Ehrlichiosis occurs commonly in the United States. Human monocytic ehrlichiosis occurs in broad areas across the southeastern, south central, and Mid-Atlantic United States in a distribution that parallels that of Rocky Mountain spotted fever. Anaplasmosis is found mostly in the northeastern and upper midwestern United States, but infections have now been identified in northern California, the Mid-Atlantic states, and broadly across Europe.
Human monocytic ehrlichiosis, anaplasmosis, and Ehrlichiosis ewingii cause similar acute febrile illness characterized by fever, malaise, headache, myalgias, anorexia, and nausea, but often without a rash. In contrast to adult patients, nearly two thirds of children with human monocytic ehrlichiosis present with a macular or maculopapular rash, although petechial lesions may occur. Symptoms usually last for 4 to 12 days.
Characteristic laboratory findings include leukopenia, lymphocytopenia, thrombocytopenia, anemia, and elevated hepatic transaminases. Morulae are found infrequently in circulating monocytes of persons with human monocytic ehrlichiosis but are found in 40% of circulating neutrophils in 20% to 60% of persons with anaplasmosis (Fig. 122-2). Seroconversion or fourfold rise in antibody titer confirms the diagnosis.
Ehrlichiosis is clinically similar to other arthropod-borne infections, including Rocky Mountain spotted fever, tularemia, babesiosis, early Lyme disease, murine typhus, relapsing fever, and Colorado tick fever. The differential diagnosis also includes infectious mononucleosis, Kawasaki disease, endocarditis, viral infections, hepatitis, leptospirosis, Q fever, collagen vascular diseases, and leukemia.
As with Rocky Mountain spotted fever, therapy for suspected ehrlichiosis should not be postponed pending results of diagnostic tests. Ehrlichiosis and anaplasmosis are treated with doxycycline.
Figure 122-2 A morula (arrowhead) containing Anaplasma phagocytophilum in a neutrophil. Ehrlichia chaffeensis and A. phagocytophilum have similar morphologies but are serologically and genetically distinct. (Wright stain, original magnification X 1200.) (From Walker DH, Dumler JS: Ehrlichia chaffeensis (human monocytotropic ehrlichiosis), Anaplasma phagocytophilum (human granulocytotropic anaplasmosis), and other ehrlichieae. In Mandell GL, Bennett JE, Dolin R, editors: Principles and Practice of Infectious Diseases, ed 6, Philadelphia, 2005, Churchill Livingstone, Fig. 190-2, p 2315.)
Severe pulmonary involvement with acute respiratory distress syndrome has been reported in several cases. Other reported severe complications include meningoencephalitis and myocarditis. Most patients improve within 48 hours.
Preventive measures to avoid tick-borne infections and careful removal of ticks are recommended.
Protozoa are the simplest organisms of the animal kingdom. They are unicellular. Most are free living, but some have a commensal or parasitic existence. Protozoal diseases include malaria, toxoplasmosis, babesiosis, and the intestinal protozoal diseases, amebiasis, cryptosporidiosis, and giardiasis.