[Prions--a challenge of Hygieia]. / Prionen--eine Herausforderung der Hygieia.

The history of Prion diseases goes further back than it appears at first sight. The first description was published in 1732. But not before the late 70s and early 80s of the last century the true nature of Scrapie in sheep was recognised. Only the huge outbreak of the bovine spongioforme encephalopathy (BSE) led to more detailed knowledge regarding the transmission of the new type of a pathogen agent.

Diagnostic reliability of clinical signs in cows with suspected bovine spongiform encephalopathy.

The clinical findings in 50 cows with suspected and subsequently confirmed bovine spongiform encephalopathy (BSE) (group A) were compared with the clinical signs in 22 cows with suspected BSE, but with no histological evidence of the disease (group B). The chi-square test for association was used to compare the frequencies with which diagnostic signs or combinations of signs, were positive in the cows of groups A and B. When the frequency of a sign differed significantly, its sensitivity, specificity, efficiency and positive and negative predictive values were calculated. With respect to changes in behaviour the cows in group A more frequently showed increased excitability, nervous ear and eye movements, increased salivation and increased licking of the muzzle than the cows of group B. With respect to changes in sensitivity the cows in group A were more frequently hypersensitive to touch, noise and light than the cows of group B. With respect to changes in locomotion the cows in group A were more frequently ataxic than the cows in group B.

[Frequency of neurologic diseases in cattle]. / Häufigkeit neurologischer Erkrankungen beim Rind.

The cases of neurological diseases at the Institute of Animal Neurology, University of Berne, from 1985-1994 were assessed. During this period 532 cattle with neurological symptoms were examined. After 1980 differential diagnostic investigation of rabies negative brains were not pursued anymore and the number of examined cattle brains had declined to 25-30 per year. With the occurrence of bovine spongiform encephalopathy (BSE) in 1990 in Switzerland the number of cattle brains examined has increased to 75-80 yearly. The most frequently diagnosed neurological diseases found are BSE, followed by listeriosis and viral encephalitides.

[Risk assessment for importing bovine spongiform encephalopathy (BSE)]. / Risikoeinschätzung für die Einschleppung von BSE.

Since the occurrence of bovine spongiform encephalopathy (BSE) in Switzerland in 1990, extensive epidemiological investigations and risk factor analyses were carried out. In this study, statistical data on meat and bone meal traded from 1985 to 1989 were analysed addressing the following questions: i) what amount of meat and bone meal was exported from Great Britain (GB) and where to and ii) what amount of meat and bone meal was imported into Switzerland and where from? The findings led to the hypothesis that imported material potentially infected with scrapie-like agents was the cause for BSE in Switzerland.

[Rabies Tissue Culture Infection Test as an Alternative for the Mouse Inoculation Test]

Rabies has disappeared from large parts of Switzerland. Due to systematic oral fox-vaccination campaings that started in 1987, cases of rabies in wild and domestic animals have been confined to the western frontier with France in the last three years. Nevertheless, some cases of severe exposition of man by rabid or rabies-suspect animals still occur. Rabies can be diagnosed in brain smears of infected animals with high specificity and sensitivity by a direct immunofluorescence method. According to WHO recommendations, negative results are to be confirmed in cases of a human exposition by intracerebral inoculation of brain suspensions in three-weeks-old mice. This method has an excellent sensitivity and is able to detect false-negative results in immunofluorescence, which occur in a very small percentage (0.043%). The disadvantage of this confirmatory assay is the sacrification of relatively high numbers of mice (in the Swiss rabies center about 1,300 animals each year), and the long time required for a final diagnosis: 7-20 days in positive, 21 days in negative cases. The cultivation of virus from brain suspensions on a mouse neuroblastoma cell line is a tempting alternative to the mouse inoculation test. This method usually provides a conclusive diagnosis within a few days. However, in our hands it showed in preliminary experiments an unsatisfactory sensitivity (80.7%). The necessity to carry out strict reproducibility controls in this assay has to be emphasized. Further work must be invested in the improvement of the rabies tissue culture infection test and a careful long-term comparison with the mouse inoculation test will be necessary before the mouse inoculation test can be replaced.