Ticks can cause a host of illnesses, including ehrlichiosis, which affects dogs and people alike. A bite from an infected tick can mean tiredness, fever, and swollen lymph nodes upon infection. Symptoms may vanish but reappear weeks or years later. An infection that has progressed can cause bleeding, anemia, seizures, and autoimmune disease. Fortunately, antibiotics can treat ehrlichiosis. There is no vaccine against the disease; avoiding ticks is the best bet.


Ehrlichiosis is a disease caused by bacteria of the Ehrlichia family. Several species of the Ehrlichia bacteria are known to exist, some of which can infect humans. Ehrlichiosis (whether it occurs in dogs or humans) is transmitted through the bite of a tick, most typically the brown dog tick. 

After the Ehrlichia organism enters the body through a tick bite, it affects the cells in the dog’s bloodstream. White blood cells (needed to fight infection), red blood cells (needed for carrying oxygen throughout the body), and platelets (needed to help form blood clots) can all be affected.

It’s important to note that though both humans and dogs can be infected, neither dog-dog or dog-human transmission is known to exist. A tick itself is always the culprit.

Symptoms and Identification

Ehrlichiosis causes three distinct clinical phases of illness: acute, subclinical, and chronic.

In the acute phase, clinical signs occur about one to three weeks after an infected tick bites a dog. Symptoms associated with this phase can include lethargy (tiredness), fever, appetite loss, and enlarged lymph nodes. In some cases, clinical signs can resolve without treatment. However, if the infection is not treated, it progresses to the subclinical phase.

In the subclinical phase, the dog may appear completely normal because clinical signs are not observed. This phase may last many months or even years, but eventually the bacteria can reactivate and start to cause illness again.

In the chronic phase, the dog may again show vague signs such as fever, lethargy, and appetite loss. However, as the Ehrlichia organism affects the blood cells and bone marrow, clinical signs may include bleeding problems and anemia (an inadequate number of red blood cells). At this point, the bacteria may also affect the brain, causing seizures and poor coordination.

Other clinical signs associated with ehrlichiosis can include joint pain and swelling as well as autoimmune disease in which the dog produces antibodies that damage its own cells. If ehrlichiosis causes severe complications, death can result.

Clinical signs of ehrlichiosis can resemble those of other tick-borne diseases, such as Lyme disease and Rocky Mountain spotted fever. Additionally, dogs can be infected with ehrlichiosis and other tick-borne diseases at the same time, which is why veterinarians tend to recommend screening for other tick-borne diseases during the diagnostic testing for ehrlichiosis.

In fact, any time a patient’s medical history includes tick exposure and suspicious clinical signs, tick-borne disease testing is strongly recommended. A CBC (complete blood cell count) may also show changes in white blood cells, red blood cells, or platelets that may increase suspicion. However, not all dogs develop these changes, so a CBC can have normal results even if a dog is infected with Ehrilichia.

Many veterinarians diagnose ehrlichiosis using a SNAP test either when they suspect the disease or as a simple annual screening. SNAP tests are a group of quick, convenient, blood tests that can be performed at your veterinarian’s office. The available SNAP tests include:

  • The SNAP Heartworm RT Test screens for heartworm infection.
  • The SNAP 3Dx Test simultaneously screens for heartworm disease, Lyme disease, and ehrlichiosis.
  • The SNAP 4Dx Test can diagnose four diseases at the same time: heartworm disease, Lyme disease, ehrlichiosis, and anaplasmosis (which is another disease that is transmitted to dogs through a tick bite).

In some cases, veterinarians will recommend additional testing to follow up a SNAP test result or to look for other evidence of illness related to heartworm disease or one of the tick-borne infections. This testing may involve sending additional blood samples to a laboratory for further analysis or performing other diagnostic tests to gain more information about a patient’s condition.

Affected Breeds

No breed predilection has been established for ehrlichiosis infection in dogs.


The main treatment for ehrlichiosis is antibiotic therapy. Doxycycline is commonly used and has been proven an effective treatment for the disease. If ehrlichiosis has caused other complications, these may need to be treated separately, using different medications or other therapies to target secondary issues caused by Ehrlichia’s presence. 

In some cases, such as when severe bleeding occurs, intensive care and the ministrations of an internal medicine specialist and/or critical care specialist may be required. Blood transfusions and other intensive supportive therapies may be necessary for these patients.


There is currently no vaccine against ehrlichiosis. Appropriate tick-control methods combined with routine periodic testing is the best way to help protect those dogs inevitably exposed to ticks.

Limiting a dog’s exposure to wooded areas or other places where ticks may hide can help reduce the risk of infection. Frequently checking a dog for ticks and safely removing them is an important daily routine, particularly during tick season.

This article has been reviewed by a Veterinarian.