Human monocytic ehrlichiosis
| Pathogen: Ehrlichia chaffeensis |
| Tick vectors: Primarily Amblyomma americanum |
| Geographic distribution: Southeastern, south-central, and mid-Atlantic regions |
| Classic presentation: Fever, headache, myalgia, malaise, cough, gastrointestinal symptoms, rash, meningitis, thrombocytopenia, leukopenia, lymphopenia, anemia, hyponatremia, elevated aminotransferase levels; laboratory abnormalities may no longer be present after 1 week of symptoms |
| Diagnosis: Polymerase chain reaction assay available; 4-fold increase between acute and convalescent serology with a minimum peak titer ≥ 1:64; morulae in monocytes on Giemsa- or Wright-stained peripheral smear; cell culture rarely used |
| Treatment: Doxycycline, typically for 7–14 days |