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By Jennifer Coates, DVM

Ehrlichiosis—the term is a mouthful, but it’s worth taking the time to learn about the disease it describes. Ehrlichiosis can develop after infection with several different types of Ehrlichia bacteria. Let’s take a look at the two most common forms of the disease in dogs.

Canine Monocytic Ehrlichiosis

Canine monocytic ehrlichiosis (CME) develops after a dog has become infected with Ehrlichia canis bacteria, which are primarily transmitted to dogs through the bites of brown dog ticks (Rhipicephalus sanguineus). Brown dog ticks can be found throughout the United States (and worldwide), but are especially problematic in warmer climates, which means that ehrlichiosis is also most frequently diagnosed in these areas.

Stages of Ehrlichiosis

Dogs will appear perfectly normal for one to three weeks after being bitten by a tick carrying E. canis bacteria. If the dog is unable to fight off the infection during this time, he will enter what is known as the acute phase of infection. During this time, the bacteria are actively reproducing within a certain type of white blood cell and are spreading throughout the body. Dogs can display a variety of symptoms during the acute phase of canine monocytic ehrlichiosis, including:

  • Fever
  • Lethargy
  • Poor appetite
  • Lymph node enlargement
  • Abnormal bruising and bleeding
  • Chronic eye inflammation
  • Neurologic abnormalities
  • Occasionally lameness

These symptoms will typically last for two to four weeks if left untreated. Many dogs then appear to get better on their own and enter what is called a subclinical phase of the disease, which can last for months to years. During the subclinical phase, blood work may reveal a low platelet count (thrombocytopenia), but otherwise dogs typically appear to be perfectly normal. Some dogs never progress out of the subclinical phase of canine monocytic ehrlichiosis, but others eventually enter the chronic phase of the disease. Symptoms are similar to those described above for the acute phase, but the longer they go on, the harder they become to treat.

Canine Granulocytic Ehrlichiosis

Another type of ehrlichiosis, called canine granulocytic ehrlichiosis (CGE), is caused by infection with Ehrlichia ewingii bacteria, which are typically transmitted through the bites of lone star ticks (Amblyomma americanum). Lone star ticks are primarily found in the Eastern, Southeastern, and Midwestern parts of the United States.

The typical signs and symptoms of CGE are a little different than those that are seen with CME and include:

  • Fever
  • Lethargy
  • Lameness is common and often appears as stiffness when walking
  • Vomiting
  • Diarrhea
  • Neurologic abnormalities

What to Do If You Suspect Your Dog Has Ehrlichiosis

Whichever form of ehrlichiosis a dog has, it is important that he be evaluated by a veterinarian as quickly as possible. Diagnosing ehrlichiosis can be somewhat complicated. Many of the symptoms of ehrlichiosis are indistinguishable from those seen with other diseases like Rocky Mountain spotted fever, Lyme disease, lymphosarcoma, and certain immune disorders. As part of the diagnostic process, most veterinarians will collect a complete health history, perform a thorough physical exam, and then run a complete blood count (CBC), blood chemistry panel, urinalysis, fecal examination, and specific lab work aimed at diagnosing ehrlichiosis.

Keep in mind that the tests that are commonly used to screen for ehrlichiosis only indicate whether a dog has been exposed to Ehrlichia bacteria, and some dogs are exposed but don’t go on to become sick. Therefore, to be definitively diagnosed with ehrlichiosis, a dog should test positive for exposure, have some of the common symptoms of the disease, and respond to appropriate treatment. Other types of Ehrlichia tests are available to confirm a diagnosis of ehrlichiosis and can be used in complicated cases.

Treating Ehrlichiosis in Dogs

Veterinarians most commonly prescribe the antibiotic doxycycline to treat ehrlichiosis in dogs. It is typically given once a day for three to four weeks. Other medications can also be used when the situation warrants.

If a dog receives treatment in a timely manner, his condition will usually begin to improve rapidly, oftentimes within just a day or two, and the prognosis for complete recovery is good. In more severe cases, additional treatments (e.g., intravenous fluids, blood transfusions, immunosuppressive medications, and/or pain relievers) may also be necessary.

Preventing Ehrlichiosis in Dogs

Ehrlichiosis is a very serious disease, and dogs who have been infected once can develop it again. No vaccine is currently available to protect dogs against ehrlichiosis, although research is being done into developing one. As of now, the best way to prevent dogs from developing ehrlichiosis is to protect them from tick bites. Your veterinarian can recommend the best form of tick prevention based on your dog’s health, lifestyle, and the prevalence of ticks and ehrlichiosis in your area. 

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