Human Granulocytic Ehrlichia Infection in Belgium

B. Guillaume (1), P. Heyman (2), C. Vandenvelde (2), M. Delmée (1), G. Bigaignon (1).

(1) Department of Microbiology, University of Louvain, Brussels, Belgium. (2) Research Laboratory for Vector-borne diseases, Queen Astrid Military Hospital, Brussels, Belgium.

Email: paul.heyman@smd.be

The causative agent of the human granulocytic Ehrlichiosis (HGE), a tick-borne zoonosis, is a gram-negative obligate intracellular bacterium that invades granucolytic leukocytes. The severity of the disease may range from subclinical seroconversion to fatal illness. The first case of HGE has been reported in 1994 from the United States, since 1995 serological evidence for HGE infection has been demonstrated in several European countries. There is substantial evidence that Ixodes ticks are the main vector for the HGE agent; Ixodes scapularis in the United States and Ixodes ricinus in Western Europe.

We investigated the presence of antibodies against the HGE agent in 228 serum samples from patients with clinical and serological evidence of infection by Borrelia burgdorferi, using immunodiagnostic methods; i.e. indirect immunofluorescent assay (IFA) where we applied three types of antigens for IgG and IgM detection; E. chaffeensis, the agent for HGE and E. equi and Western Blot (WB) where we used IgG and IgM HGE specific tests.

In IFA we found 17 sera (7.5%) with a titer of 1:64 or more for the HGE agent, 15 were IgG positive and the remaining two were IgM positive. Confirmation by HGE-specific WB was performed on all available IFA HGE-positive serum samples (16/17), seven (43.7%) showed a distinct band for rP44.

Indirect immunofluorescent assay is no doubt the most widely used method for serodiagnosis of HGE infection and although the method is sensitive, it suffers from drawbacks as there is the subjective reading and the specific problems of cultivation of whole infected cells, i.e. possible changes in the antigenic composition during passage and the risk of an increased false positive reaction rate due to non-specific antibody binding reactions and antigenic cross-reactivity. In contrast, the use of recombinant HGE specific antigenic P44 protein seems to provide more specificity and lacks genogroup cross-reactivity, the cross-reactive antigens are found in the size range of 55 to 60 kDa rather than 44 kDa.

Our results show evidence of the exposure to the HGE agent in 17 patients by IFA and we were able to confirm these findings in seven out of the 17 patients by WB. To our knowledge, this is the first time that the presence of the HGE agent, as human pathogen and as co-infection with Lyme disease, was demonstrated in Belgium.

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