Ehrlichia in animals and humans

University dissertation from Dept of Medical Microbiology, Dermatology and Infection

Abstract: Ehrlichia phagocytophila is a tick-borne pathogen of domestic animals, which has recently been acknowledged also as a human pathogen. It is a strictly intracellular bacterium, infecting granulocytes of the host, sometimes resulting in clinical disease - granulocytic ehrlichiosis - with manifestations ranging from mild flu-like conditions to severe infections with multi-organ failure and death. This thesis probes into four main aspects of E.phagocytophila and granulocytic ehrlichiosis, namely the isolation and characterisation of Swedish strains, the pathogenesis in an animal model, the seroprevalence of antibodies to ehrlichia in tick-exposed human populations, and the prospective monitoring of clinical cases of granulocytic ehrlichiosis in animals and humans. Main findings include the isolation and propagation of E.phagocytophila in cell-line culture, and partial genetic characterisation of those isolates and other clinical strains of E.phagocytophila. Comparison of partial sequences of the 16S rRNA and the groESL genes and one gene (ank) coding for a structural protein, of strains of Swedish, Slovenian and North American origin revealed a close relationship, but placed all European isolates in a separate clade. Experimental infection of dogs showed that the most prominent clinical sign of granulocytic ehrlichiosis was fever. Haematological changes occurred in all infected individuals even in those with non-apparent clinical signs. Furthermore, granulocytic ehrlichiosis was established as a clinical entity in cats, and granulocytic ehrlichiosis was verified as a common infection in humans living in tick-infested areas, often as a co-infection with Lyme borreliosis. Six case reports of human granulocytic ehrlichiosis are described in detail and proper approaches to the diagnosis and clinical management of granulocytic ehrlichiosis is discussed. Commercial and in-house E.phagocytophila antigens are evaluated.

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