Monocytic ehrlichiosis

What is it?

It is a disease caused by Ehrlichia canis, an organism transmitted by the "brown dog tick" (Rhipicephalus sanguineus), and that infects certain white blood cells in dogs, such as monocytes, marcophages, and lymphocytes. 

The organism is found worldwide in all of the tropical and subtropical regions. 


The disease presents itself in three phases: acute, subclinical, and chronic. 

During the acute phase, which occurs between 1 to 3 weeks following inoculation, and lasts up to 2 to 4 weeks, we generally observe: 

  • fever;
  • depression;
  • loss of appetite;
  • weight loss;
  • enlarged spleen and lymph nodes; 
  • nasal and ocular discharges (rare);
  • petechiae (minor bleeding caused by an absence of platelets) and hemorrhagin (rare);
  • neurological signs (rare).

The resolution of the acute symptoms is often spontaneous. 

During the suclinical phase, which occurs 4 to 5 weeks after the acute phase and lasts for several months to years, there are no symptoms present, if there is nothing but a decrease in the platelet number and increase in the number of antibodies. 

The chronic phase occurs several weeks to months after the infection. The following symptoms are often evident: 

  • lethargy;
  • loss of appetite;
  • weight loss;
  • petechiae and bleeding (20%-60% of cases);
  • increase in the size of lymph nodes and spleen (less frequent);
  • uveitis and neurological anomalies (occasional); 
  • kidney inflammation, hyperviscosity of the blood, and lameness (rare).

The organism cycle

When an infected tick ingests a dog's blood, it transmits the organism which multiplies in their white blood cells and  tissues (spleen, liver, and lymph nodes). 

The infected cells then attach to the linings of the blood vessels, lungs, kidneys, joints, and meninges, and causes damage. 

Eventually, problems associated to coagulation and generalized inflammation will appear, as well as involvement of the bone marrow. 

Is the organism contagious to humans?

Humans can be infected by this organism, but not through dogs. 

The diagnosis

There many tests that exist to diagnose the infection. Some are specific and used to highlight evidence of the organism, whereas others are routine and allow to identify the presence of "collateral damage" caused by the microorganism.

Specific tests include: 

  • serological tests to quantify the number of antibodies against the organism. The test should be repeated two to four weeks later to confirm infection; the number of antibodies should increase;
  • DNA testing.

The routine tests include bood tests and other complementary tests. 

Blood tests often reveal the following changes: 

  • A decrease in blood platelets typically occurs;
  • Decrease in the number of neutrophils; 
  • Anemia; 
  • An increase in the number of lymphocytes, monocytes, and eosinophils; all of the white blood cells; 
  • An increase in the number of antibodies;
  • A possible loss in proteins in the kidneys

Among the additional tests, we have: 

  • Examination of the fundus of the eye. We can sometimes observe a hemorrhage and/or detachment of the retina; 
  • Abdominal xrays. The spleen can be visibly larger; 
  • Puncture of the lymph nodes when they are enlarged; 
  • X-rays of the limbs and sampling of the joint fluid if inflammation is present' 
  • X-rays of the limbs with joint fluid aspiration if the joints are swollen;
  • Bone marrow puncture if a decrease in the number of platelets is noted on the blood test; 
  • Sampling of cerebrospinal fluid when there are neurological symptoms present.  


Antibiotics are used during the acute phase of the disease to eliminate the organism. 

Supportive treatment is added as needed, such as blood transfusions if the anemia is severe, and analgesics if pain is felt, etc. 

It is possible that additionnal antibiotics are given during the chronic phase if bacterial resistance is indicated. 


The animal usually demonstrates a rapid improvement when treatments are established during the acute phase or when the symptoms asscoiated to the chronic phase of the disease are weaker. 

However, the prognosis is from reserved to poor when there is a significant decrease in white blood cells accompanied with hemorrhaging complications or concomitant infections. 


The best way of preventing the infection is by having access to proper tick control.

Different types of medications, sold under prescription, exist which are safe and effective in preventing tick infestations. 

Do not hesitate to ask one of our staff members for advice on which product best suits your pet.