Investigations of rabies in Berlin and the effect of oral immunisation of foxes

The objective of the study was to estimate the incidence of rabies, in the metropolitan area of Berlin, in the period 1985-1995, and to analyse the re asons for the development of an epidemic in relation to the measures used t o control rabies. A total of 6,687 domesticated and free-living species wer e examined for rabies virus infection, resulting in a prevalence of 31.7%. This indicated the ability of the fox population in Berlin to exploit this ui-ban habitat successfully. The presence of field virus antigen was detect ed in 218 (3.2%) domesticated and free-living species by an immunofluoresce nce assay. Of all recorded cases of rabies, 15.6% were detected in domestic animals and 84.4% in free-living species. The greatest prevalence of rabie s was in foxes with 64.7% of all cases in wildlife species. The greater pre valences of rabies in the autumn and winter are consistent with the demogra phic characteristics of the fox population. The observed prevalence of rabi es infection in other wildlife increased approximately 1 month after the pe ak in the prevalence within the fox population. A temporal periodicity in t he prevalence of fox rabies with several years between peaks was observed i n Berlin until 1989. Although there was a physical barrier between West Ber lin and the former German Democratic Republic, it is apparent that animals were able to cross the border and introduce rabies into West Berlin. The ma rked increase in the prevalence of rabies since 1990 is associated with the opening of this frontier: This occurred in the autumn, of 1989, the season of maximum mobility within the fox population, resulting in an acceleratio n of the introduction of I-abies in West Berlin at this time. The oral vacc ination of foxes, using baits, started in West Berlin in 1988, and the whol e urban area was involved by 1991. This control measure has proved to be ef fective. Following two vaccination campaigns, in 1988 and in 1989, the rate of seroconversion achieved was greater than that suggested by experts for vaccination to be effective. Although the fox population of West Berlin has been subjected to a vaccination campaign, the opening of the frontier and the consequent immigration of non-vaccinated foxes resulted in the greatest prevalence of rabies in foxes, in 1990 and 1991, since 1954. As a result a semi-circular vaccination zone was established around the area of West Ber lin in the autumn of 1990. Then, in 1991 a vaccination campaign was impleme nted in East Berlin. As a result, the seroconversion rates in foxes increas ed. The systematic widening of the vaccination areas in the eastern part of Germany has resulted in the application of more geographically uniform rab ies control measures with the reduction of fewer cases of rabies being intr oduced into the metropolitan area of Berlin. Even with this control strateg y, it is necessary to continue with the hunting of foxes to enhance the suc cess of the oral vaccination strategy and to protect small game and endange red species.