Canine ehrlichiosis is caused by the bacteria Ehrlichia canis, which is transmitted by Rhipicephalus sanguineous, commonly known as the brown dog tick. As its name suggests, the tick prefers to dine on dogs; other animals, including humans, are far less prone to infection.  The infection is spread by an infected tick and thus we class it as a vector borne disease; it doesn’t pass directly from dog to dog. It falls into a category of diseases known as arthropod – borne disease. Other examples of human diseases in this category are:

• Lymes Disease (bacteria)
• Rocky Mountain spotted fever  (bacteria)
• Ross River Virus (virus)
• Dengue Fever (virus)
• Malaria (not bacterial or viral – parasitic cell)

Zoonotic (Can it infect humans)

Little is known about the zoonotic potential of E. canis, though one study(link) in 2006 found that it had sickened a handful of people in Venezuela. Experimentally infected Rhesus monkeys exhibited severe signs of infection.

In Dogs

The infection usually has three phases: acute, subclinical and chronic.

Acute Phase

Clinical signs  arise one to three weeks following the bite of an infected tick, and may include :

• listlessness,
• loss of appetite,
• enlarged lymph nodes ( thse are your immune system glands)
• fever

If treated during the acute phase most dogs recover, but if untreated or inadequately treated, they may enter a subclinical phase in which they appear normal.

Subclinical phase

This phase can last months or even years the bacteria hides away in the spleen.

Chronic Phase

Dogs may not ever progress to the chronic phase. However, if they become sick again – signs include:

• severe fever
• inflammation in the eyes
• abnormal bleeding
• • including from lesions on the skin
    and mucosa
  • and nose bleeds.

Diagnosis

Diagnosis is made by detecting genetic material of the bacteria (with a polymerase chain reaction, or PCR, test) or by detecting antibodies in the patient’s blood (through serology).   We can take a sample for testing here at the clinic and have access to a wide range of laboratories offering different testing options for our pets.

How far has ehrlichiosis spread – should we be worried?

A veterinarian, located in the far north of Western Australia, initially detected the disease. They noted clinical signs in a few dogs that were not consistent with common diseases. A pathology lab received samples and the bacteria was identified during pathological screening.  Once that had occurred more cases were identified in the Northern Territory.   Last month a case was identified in South Australia and New South Wales has identified several dogs as well.    There were dogs moved from the Northern Territory into Queensland prior to diagnosis.  The disease has thus been recorded in 5 States or Territories of Australia.    It should be expected to spread to any area that the Brown Dog Tick is endemically embedded.

Is Ehrlichiosis likely to Spread further?

E. canis had been endemic in parts of every continent except Australia for the past 80 years. The pathogen was first identified in the 1930s by French scientists in Algeria. Coming to prominence in the 1960s and 1970s after it killed scores of American military dogs serving in the Vietnam War.

The brown dog tick, preferring warmer climates, is more likely to flourish in tropical and subtropical regions. However Irwin thinks it’s only a matter of time before canine ehrlichiosis becomes more widespread in Australia. Australia has quite a varied climate but the adaptability of the tick leave the potential for the disease to crop up in big cities such as Sydney, Brisbane and Perth, where brown dog ticks are present in small numbers. 

Over the longer term, climate change is likely to play a role expanding the ticks’ preferred habitat. Increasingly warm environments will expand the range of the vector, the Brown Dog tick.

The biggest factor that will slow the spread is the use of preventatives.    There are communities in Queensland where there is a low socioeconomic index combined with high unemployment lead to a very low compliance with any sort of tick control.  Many of the dogs will carry ticks year round.   The nature of the disease having a very long sub clinicial period means theses animals are the perfect vector.

How did this happen?

Australia’s Bio-security has been considered somewhat of a fortress comparatively to other countries, with many relying on our excellent record and using us as a check point for themselves. e.g. Vanuatu and other pacific islands.   If we cannot identify to entry point then we may not be able to maintain our disease free status for other canine diseases.  There are theories, none of which currently have any solid evidence.   This leads to the 2nd important but related reason best voiced by Dr Irwin:

Hopefully with genetic analysis we can at least identify the potential source and look to better control that entry point.