Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland

In sum 16 TSE cases were identified in small ruminants in Switzerland since 1981, of which eight were atypical and six were classical scrapie. In two animals retrospective analysis did not allow any further classification due to the lack of appropriate tissue samples. We found no evidence for an infection with the BSE agent in the cases under investigation. In none of the affected flocks, secondary cases were identified. A Bayesian prevalence calculation resulted in most likely estimates of one case of BSE, five cases of classical scrapie and 21 cases of atypical scrapie per 100'000 small ruminants. According to our models none of the TSEs is considered to cause a broader epidemic in Switzerland. In a closed population, they are rather expected to fade out in the next decades or, in case of a sporadic origin, may remain at a very low level.In summary, these data indicate that despite a significant epidemic of BSE in cattle, there is no evidence that BSE established in the small ruminant population in Switzerland. Classical and atypical scrapie both occur at a very low level and are not expected to escalate into an epidemic. In this situation the extent of TSE surveillance in small ruminants requires reevaluation based on cost-benefit analysis.Transmissible spongiform encephalopathies, in sheep and goats (small ruminants) include classical and atypical scrapie as well as BSE [1]. Common denominators of TSEs are the lethal neurodegenerative alteration of the CNS that involves spongiform lesions, neuronal loss, gliosis and the accumulation of a conformational abnormal isoform (PrPd) of the physiological prion protein (PrPc) [2]. The classical type of scrapie has been a threat in the European sheep livestock for centuries, its first records dating back to the 18th century [3]. Classical scrapie is a contagious disease, infectivity was detected in the CNS, lymphatic tissues, several organs and body fluids of affected animals and its transmission occurs vertically as well