Tick-Borne Diseases

by Dr. Natalee Holt, DVM


It's the middle of the night. The dogs and cats are peacefully sleeping in their beds. I am jarred awake by a blood-curdling scream. "There's a tick on my leg!" The lights go on. It is my husband and there is in fact a tick on his leg. At some point, he stops jumping around and the tick is removed. I am fairly impressed that something only 3 mm in diameter could make a grown man scream (and dance around and scream some more.) Ticks have power!

Because of the pleasantly warm winter, we are supposed to experience a plague of ticks this spring and summer. The tick must be respected as one of the great vectors of diseases. There are no less than 12 diseases of people found in the United States that are spread by ticks. Because they bite wildlife and people, and they pass diseases between one life stage and the next, ticks are able to keep these diseases prevalent in our lives. Lyme disease always takes the spotlight, especially for pet owners in this part of the country. However, there are several other common tick-borne illnesses that affect dogs in this area; they can be far more severe than Lyme disease.

Ehrlichiosis is a disease that is found all over the country. Ehrlichia is a small bacterium that is transmitted from ticks to dogs. Once inside the dog, the bacteria invade white blood cells. The white blood cells then carry the bacteria all around the body. An affected dog will develop a fever, and severe sicknesses that can affect the brain, kidneys, lungs, red blood cells, and platelets. If untreated, this phase of the disease can resolve on its own, but the dog will remain infected for years. Some dogs will then go on to develop a chronic form of disease in which the bone marrow becomes affected and the white blood cells are no longer made properly. If this happens, the dog will be susceptible to many infections. When caught early, this disease is easily treated with antibiotics. While Ehrlichia is more common in the southern part of the United States, the tick that spreads the disease, the Brown Dog Tick, does live in New England. As a result, we see affected dogs every year.

Anaplasmosis is another little known tick-borne disease which is prevalent in New England. There are several strains of this bacterium which is transmitted by the Deer Tick, the same tick that transmits Lyme disease. When the tick bites the dog, the bacteria enter the body and invade the white blood cells or platelets, depending on the strain. While this sounds similar to Ehrlichia, the manifestation of the disease that it causes tends to be milder. Dogs can have a fever, feel lethargic, and experience muscle and joint pain. Dogs with anaplasmosis will also have a decrease in platelets, the cell that clots the blood. Sometimes a low platelet count is the only sign a dog has Anaplasma. Typically, the platelet count is not low enough to cause any problems, but occasionally the platelet count can be severely affected. It is fairly common to see cases of Anaplasmosis in this area, and fortunately it is easily treated with antibiotics. Unlike Ehrlichia, there does not seem to be a chronic disease state that develops.

Rocky Mountain Spotted Fever is another disease caused by transmission of a bacteria from a tick. The ticks that carry these bacteria are the Brown Dog Tick and the American Dog Tick. This disease is more common in the mid-Atlantic region and the south, but does exist in New England; I have seen several cases in the past few years. Once in the body, the bacteria invade the cells that line the blood vessels. As a result, the blood vessels all over the body become inflamed. As inflamed blood vessel will leak fluid, and as a result, you may notice the dog has swollen legs or build-up of fluid in the skin. Damage of the blood vessels in the liver, kidney, and heart can lead to organ failure. Rocky Mountain Spotted Fever is a serious and life-threatening disease. While the disease can be treated with antibiotics, in some cases the organ damage is too extensive.

While dogs are very susceptible to these diseases, cats tend to be more resistant. Cats may test positive for Ehrlichia or Anaplasma but not show signs of illness. Rarely, a cat will have similar symptoms as a dog and test positive for one of these diseases.

 You may be taking your dog for Lyme vaccines annually, but that vaccine is not effective against Ehrlichia, Anaplasma, or Rocky Mountain Spotted Fever. The only way to prevent these diseases is to limit tick exposure. This includes avoiding tick-infested areas, combing through your dog's fur after taking walks outside, and promptly removing any free or embedded ticks. Application of a topical anti-tick medication should be done religiously during tick season.

Unlike my husband, I do not scream when I find a tick on me. When I lived in the Midwest, I would be able to find ticks of 4 or 5 different species on myself or my dog after a single walk; some ticks actually have beautiful markings. While I do not fear them, I do respect them and the power they have to spread illness. Please be vigilant this season and contact your veterinarian about the best way to protect your dog.      

Originally published in the Hollis Times on July 11, 2012.