Rabies in the Federal Republic of Germany, 1950-81: the Influence of Landscape*
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Bulletin ofthe WorldHealth Organization, 62 (1): 99-106 (1984) © World Health Organization 1984 Rabies in the Federal Republic of Germany, 1950-81: the influence of landscape* H. C. JACKSON' & L. G. SCHNEIDER2 Rabies statistics for 1950-81 were studied to investigate regional differences in the occurrence of rabies in the Federal Republic of Germany. At the level of Landkreis (administrative unit with a mean area of 1013 km ), four basicpatterns ofrabies incidence were identified: insignificant occurrence, low undulations, intermittent peaks, and high oscillations. The distribution of these four epidemiological patterns of rabies was geo- graphically localized. Insignificant occurrence of rabies was found almost exclusively on land under 100 m abovesea level with less than 10% forest cover. High oscillations in rabies occurrence were found most often in areas over 200 m above sea level with an average of at least 35%o forest cover. The current extended epizootic of sylvatic rabies in hunting, fox den gassing, poisoning, and trapping. Europe has affected the Federal Republic of Germany Fox den gassing, in particular, has apparently been for more than 30 years. The disease spread across successful in the short term (8, 14, 17, 18, 25, 28), but eastern Europe during the 1940s and rabies was first rabies has often reappeared within a few years. diagnosed in the Federal Republic of Germany in Indeed, since 1940, Denmark and the Netherlands are Schleswig-Holstein in December 1950. Numerous the only countries in Europe that have become free infections were observed along the eastern border of from the disease for more than a few years, once the country in 1951, and by the 1970s rabies had been rabies has been diagnosed in foxes. diagnosed in all parts of the country. The disease con- This failure to eliminate rabies can almost certainly tinues to be an intractable problem in many regions be explained by the adaptability of red fox popu- today. lations. Foxes are ubiquitous in Europe with an esti- As in the rest of central Europe, the red fox, Vulpes mated density range of 0.1-4.0 foxes per km2 (spring- vulpes, is both the reservoir of rabies infection and the time population) and are thought to be more numer- major vector species (23, 24). A knowledge of certain ous in mixed mosaic habitats than in homogeneous aspects of fox biology is central to an understanding ones (10-12). Difficulties arise in describing the of rabies epidemiology, in particular, the variations in habitat requirements and preferences of foxes fox habitat, population density, population turnover, because these are so broad (the animals being able to and behaviour. survive under the most diverse conditions), and also Rabies occurrence is strongly dependent on fox because fox-hunting and other control measures can density, but the relationship is nonlinear (1, 14, 20), disturb their behaviour. and, according to conventional theory, the frequency Foxes become sexually mature at the end of the first of rabies is also related to fox population turnover year of life and mature females can produce an and fox-to-fox contact rate (1, 2). Rabies cannot average of 4-5 cubs per year (12, 23). A fox popu- persist in areas of very low fox density and low fox-to- lation, reduced by hunting, control measures, rabies, fox contact rate. The threshold population level for or a combination of these, is capable of rapid continued transmission is thought to lie around 0.3 recovery and may even overshoot the original popu- foxes per km2 (15). lation level within 3-7 years (3, 16). The time required The aim of rabies control in central Europe is to to regain the original population level, or at least that reduce fox density to below the threshold level. The required for rabies propagation, depends on the pro- methods currently in use include intensified fox- portion by which the population has been reduced * From the WHO Collaborating Centre for Rabies Surveillance (3). Rabies alone can cause a reduction in the fox and Research, Federal Research Institute for Animal Virus Diseases, of 5007o or more Postfach 1149, D7400 Tubingen, Federal Republic of Germany. population (3, 19). Requests for reprints should be addressed to Dr Schneider. The present paper discusses the rabies statistics for Assistant. the Federal Republic of Germany from 1950 to 1981 2 Head. at the level of Landkreise (administrative units). It 4383 -99- 100 H. C. JACKSON & L. G. SCHNEIDER thus covers a large area over a long period of time. sidered only an indicator of the incidence of the Although the report is necessarily descriptive, it disease. attempts to put the problem in perspective by showing the relative degree to which different areas are Landscape characteristics affected, how the patterns of