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Isolation and characterization of an Ehrlichia sp. from a patient diagnosed with human ehrlichiosis
J E Dawson1, B E Anderson, D B Fishbein
1Division of Viral and Rickettsial Diseases, Centers for Disease Control, Atlanta, Georgia 30333.
Abstract:
A new disease was recognized in the United States in 1986. The etiologic agent, although not previously isolated from a human, appeared to be serologically related to Ehrlichia canis, a canine leukotropic rickettsia. We obtained blood specimens from 27 febrile patients with a history of tick exposure. Leukocytes from 24 patients not treated with tetracycline were placed onto a monolayer of DH82 cells. We performed indirect immunofluorescence on sera from all 27 febrile patients as well as sera from 12 patients with previously diagnosed ehrlichiosis. Intractoplasmic inclusions were first observed in culture 35 days after the addition of infected blood from one patient. Partial sequencing of the rRNAs from the human isolate and E. canis indicated that they are 98.7% related. Positive indirect immunofluorescence reactions to the human isolate were obtained for all 12 previously diagnosed patients and for 33% of the 27 febrile patients. Two patients were seropositive for the human isolate but not for E. canis. No sera were positive for E. canis and negative for the human isolate. We report the isolation of a previously unrecognized Ehrlichia sp. that appears to be the etiologic agent of human ehrlichiosis. Serologic data (range of antibody titers, 256 to 32,768) in combination with rRNA sequencing indicated that the newly isolated Ehrlichia sp. is similar, but not identical, to E. canis.
Insights
A novel Ehrlichia species, serologically related to Ehrlichia canis, was isolated from human patients in the US. This discovery identifies the causative agent of a previously unrecognized human ehrlichiosis.
Area of Science:
- Microbiology
- Infectious Diseases
- Veterinary Medicine
Background:
- Human ehrlichiosis emerged as a distinct disease in the United States in 1986.
- The suspected etiologic agent showed serological similarities to Ehrlichia canis, a known canine pathogen.
Observation:
- Blood samples from 27 febrile patients with tick exposure were analyzed.
- Leukocytes from untreated patients were cultured, and intracellular inclusions were observed after 35 days.
- Indirect immunofluorescence assays were performed on patient sera.
Findings:
- A previously unrecognized Ehrlichia species was isolated from human patients.
- Partial rRNA sequencing revealed 98.7% relatedness between the human isolate and Ehrlichia canis.
- Serological tests confirmed a strong relationship to Ehrlichia canis, with some patients positive for the human isolate but not E. canis.
Implications:
- This study reports the isolation and characterization of the etiologic agent of human ehrlichiosis.
- The findings suggest a close relationship between the human Ehrlichia species and Ehrlichia canis.
- Further research is warranted to understand the transmission and pathogenesis of this emerging infectious disease.