NAMES OF DISEASE:         Ehrlichiosis
                                               Sennetsu fever
                                               Sennetsu rickettsiosis

ETIOLOGICAL AGENTS:     Ehrlichia canis
                                               Ehrlichia sennetsu
                                               Ehrlichia chaffeensis
                                               Ehrlichia equi
                                               Ehrlichia phagocytophilia

EPIDEMIOLOGY:

    The disease is transmitted by the bite of a tick, but the species of the tick is unknown. The reservoir is the domestic dog and perhaps the coyote and wolf.

PATHOLOGY:

    There is a 12-day incubation period during which time it can be found in the blood, lymph nodes and bone marrow. However, the primary target tissue is the leukocyte. The organism is an obligate intracellular parasite which multiples within the cytoplasm of the host cell. Like the Rickettsia, and in contrast to Coxiella, it does not form a vacuole within the cytoplasm. There are characteristic intracytoplasmic inclusions within the leukocyte that are used for diagnosis. There is a leukopenia and thrombocytopenia. In a few people there is a maculopapular or petechial rash, but this is rare.

MANIFESTATIONS:

    The symptomology is similar to that of Rocky Mountain spotted fever without the rash, i.e., there is a high fever, toxicity, and myalgia.
 

DIAGNOSIS:

    Diagnosis is based on the finding of intracytoplasmic inclusions in lymphocytes, monocytes and neutrophils or by detecting antibodies to the Ehrlichia antigens.
 

TREATMENT:

    Tetracycline