Ehrlichia chaffeensis, E ewingii, and an E muris-like pathogen have been identified as causes of human ehrlichiosis in the United States. E chaffeensis is the most common cause of human ehrlichiosis, but reported E ewingii infections are on the rise. E ewingii diagnosis, dependent on species-specific molecular testing, may be underreported.
The goal of this study was to determine geographic distribution and clinical characteristics of PCR-confirmed human E ewingii infections in the United States. After retrospectively reviewing PCR test results for ehrlichiosis over 18 months, the authors subjected samples positive for E ewingii and/or E canis not differentiated in the original PCR to additional PCR testing to distinguish between them. E ewingii and/or E canis-positive cases accounted for 10 of 109 ehrlichiosis cases; all 10 were then identified as E ewingii. This is a higher rate of infection (9.2%) with E ewingii than previously reported, with cases reported for the first time in New Jersey and Indiana. (The other 99 samples were positive for E chaffeensis.)
The 5 E ewingii cases highlighted in this study reported classic ehrlichiosis symptoms (eg, headache, malaise, fever, myalgia). Thrombocytopenia and leukopenia were also commonly reported. All 5 patients improved with doxycycline treatment. The authors concluded that E ewingii should be considered an agent of tick-borne febrile illness in humans in the central and eastern United States.