Ehrlichiosis: What You Should Know About This Tick-Borne Disease

American dog tick
Three ticks are known to spread Ehrlichia spp., the organism that causes: the brown dog tick, the American dog tick and the lone star tick.

Ticks are trouble! We all know that they spread the bacteria that cause Lyme disease, but another tick-borne disease that is steadily increasing is ehrlichiosis. Once limited to western Texas, Oklahoma and Missouri, the incidence of ehrlichiosis is expected to rise in those areas, as well as in southern California and the southeastern United States, according to the Companion Animal Parasite Council.

Dogs with ehrlichiosis can develop an acute infection that starts with fever, appetite loss and lethargy. Two to four weeks after experiencing the bite of an infected tick, a subclinical infection can set in, causing thrombocytopenia. That $5 word means that the dog doesn’t have enough platelets in his blood. When that happens, he can experience bleeding into body tissues (known as petechiae) and bruising. His blood may clot more slowly than normal after an injury. Bone marrow suppression is often a result of chronic Ehrlichia spp. (the "spp." refers to all species of this type of bacteria) infection. It can appear months to years after a tick bite. Certain breeds — in particular, German Shepherds — tend to be predisposed to severe forms of ehrlichiosis.

Cats with the disease may show similar signs. Other signs seen in cats and dogs include weight loss, joint pain, vomiting and diarrhea.

How It’s Spread

Three tick species are known to spread the organism that causes ehrlichiosis. The brown dog tick (Rhipicephalus sanguineus), found throughout the United States, is the primary culprit, but the American dog tick (Dermacentor variabilis) and the lone star tick (Amblyomma americanum) 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. 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.

Dogs (and cats) become infected with Ehrlichia spp. when infected ticks feed on them, injecting the bacteria into their blood by deeply burying their mouthparts into the skin. Nasty!

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 doxycycline is a good clue that your veterinarian has found the cause of your dog’s symptoms.


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