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Diagnosis, treatment of tick-borne diseases
Some cases difficult to detect or fail to respond to therapies


DVM360 MAGAZINE


Ehrlichiosis/anaplasmosis

Canine ehrlichiosis/anaplasmosis is caused by several different species of Ehrlichia/Anaplasma species. Those species reported in the United States include E. canis, E. ewingii, E. chaffeensis, A. phagocytophilum (E. equi) and A. platys (E. platys). Ehrlichiosis can be either acute or chronic. Most cases are recognized during the chronic stage.

The hematologic effects of ehrlichiosis/anaplasmosis can be variable, but the most common abnormality detected is thrombocytopenia. Despite the fact that many veterinarians suspect ehrlichiosis/anaplasmosis in dogs with any hemolytic anemia, a non-regenerative anemia is more commonly identified. Ehrlichiosis is only occasionally associated with a secondary IMHA.

Ehrlichiosis also can cause pancyto-penia. The effects on the leukon are variable. Both leukocytosis and leukopenia do occur. Lymphocytosis can be seen. The accompanying clinical signs often are vague, including fever, lethargy, anorexia, weight loss and vomiting. Bleeding tendencies such as epistaxis, petechia or ecchymosis also may be present. Hyperglobulinemia (polyclonal much more commonly than monoclonal), hypoalbuminemia, lymphadenopathy, proteinuria, polyarthritis (common with E. ewingii) and/or uveitis may be present.

The absence of thrombocytopenia does not rule out ehrlichiosis. Anaplasma platys only appears to cause thrombocytopenia and not systemic illness. Anaplasma phagocytophilum is associated with acute febrile illness in dogs and thrombocytopenia is a common finding. Co-infection with A. phagocytophilum and Borrelia burgdorferi has been associated with worse illness.

Serology is helpful in the diagnosis of ehrlichiosis/anaplasmosis. Acute and convalescent (three to four weeks) titers should be performed if the clinical signs are acute and initial titers are low or negative.

A four-fold change is consistent with ehrlichiosis/anaplasmosis. If the signs are chronic (> four weeks), then a single high titer is consistent with infection. In-house tests are not designed for diagnostic use but a positive test in conjunction with appropriate clinical findings is supportive of a diagnosis of ehrlichiosis/anaplasmosis.

The current in-house assays fail to detect antibodies against E. ewingii and cannot differentiate antibodies against A. phagocytophilum from those against A. platys. Occasionally a morula is identified in a white blood cell or platelet on a blood smear, but the parasitemia often is very low, so the sensitivity of microscopy is poor. The low levels of circulating organisms also can hamper PCR. A positive PCR test should rule in the presence of infection and identify which species is present. A negative PCR test does not rule out the possibility of ehrlichiosis. Therefore, the resolution of clinical signs in response to therapy remains an important "test."

Doxycycline (10 mg/kg/day for three to four weeks) is considered the treatment of choice. Other drugs that are reported to be effective include tetracycline, oxytetracycline, minocycline and chloramphenicol. Imidocarb dipropionate does not appear to be an effective treatment.

Resolution of clinical signs after therapy is probably the most important follow-up; further specific diagnostics for ehrlichiosis/anaplasmosis are not indicated.

Serology generally is a poor way to assess recovery because antibody titers may persist for months. If the animal is seroreactive and does not respond to therapy, the PCR should be performed because some species, such as E. chaffeensis, may not respond as well to therapy. If the PCR is negative, then an alternative diagnosis should be considered. Dogs do not appear to transmit infections to humans but can act as a sentinel for ehrlichiosis/anaplasmosis.

The clinical signs of feline ehrlichiosis appear similar to what is seen in dogs, and it should be considered when more common causes of disease are not apparent.


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Source: DVM360 MAGAZINE,
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