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.
How It’s Spread
Three tick species are known to spread the organism that causes Ehrlichiosis. The brown dog tick (Rhipicephalus sanguineus)(See image beside), found throughout the United States and Canada, is the primary culprit, but the American dog tick (Dermacentor variabilis) and the lone star tick (Amblyomma americanum) (New Specie in Canada), can also transmit the bacteria that cause disease. You might think lone star ticks would be limited to the Lone Star State (Texas, of course), but they are found up from the southeastern U.S. and Texas through the Mid-Atlantic Seaboard all the way to New England, and since last year, it’s being identified as a new specie in Canada.
American dog ticks reside east of the Rockies, mainly in areas such as grassy fields, walkways and trails. They can survive for two or more years without a host.
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.
It can take as little as three to six hours for ticks to transmit the bacterial invaders. Once the bacteria enter the blood cells, they thrive, multiply and spread throughout the body. The disease is diagnosed based on a history of tick exposure, presence of signs, a platelet count and a positive blood test result for the bacteria that cause the disease: Ehrlichia canis (the primary cause in dogs), Ehrlichia ewingii (seen in dogs and humans) and Ehrlichia chaffeensis (the primary cause in humans). Ehrlichiosis isn’t always easy to diagnose, because it can take time for antibodies to develop, but response to treatment with antibiotics can be a clue that your veterinarian has found the cause of your dog’s signs.
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 (We have available this test at our clinic). This 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.
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, and frequently checking your dog for ticks and safely removing them is an important daily routine, particularly during tick season.
This blog was written by McQueen Animal Hospital, an animal clinic (vet hospital/vet clinic) in Brampton committed to providing only the highest level of veterinary care to our beloved pets.