Ehrlichiosis: An acute (abrupt onset) disease, first reported in humans in 1986, due to infection by the rickettsial agent, Ehrlichia canis. The brown dog tick, is the common vector (carrier).

Ehrlichiosis is clinically similar to Rocky Mountain spotted fever with high fever, headache, malaise, and muscle pain but without a rash.

Laboratory features include leukopenia (low white blood cell count), thrombocytopenia (low platelet count), mild anemia, and elevation in the levels of hepatic aminotransferase enzymes.

Clinical symptoms and laboratory abnormalities respond promptly to therapy with the antibiotics tetracycline or doxycycline, and the majority of patients become afebrile within 24 to 48 hours after the start of such treatment.

The diagnosis of ehrlichiosis rests on the detection of ehrlichia either by direct means or by the indirect means of serologic studies. Three methods are available for detection: inspection of peripheral-blood smears, PCR testing, and tissue culture.

The disease ehrlichiosis is named for the great German Nobel Prize winning physician and bacteriologist Paul Ehrlich (1854-1915).