Canine ehrlichiosis

The bacteria Ehrlichia canis

E. canis is found in most of the world and follows the distribution of the vector, the brown dog tick Rhipicephalus sanguineus.

In May 2020, it was confirmed in domesticated dogs in the Kimberley region of Western Australia. This was the first detection of E. canis in Australia.

Further detections have occurred in the Pilbara, Gascoyne and northern Goldfields regions of Western Australia. E. canis has also been confirmed in Port Augusta and northern South Australia, and ehrlichiosis is considered established throughout the Northern Territory.

A Queensland dog tested positive for the disease in July 2021 after travelling through Western Australia and the Northern Territory. In early 2022, a case was confirmed in northwest Queensland in a dog that was reported to not have travelled outside the state. There continues to be ongoing detections of E. canis in Queensland dogs residing within the local government areas of Mount Isa, Doomadgee, Cloncurry and Carpentaria, and in dogs having travelled through these areas and infected areas interstate. The detection of E. canis in Townsville in December 2022, and in Mornington Island, Palm Island and Mareeba in 2023, demonstrates the disease may be widespread in northwest, north and far north Queensland.

Human-assisted movement of dogs is considered the most likely means of spreading E. canis in Queensland.

Domesticated or wild animals in the family Canidae including dogs and foxes are considered to be the reservoir hosts.

Infected ticks, primarily the brown dog tick (Rhipicephalus sanguineus), are vectors for E. canis infection between dogs.

E. canis is maintained in cycles between ticks and either domesticated or wild animals in the family Canidae, including dogs and foxes.

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. Adults may then produce eggs which are not infected with E. canis.

Dogs do not transmit the disease to each other, however, the organism can be transmitted directly from dog to dog through blood transfusions.

Disease phases

Canine ehrlichiosis has 3 disease phases:

• acute
• subclinical
• chronic.

The severity of clinical signs can vary considerably among dogs.

The incubation period for the development of acute disease is about 1–3 weeks although the chronic form may not show any clinical signs until months or years after infection.

Acute phase

This phase is characterised by non-specific clinical signs, including:

• fever
• lethargy
• enlarged lymph nodes
• anorexia
• weight loss
• discharge from the nose and eyes
• bleeding disorders such as nosebleeds or bleeding under the skin that looks like small spots, patches or bruising.

There are usually abnormalities on blood tests including low platelets and mild anaemia. This phase typically lasts for 2–4 weeks.

In countries where ehrlichiosis is established and endemic, death is rare during this phase. Most dogs recover after 1–2 weeks without treatment however some may remain persistent subclinical carriers for months or years.

However, in Australia, where the disease is infecting a naïve population, very high morbidity with severe illness and mortality occur in the acute phase.

Subclinical phase

As noted above, some dogs may progress from the acute phase and become subclinical carriers for months or years. These dogs present no clinical signs and therefore may not seem to require veterinary attention.

Subclinical dogs either:

• clear (get rid of) the organism
• remain asymptomatically infected
• progress to the chronic form of ehrlichiosis

The likelihood that subclinically infected dogs will go on to develop chronic, end-stage ehrlichiosis is unknown.

Chronic phase

Clinical signs are similar to the acute phase but are more severe. They can include:

• fever
• weakness
• weight loss
• bleeding disorders
• pale mucous membranes
• eye abnormalities
• neurological abnormalities.

Infected dogs may be more susceptible to secondary infections. Blood tests often show severely low platelets, low white blood cells and anaemia. This form of the disease is usually fatal and treatment efforts are likely to be futile.

Transmission between dogs and other canids

Transmission between canids requires the tick vector. Transmission of E. canis from infected ticks to uninfected canids can occur within a few hours of attachment. Canids may also become infected 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.

Transmission to humans

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 tick.

Diagnosis

Ehrlichiosis is diagnosed through a combination of:

• consistent clinical signs
• blood tests.

If you see clinical signs consistent with ehrlichiosis, you should consult your private veterinarian and seek assessment as soon as possible. Early diagnosis and treatment provide the best chance of recovery.

Veterinarians can contact Biosecurity Queensland for advice on submitting samples or refer to the information for veterinarians on Ehrlichia canis information.

Surveillance

Areas where the brown dog tick exists may pose a risk of ehrlichiosis to dogs. Surveillance to determine the distribution of the brown dog tick and E. canis is continuing to help refine the area where E. canis is known to be active. The current areas where E. canis is known to be active are:

• the entire Northern Territory
• the Kimberley, Pilbara, Gascoyne, and northern Goldfields regions of Western Australia
• Port Augusta and northern South Australia
• northwest Queensland, particularly the local government areas of Mount Isa, Cloncurry, Carpentaria, Doomadgee, Mornington and Kowanyama
• Townsville, Palm Island and Mareeba.

Movements of dogs from these areas must be managed.

Movement conditions and obligations of dog owners

As a dog owner in Queensland, you have a general biosecurity obligation to be aware of and manage the risk of E. canis infection.

You should maintain your dog on an effective tick prevention and control program, avoid taking your dog into tick-infested areas as much as possible and regularly inspect your dog for ticks.

Even if you are taking these steps, if you are moving your dog from an area where E. canis is known or likely to be active you should assess your dog’s health before entering or moving within Queensland. If your dog has not been on a tick prevention program, is unwell, or you are unsure, seek veterinary advice.

People moving or bringing dogs from interstate or adopting rescue dogs should always ask questions about where the animals came from, their history, their health status and what tick prevention they have prior to bringing them to Queensland or moving them within Queensland.

Veterinary examination and testing of dogs prior to movement will help ensure only uninfected and healthy dogs are moved and E. canis is not introduced or unknowingly spread within Queensland.

Dog owners are requested to remain diligent in managing the risk of E. canis and remain vigilant to the signs of disease. If you suspect the presence of this disease in any dog seek veterinary advice. You or your veterinarian must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Animal Disease Hotline on 1800 675 888.

Prevention

There is no vaccine for ehrlichiosis. To help protect your dog from infection:

• maintain an effective tick prevention and control program. An effective tick prevention and control program will include:
  • using an external tick control that kills ticks on contact. Products that allow the tick to feed before killing the tick do not prevent infection.
  • treatment of bedding, kennels and yards to prevent reinfection from the environment.
• avoid taking dogs into areas where E. canis is known or likely to be active
• avoid taking dogs into tick-infested areas, such as the bush, as much as possible
• inspect dogs for ticks after being in areas where E. canis is known or likely to be active or in tick-infested areas and carefully remove any ticks.

Veterinarians can provide advice on tick prevention and control programs, effective products and tick removal.

Treatment

In addition to removal of ticks and applying an appropriate tick control program, E. canis infection in dogs may be treated by a veterinarian with antibiotics. In some cases, supportive therapy and hospitalisation may be necessary. Early treatment provides the best chance of recovery.