rabies occurrence vary In order to obtain a preliminary approximation of from region to region and, finally, how landscape the landscape character in regions of the Federal characteristics are associated with the different Republic of Germany with distinct patterns of rabies patterns of occurrence. These epidemiological pat- occurrence, the percentage of different types of land terns of rabies are interpreted in terms of fox popu- use and an indication of the altitude were obtained lation density and contact rate. using 1:2 500 000 maps from the Times World Atlas The many factors that can play a role in fox rabies (21) and the World Atlas ofAgriculture (26). epidemiology (such as geographic variation in fox behaviour, fox population density and population dynamics, type and degree of hunting, and type and RESULTS timing of fox population control methods) are not discussed. Mean rabiesfrequency The mean frequency of reported rabies cases in METHODS each Kreis, calculated from the year rabies was first reported, ranged from 0.0 to 9.0 cases per 100 km2 Rabies occurrence per year. The overall mean frequency for the country was 1.9 cases per 100 km2 per year (standard devi- Data on rabies for 1950-78 were extracted from the ation, 1.5). Tierseuchenbericht (record of notifiable animal dis- Fig. 1 shows the geographic distribution of low, eases) (22), and for 1979-81 from computer records intermediate and high mean rabies frequencies. held at the WHO Collaborating Centre for Rabies Kreise with a mean frequency of fewer than 1.0 Surveillance and Research in Tubingen. The country reported case per 100 km2 per year are found in west was divided into 257 units representing either one or Schleswig-Holstein, north and west Niedersachsen, several Kreise. Because of the large number of Kreis north and west Nordrhein-Westfalen, on the west boundary reforms since 1950 and because the exact bank of the river Rhine in Rheinland-Pfalz, and parts location of rabies cases is not known, rabies cases of north central Bayern and south-east Bayern. Kreise occurring before the Kreis reforms were allocated with a mean rabies frequency of 3.1 cases or more per proportionately to the appropriate present day Kreis. 100 km2 are found in eastern Nordrhein-Westfalen, The size of the Kreis unit ranged from 183 km2 to west Hessen, south Baden-Wurttemberg, and south 2860 km2 (mean, 1013 km2; standard deviation, Bayern. All other Kreise have an intermediate mean 446 kM2); the total area of the Federal Republic of frequency of 1.1-3.0 cases per 100 km2 per year. Germany is 248 144 km2. In terms of the relative importance of rabies, the south of the country plays the major role. The five Animal species southern Lander, Hessen, Rheinland-Pfalz, Saar- Species of animals diagnosed as rabid were not land, Baden-Wurttemberg and Bayern, cover 600o of named with any consistency in the Tierseuchenbericht the area of the Federal Republic of Germany but in until the second half of 1954 and the number of cases 1977-81, for example, they reported 79.3-88.30o of in unspecified species remained high for a number of all cases. years after this. For this reason total rabies cases are discussed rather than cases in foxes alone. The cases Epidemiological patterns of rabies in foxes usually accounted for 60-80% of the total The variation with time in the reported number of diagnosed cases. rabies cases per 100 km2 was plotted for each Kreis. Diagnosed cases in foxes have been estimated to Four distinct epidemiological patterns of rabies (first represent only 2-10O7o of the actual number (4). a Thus described by Jackson (7)) were identified: insignifi- the numbers of officially registered rabies cases, cant occurrence, low undulations, intermittent peaks, which furnish the data base of this study, can be con-- and high oscillations. Kreise with 15 years or less of rabies infection were difficult to classify, particularly a WACHENDORFER, G. The problem of rabies in the European those in south-east Bayern. region. WHO Conference on Surveillance and Control of Rabies, Frankfurt, 15-19 November 1977 (WHO unpublished document, Fig. 2 shows the geographical distribution of the ICP/VPH 001/6). four patterns of rabies occurrence in the Federal RABIES IN THE FEDERAL REPUBLIC OF GERMANY 101 Fig. 2. Geographic distribution of the four epidemio- Fig. 1. Geographic distribution of low, intermediate and logical patterns of rabies in the Federal Republic of high mean rabies frequencies: low mean frequency (light Germany: 1 - insignificant occurrence; 2- low undula- area), 0.01-1.0 cases per 100 km2 per year; inter- tions; 3- intermittent peaks; 4- high oscillations. mediate mean frequency (medium area), 1.-1-3.0 cases Areas with characteristics of more than one pattern are per 100 km2 per year; high mean frequency (dark area), shown, for example, as 42 or 12 where the subscript 3.1 or more cases per 100 km2 per year.