Dog: Ehrlichiosis

General information

Other common/scientific names: canine monocytic ehrlichiosis, Ehrlichia canis, Ehrlichia ewengii, ehrlichia

The tick population in the United States is exploding due to changing climate (less harsh winters), suburbanization and the increase in the deer population . Because of this, ticks are moving into new areas and bringing new diseases. As a result, tick-borne diseases in dogs are increasing. These diseases include anaplasmosis, babesiosis, ehrlichiosis, borreliosis (Lyme disease) and Rocky Mountain spotted fever. These diseases are typically infections of the blood. Because these infections are transmitted by a tick bite, a dog may be infected with more than one of these organisms at the same time.


Canine ehrlichiosis is caused by the bacteria Ehrlichia canis and Ehrlichia ewengii. White blood cells are part of the body’s immune system that help fight infection. Platelets are cells which promote normal blood clotting. The Ehrlichia bacteria infect and destroy the dog’s white blood cells. This results in fever, lethargy and enlarged lymph nodes. The Ehrlichia bacteria also have the ability to produce an immune-mediated disease. This results when the dog’s own immune system becomes over-reactive resulting in destruction of normal platelets. Low platelet numbers can cause abnormal bleeding. The Ehrlichia bacteria also cause formation of immune complexes which are deposited in various organs (eye, kidney, joint) causing inflammation and disease.


Dogs acquire ehrlichiosis by being bit by a tick carrying the bacteria. The brown dog tick (Rhipicephalus sanguineus) transmits Ehrlichia canis and the lone star tick (Amblyomma americanum) transmits Ehrlichia ewingii.

Abb. GSR8L5BQ: Life stages of the brown dog tick (Rhipicephalus sanguineus): Larva on the left and a nymph on the right side.
Each tick stage requires a blood meal before it can reach the next stage

Cardinal symptom



There are three phases of illness with Ehrlichiosis:

  • Acute phase: These signs occur 1 to 3 weeks after an infected tick bite and include: fever, lethargy, loss of appetite, weight loss and enlarged lymph nodes.
  • Subacute phase: In this phase, the dog appears normal. The Ehrlichia bacteria hide out in the spleen for months to years.
  • Chronic phase: In this phase, the dog appears sick again. Abnormal bleeding, pale gums and an enlarged spleen are often seen. Also seen are: uveitis (deep inflammation of the eye), chronic renal failure and arthritis due to immune-mediated disease.


Diagnosis of ehrlichiosis should be made based on the presence of clinical signs and positive blood tests. As part of your dog’s annual preventative health care, your veterinarian may recommend a four way blood test to detect heartworm infection, Lyme disease, ehrlichiosis and anaplasmosis. This test is performed in your veterinary clinic while you wait and measures antibody levels. A positive result for ehrlichiosis, however, only indicates past exposure to the bacteria not an active infection. A complete blood count may reveal low numbers of red blood cells, white blood cells and platelets. The Ehrlichia bacteria are sometimes visible on a blood sample using a microscope. Other tests can be sent to a laboratory to detect the Ehrlichia DNA in the blood.


Ehrlichiosis is treated with antibiotics. In chronic cases, when the immune system is causing clinical signs, anti-inflammatory medications may be used.


Dogs which are diagnosed and treated promptly while in the acute phase have a good prognosis for recovery. However, if left untreated, dogs with ehrlichiosis can develop chronic, debilitating symptoms.


Dogs which go outdoors in wooded, tick infested areas should have some form of tick protection such as:

Because of the warmer winters, tick protection is recommended year around.

While the topical spot-on medications are the best defense in preventing tick-borne diseases, checking your dog for ticks after walking or playing in a wooded area is recommended since it takes several hours for an attached tick to transmit disease. This is especially important if you live in a tick infested area.


When applying the topical, spot-on medications, be sure to part the hair and apply the medication directly to the skin. Do not bath or allow your dog to swim for 2 days after application. The product may need to be re-applied more often than every 30 days.

Update version: 4/24/2014, © Copyright by
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