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Examination of bats for rabies in Styria
Abstract
Since rabies was diagnosed in bats in 11 European countries during the last decades, and there are no data published for Austria, we have looked for rabies virus and viral antigen in 40 bats, originating from the federal state of Styria, which had died spontaneously. All proved negative. In addition, we present in this paper the epidemiology of bat rabies in Europe, and discuss a potential risk associated with handling of European bats.
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Cell-mediated immunity induced by rabies vaccination was studied in humans by the determination of specific interleukin-2 (IL-2) production in a large number of donors (postexposure immunized patients and pre-exposure immunized laboratory workers). Peripheral blood lymphocytes (PBL) from 35 donors were tested for IL-2 production after in vitro stimulation by different rabies and rabies-related viruses. IL-2 responses were compared to antibody recognition of these different virus serotypes by sera from the same individuals. IL-2 was produced by PBL from more than 85% of donors after stimulation with inactivated and purified rabies viruses (IPRV) prepared from either Pittman Moore (PM) or Pasteur Virus (PV) strains. IL-2 was also produced by 65 and 45% of donor PBL stimulated with IPRV from the European Bat Lyssavirus (EBL) and Mokola (Mok) rabies-related virus strains respectively. No correlation was found between the production of IL-2 by PBL and the levels of virus neutralizing antibody (VNAb). Moreover, 50, 25 and 35% of donors produced IL-2 after stimulation of their PBL with ribonucleoprotein (RNP) from PV-, EBL- and Mok-viruses, respectively. These results obtained with a large number of human rabies vaccinees and using an assay specific to T-cell activation confirm the significant cross-reactivity of T-cell responses directed against rabies and rabies-related viruses. This study shows that IL-2 production could be used for the study of cell-mediated immunity and T-cell memory induced in humans by rabies vaccination.
Protection experiments were performed in mice with different inactivated vaccines prepared with the fixed rabies virus strains: PM (Pitman-Moore), PV4 (Pasteur virus) and LEP (Flury LEP) against an intracerebral challenge with a European bat virus (Duvenhage, strain Hamburg, DUV3). All vaccines protected mice against challenge with CVS (Challenge virus standard). Vaccines prepared with PV4 protected mice against a DUV3 challenge. On the contrary, PM or LEP vaccines did not protect mice against a DUV3 infection. The protection conferred by PV4 vaccines against Duvenhage could be due to the antigenic relationship which seems to exist between PV4 and European bat virus as revealed by serum-virus neutralization, absorption experiments and CTL crossreactivity. The four virus strains PAS, PV4, PM and CVS, originated from the Pasteur virus isolated in 1882 from the brain of a rabid cow, were classified in two groups on the basis of reactivity with neutralizing anti-glycoprotein monoclonal antibodies. One group contained the L. Pasteur (PAS) and the PV4 strains, the second contained PM and CVS strains. The divergence between the two virus groups possibly resulted from distinct passage histories.
In 1985, a notable increase in the number of recorded cases of rabies in European bats was observed, indicating a possible spread of the rabies virus in these bats. Because of concern that the disease could be introduced into the United Kingdom by bats crossing from mainland Europe, a programme of screening dead bats for the presence of rabies and rabies-related viruses was initiated at the Rabies Research and Diagnostic Unit at the Central Veterinary Laboratory. Over a period of 10 years (January 1986 to December 1995), 1882 bats belonging to 23 species from all parts of England, Scotland and Wales have been screened for rabies antigen. All of these bats were found to be negative. Forty-one serotine bats (Eptesicus serotinus), the species of bat most commonly infected in Europe, were included in the total. Subsequent to this survey, in June 1996, a European bat lyssavirus 2 was isolated from a Daubenton's bat (Myotis daubentonii) in Newhaven, East Sussex. It is possible that this bat originated from mainland Europe but this cannot be established with certainty.