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Ehrlichiosis
Ehrlichiosis is caused by the rickettsial organism Ehrlichia canis. Other examples of rickettsial organisms are Riskettsia rickettsi, which causes Rocky Mountain Spotted Fever and Ehrlichia risticii, which causes Potomac Fever in horses. These organisms tend to be carried by ticks and other insect vectors, in some cases. For ehrlichiosis, the most common vector is the brown dog tick. For this reason, ehrlichiosis occurs anywhere this tick occurs. At present, it has been reported in 34 states, with the northern states being spared in most instances. The southeastern and south central states are the most heavily affected. A few cases of Ehrlichia canis infection have been reported in people after tick bites.
Ehrlichia infection can cause a number of clinical signs. It can be extremely hard to diagnose due to the wide range of symptoms that can occur. Most dogs infected with this organism will have be lethargic, lose weight, show less interest in food and become anemic. Other possible clinical signs include hemorrhages under the skin or in around the gums, swollen lymph nodes, muscular or joint soreness, nasal discharges or nosebleeds, severe neck or back pain, blood in the urine and eye problems ranging from exudates to severe inflammation of the internal eye structures. Neurologic signs such as seizures and difficulty walking can occur. Respiratory or heart related signs can occur due to hemorrhaging and compensation for anemia if it becomes severe. Hemorrhaging occurs primarily due to decrease in platelet counts from the infection. While most dogs show a number of symptoms when first infected with Ehrlichia, there is also a chronic infection that can occur if the acute infection is not treated. In this case, the dog may appear to be normal or may show vague signs of illness occasionally. This is one cause of the complaint that "my dog just isn't doing right". The chronic illness can suddenly become very severe again if the dog is stressed in some manner or become less immune competent for some reason.
The best method of diagnosing this disease is through testing of serum from the dog using an immunofluorescent antibody (IFA) test. unfortunately, a positive test only indicates exposure. Still, in the presence of clinical signs or if the titer rises after treatment or stays consistently high, infection is strongly implied by the lab results.
Ehrlichia canis is normally susceptible to treatment with tetracycline antibiotics, including doxycycline. In some situations the organism will not respond to these antibiotics or their use is contraindicated due to the young age of a dog or pregnancy. In this case, chloramphenicol can be used and there is anecdotal evidence of success using cephalosporin antibiotics. The bleeding tendencies in this disease are related to a drop in platelets (thrombocytopenia) so it can be necessary to use corticosteroids to treat this condition if the platelet counts are low. While this can be life saving, the use of corticosteroids should be discontinued as quickly as possible so that their immunosuppressive effect does not interfere with successful treatment. Extensive supportive care, including intravenous fluids, administration of blood products and hospitalization may be necessary to treat this problem in some dogs. The survival rate is good if the disease is recognized and treated aggressively.
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Last edited 01/13/08