Bovine spongiform encephalopathy (BSE)--infectious, contagious, zoonotic or production disease?

Abstract

In 1986, a new progressive neurological condition similar to scrapie of sheep and goats was recognised in cattle in the United Kingdom (UK), and was named bovine spongiform encephalopathy (BSE). There is an ongoing discussion whether BSE should be classified as infectious, contagious, or zoonotic, and if it fits the definition of a production disease. The objective of this work is to briefly describe the main characteristics of transmissible spongiform encephalopathies (TSE), to review the epidemiology of BSE, and to address the question of how to classify BSE. TSEs are characterised as chronic wasting diseases with spongiform vacuolation and the accumulation of infectious prion protein (PrP(Sc)) in the central nervous system. TSE infectivity is very difficult to inactivate. Cattle BSE most likely originated from sheep scrapie, although this will remain to be an issue for debate. The disease can be transmitted from cattle to a range of species, and has resulted in smaller TSE epidemics in domestic cats, zoo cats and zoo ruminants, and in humans. Transmission in the field occurred through feed containing ruminant-derived protein, and measures to prevent the recycling of infectivity have proven effective to reduce the number of new infections. Mandatory reporting of clinical suspects combined with targeted screening of risk populations is needed to assess the BSE status of a country. Infection studies and the transmissibility to other species classify BSE as infectious and zoonotic. Absence of excretion of the agent, and therefore of horizontal transmission, categorise BSE as non-contagious. However, BSE is a multifactorial infectious disease that is dependent on management factors (mainly feeding), and therefore fits into the broader definition of production diseases.