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by Holly Frisby, DVM
Canine ehrlichiosis is a disease of dogs and wild canids (e.g., wolves) and is found worldwide. Canine ehrlichiosis is also known by other names such as "tracker dog disease", "tropical canine pancytopenia", "canine hemorrhagic fever", and "canine typhus". It affected a large number of military dogs in the war in Vietnam.
What causes ehrlichiosis? Ehrlichiosis can be caused by several organisms including Ehrlichia canis, E. equip, E. platys, E. ewingii, and possibly others. The Ehrlichia organisms are what we call rickettsia which on the evolutionary scale are between bacteria and viruses. How is Ehrlichia transmitted? Ehrlichia is transmitted by the brown dog tick, Rhipicephalus sanguineus. The immature form of the tick feeds on an animal infected with Ehrlichia. When these immature forms or a mature form of the tick feeds on another animal, the Ehrlichia is passed on to that animal. The Ehrlichia can remain alive in the developing tick for up to 5 months. This means a tick could become infected in the fall, and infect a dog the following spring. Because the disease is transmitted by the brown dog tick, it can occur wherever brown dog ticks are found. Almost every state in the United States has reported a case of ehrlichiosis. What are the symptoms of ehrlichiosis? Ehrlichiosis can have three phases. Signs of the acute phase of the disease usually develop 1-3 weeks after the bite of the infected tick. The acute phase of the disease generally lasts 2-4 weeks. The Ehrlichia enter certain cells of the body and reproduce inside of them. These cells are found in the lymph nodes, spleen, liver, blood, and bone marrow. As a result of the infection the lymph nodes, liver and spleen are often enlarged. Anemia, fever, depression, lethargy, loss of appetite, shortness of breath, joint pain and stiffness, and bruises are often seen. In the sub clinical phase the animal may show only slight anemia. During this phase the dog either eliminates the Ehrlichia from the body or the infection may progress to the chronic phase. The chronic phase generally develops 1-4 months after the tick bite and can be either mild or severe. Weight loss, anemia, neurological signs, bleeding, inflammation of the eye, edema (fluid accumulation) in the hind legs and fever may be seen. Blood tests show that one or all of the different blood cell types are decreased. One cell type, the lymphocyte may increase and be abnormal in appearance. This can sometimes be confused with certain types of leukemia. If a dog becomes chronically infected, the disease can keep coming back, especially during periods of stress. A decrease in the number of platelets (platelets help the blood clot) in the blood is the most common laboratory finding in all phases of the disease. Changes in the protein levels in the blood are common. The most common protein, albumin, is decreased and other types of protein called "globulins" are increased. Since one tick could be infected with and transmit more than one disease (e.g., haemobartonellosis or babesiosis), it is not all that uncommon to see a dog infected with more than one of these diseases at a time which generally causes more severe symptoms. How is ehrlichiosis diagnosed? A highly accurate blood test which tests for the dog's antibodies (proteins produced to fight off the infection) to Ehrlichia is available. It is called the indirect immunofluorescent antibody (IFA) test. The antibodies may not be detected in the early phase of the disease since it takes some time for the body to make them. As the disease progresses, the antibody level will rise significantly. Often two tests will be done 2 weeks apart and the results compared. Dogs with an active infection will show a significant rise in the amount of antibody present. A newer test called the ELISA test is becoming more available and the test can be run in your veterinarian's laboratory. This test also determines the amount of antibodies present. The antibodies can last for one or more years after the infection, but they do not make the dog immune to ehrlichiosis - the dog could get re infected. Sometimes the organism can be seen inside cells on a blood smear. To find them, a small drop of blood is spread over a microscope slide, stained and examined under the microscope. The organism can only be found in the blood stream for about 3 days during the acute phase of the disease. So this method of diagnosis could miss some cases of the disease. How is ehrlichiosis treated? The antibiotics tetracycline or doxycycline are used. Treatment is for 2-3 weeks. Some dogs will need blood transfusions or intravenous fluids depending on the severity of the disease. Generally the prognosis during the acute phase is good if the animal is properly treated. Dogs who go on to the chronic phase have a poorer prognosis. German shepherds and Doberman pinschers tend to have a more severe chronic form of the disease. The drug imidocarb dipropionate is sometimes used in conjunction with the antibiotics. It is given as an injection, but may not be available in all areas. Some of the damage caused by Ehrlichia may be due to the dog's own immune response to the organism. For this reason, high doses of corticosteroids (e.g., prednisolone) are often given during the early phase of the disease. How can I prevent ehrlichiosis in my pet? Tick control is the main way to prevent ehrlichiosis. Products which repel and kill ticks such as Biospot for Dogs are excellent choices. Tick collars containing the active ingredient amitraz (Preventic collars) are also used, sometimes in conjunction with Biospot in those areas with high tick infestations. If a large number of cases of ehrlichiosis are diagnosed in an area, some veterinarians recommend placing dogs on low doses of tetracycline or doxycycline during the tick season. There is no vaccine for ehrlichiosis. Can people get ehrlichiosis? Yes. The common symptoms in people include fever, chills, headache, and muscle aches. Other less common symptoms include nausea, loss of appetite, weight loss, abdominal pain, cough, diarrhea and change in mental status. People do NOT get infected directly from a dog, but through a tick bite. Human ehrlichiosis may be spread by a different tick than the brown dog tick. Research suggests the Lone Star tick may be involved. Also, the Ehrlichia species most often implicated in human infections is E. chaffeensis. References Couto, DG. Rickettsial Diseases. In Birchard, SJ; Sherding, RG (eds): Saunders Manual of Small Animal Practice. WB Saunders Co., Philadelphia PA; 1994;124-5. Harrus, S; Bark, H; Waner, T. Canine monocytic ehrlichiosis: An update. Compendium of Continuing Education for the Veterinary Practitioner 1997;19 (4) :431-444.
Olson, JG. Ehrlichiosis. In: Zoonoses updates from the Journal of the American Veterinary Medical Association. American Veterinary Medical Association, Schaumburg IL; 1995:74-75.
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