laboratory. E. canis testing of samples from all dogs or ticks (for any reason) will incur laboratory fees — wider diagnostic testing will not be completed.

Samples requiring comprehensive diagnostic testing should be submitted to your preferred commercial veterinary laboratory. They may refer samples to the Biosecurity Sciences Laboratory for exclusion of E. canis infection.

Types of samples to submit

Live or recently deceased/euthanased animals

Blood samples to take from live or recently deceased/euthanased animals:

• PCR testing: 2–5ml blood in an EDTA tube (purple top)
• serological testing: 2–5ml in a plain tube (red or grey/red speckled top) — if possible, 1–2ml aliquot of clear serum should be obtained.

Dead animals

Blood or tissue samples to take from dead animals:

• unclotted heart blood (if available)
• fresh samples of lung, spleen, liver, kidney and submandibular lymph node in separate screw-top containers, and a range of formalin-fixed tissues.

Ticks

You can send ticks to the Biosecurity Sciences Laboratory for identification and PCR testing. Ticks can be collected from the affected dog and placed in 70% ethanol or 40% propylene glycol.

Ethanol:

• if transporting by road, ticks may be submitted in 5ml tubes with 2.5ml of 70% ethanol along with other diagnostic samples
• cannot be transported by air or through Australia Post.

Laboratory diagnosis

Application of the following diagnostic interpretation matrix to the PCR and ELISA results will assist in determining a dog's infection status.

*Negative PCR and ELISA results may occur in animals very early in infection or may indicate a subclinical carrier state. In high-risk cases or those with an unknown history, resampling and retesting at least 14 days later may be recommended.

Other laboratory abnormalities associated with E. canis, more commonly in chronic infections, may include:

• thrombocytopaenia (moderate to severe)
• leucocytosis (acute) or leucopaenia (chronic)
• anaemia (mild to severe)
• pancytopaenia (chronic)
• hyperglobulinaemia
• hypoalbuminaemia
• elevations in liver enzymes (mild)
• azotaemia (mild to moderate).

Control

Prevention

Most dogs can be protected from ehrlichiosis by using an effective tick prevention and control program, that includes topically-applied acaracides that repel and kill on contact.

Although systemically-acting products (tablets or chewables) are highly effective in killing the brown dog tick and helpful in reducing the rate of community transmission, these products do not prevent transmission of E. canis to dogs.

It is important to keep in mind that no product offers 100% efficacy against ticks. Therefore, 100% protection from ehrlichiosis cannot be guaranteed, particularly where collar retention or spot-on application is not continuously maintained.

Treatment

To prevent onward transmission, dogs known or suspected to be infected with E. canis should immediately be treated with a registered acaracide. Topically-acting products that repel and kill are recommended. Treatment of the dog's home environment should also be advised.

Doxycycline at 10mg/kg PO SID (or 5mg/kg BID) for 28 days is the recommended treatment for both acute and chronic ehrlichiosis.

Consider supportive treatments and management of immune complex pathology or comorbidities, as appropriate.

The stage of infection is not always clear, but cases treated later in the course of disease carry a poorer prognosis. Chronic ehrlichiosis carries a grave prognosis, regardless of treatment intervention and effort.

Also consider

• Read the Canine monocytic ehrlichiosis - A guide for veterinarians (PDF, 1.73MB).
• Read the Ehrlichiosis: additional veterinary guidelines for managing CME in Australia (PDF, 250KB).
• Read the canine ehrlichiosis disease overview.