Epidemiologische Untersuchungen zum Vorkommen der Tollwut und des kleinen Fuchsbandwurmes, Echinococcus Multilocularis, im Saarland

Abstract

Since its first appearance in 1965, rabies in the state of Saarland subsequently regularly occurred at low frequencies, with an average of three cases per 100 sqkm and year. Different measures to control rabies, especially oral vaccination of foxes which started in 1987 remained unsuccessful. Despite temporally and spatially limited successes, rabies is not eradicated completely in the state until today. In this study an analysis of rabies occurrence in the Saarland was carried out for the years 1986 to 1995, based on official rabies reports. The role of potential contributing factors is considered. The effect of the oral immunization of foxes was investigated, based on infection rates of game animals. Also, rabies occurrence in foxes from August 1994 until August 1995 was analysed and results of follow-up investigations on the immunization control program (serodiagnosis, oxytetracycline detection) were evaluated. Due to the fact that the state Saarland for three decades is considered an endemic area for rabies and because in mid-Europe spatial distributions and regional frequencies of rabies are related to those of infections with Echinococcus multilocularis, the epidemiological situation of this parasite in foxes furtheron was investigated.

From 1986 to 1995 a total of 3317 domestic and game animals were examined for rabies in the Saarland. 1040 animals (31.4%) were found positive for rabies, with 16% of cases occurring in domestic animals and 84% in wildlife animals. Infection rates of foxes (74% of all cases of wildlife rabies) underline the predominant role of this species. Monthly infection rates of domestic and wildlife animals revealed the typical seasonal course of rabies: distinct maxima of incidence rates did occur in spring and autumn whereby the maxima during autumn months on average were higher than those during the spring months. A marked decreasing trend in rabies infection rates in wildlife animals from the North to the South/Southeast was observed. Infection rates of wildlife animals significantly were lowered in municipalities where 20 to 40% and more than 40% of areas were covered by forests and where at the same time both the proportion of agricultural areas decreased and areas used for settlements and traffic increased. In contrast, rabies infection rates were significantly elevated in municipalities where, proportionally, forest coverage was low (< 20% of areas) and where proportions of agricultural areas decreased while areas used for settlements and traffic increased. In total, rates of rabies cases were elevated with decreasing percentages of forests, increasing percentages of agricultural areas and increasing altitudes.

Despite the commencement of oral immunization in 1987, incidence rates of rabies in the Saarland considerably fluctuated during the years 1986 to 1995. With the reservation, that the number of rabies-positives in the total number of wild animals submitted for investigation can only provide an estimate of infection rates in the entire wildlife population, it is nevertheless inferred that the course of rabies in the Saarland between 1986 and 1995 was largely non-influenced by the oral vaccination campaigns during these years. The analysis of results of the diagnostic indicators, accompanying vaccinations, confirms the failure of the vaccination campaign.

On the basis of investigations of foxes submitted between August 1994 and August 1995, the following is concluded:

1. Of the total of 384 examined foxes 237 (61,7%) were confirmed rabies-positive. No sex- and age-dependencies of positive cases could be established. 2. The number of hunted foxes per sqkm and year (Hunting Indicator of Population Density - HIPD) was not directly related to infection rates of foxes. The HIPD appears to be more influenced by temporal and spatial variations in hunting habits and -intensities. 3. The efficacy controls of vaccinations, carried out in spring and autumn 1994 and in spring 1995 revealed a seroconversion rate of 46% and an OTC-rate of 51%. These results suggest that the vaccination campaigns did only insufficiently cover the fox population. 4. From the total of 352 foxes examined for the presence of E. multilocularis, 68 foxes (19,3%) were positive. Prevalences were not age- and sex-dependent. 5. Significantly fewer foxes were infected with E. multilocularis in the summer- than in the winter half-year. 6. The spatial distribution of infection rates with E. multilocularis, with highest rates occurring in the North (Landkreis St. Wendel, Merzig-Wadern) and in the eastern areas (Neunkirchen), was comparable to that of rabies. Also, distributions of both zoonotic diseases, rabies and echinococcosis, did show similarities in regards to the land use of areas, their altitudes and human population densities.