Flu-like illness with leukopenia, thrombocytopenia, and elevated serum transaminases in a patient with a recent tick bite; [CCDM]
1. Ehrlichosis is caused by obligate, intracellular bacteria living in phagosomal vacuoles and may be seen on blood smears as "morulae" in the cytoplasm of monocytes or neutrophils.
2. Human monocytic ehrlichiosis (HME) is caused by Ehrlichia chaffeensis. Human granulocytic anaplasmosis (HGA) is caused by Anaplasma phagocytophilium. Ticks are the vectors for HME and HGA. Meningoencephalitis is present in about 20% of patients. The Japanese form of ehrlichiosis (Sennetsu fever) resembles mononucleosis with sore throat, increased lymphocytes, and enlarged cervical lymph nodes. Neoehrlichia mikurensis infection has recently been described in Europe and Asia among the immunocompromised. [CCDM, p. 183-4]
3. The agents causing ehrlichiosis are related to the genus Rickettsia. HME complications include meningoencephalitis, shock, respiratory distress, and acute renal failure. In one series of cases, 26% of the patients with HME had a rash. Thrombocytopenia, leukopenia, and elevated liver transaminases are characteristic of HME and HGA infections. The case-fatality rate was 3% for HME and <0.5% for HGA. Complications for HGA include shock, seizures, pneumonitis, hemorrhage, rhabdomyolysis, and acute renal failure. Serological surveys show that organisms similar to E. chaffeensis infect humans in Europe, Africa, and Latin America. [Guerrant, p. 339-43]
4. Most HME infections are not diagnosed, but 8386 cases were reported to the CDC between 1987 and 2012. Hospitalization is required in about 49% of cases, and at least 9% of cases are life threatening. Leukopenia is usually in the range of 1300-4000 cells/microliter, and thrombocytopenia is usually in the range of 50,000-140,000 platelets/microliter. Between 1995 and 2012, 10,152 cases of HGA were reported to the CDC. Rash is present in less than 10% of cases, but most of these are thought to be due to concurrent infection with Lyme disease (erythema migrans). Morulae can be seen in neutrophils in about 20-80% of patients. [PPID, p. 2229-32]
5. The rare human ewingii ehrlichiosis mainly infects canines, but cases in immunocompromised patients have been reported mostly in Missouri, Oklahoma, and Tennessee. [ABX Guide: Ehrlichia species]
6. The Ixodes scapularis ticks that carry Lyme disease may also carry human granulocytic anaplasmosis (HGA) and babesiosis. [IDSA Guidelines. Clinical Infectious Diseases. 2006;43:1089-1134]
7. In HME, rash may rarely affect the palms and soles. [PPID, p. 744]
8. Ehrlichiosis is in the differential diagnosis of rash and splenomegaly/hepatomegaly. [Guerrant, p. 955]
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Paired sera (4-fold rise), or >1:256 IFA titer, or PCR detection; Probable case if IFA titer 1:64-128; [ABX Guide: Ehrlichia species]