Detection and Control of Prion Diseases in Food Animals

Transmissible spongiform encephalopathies (TSEs), or prion diseases, represent a unique form of infectious disease based on misfolding of a self-protein (PrPC) into a pathological, infectious conformation (PrPSc). Prion diseases of food animals gained notoriety during the bovine spongiform encephalopathy (BSE) outbreak of the 1980s. In particular, disease transmission to humans, to the generation of a fatal, untreatable disease, elevated the perspective on livestock prion diseases from food production to food safety. While the immediate threat posed by BSE has been successfully addressed through surveillance and improved management practices, another prion disease is rapidly spreading. Chronic wasting disease (CWD), a prion disease of cervids, has been confirmed in wild and captive populations with devastating impact on the farmed cervid industries. Furthermore, the unabated spread of this disease through wild populations threatens a natural resource that is a source of considerable economic benefit and national pride. In a worst-case scenario, CWD may represent a zoonotic threat either through direct transmission via consumption of infected cervids or through a secondary food animal, such as cattle. This has energized efforts to understand prion diseases as well as to develop tools for disease detection, prevention, and management. Progress in each of these areas is discussed. 1. Introduction Traditionally infectious diseases were limited to the categories of bacterial, viral, fungal, and parasitic. Despite their differences, these agents are all unified by the requirement of genetic material for protein expression and replication of the agent. More recently, however, a novel infectious disease, which appeared to lack its own genome and is capable of causing devastating pathology in humans and animals, was identified. The causative agent of these diseases has been termed a proteinaceous infectious agent or “prion.” Eventually, after much resistance from the scientific community, it was established that a new class of infectious disease had been discovered. 2. History While descriptions of prion diseases in sheep can be traced back hundreds of years, many of the pivotal experiments which defined the unique nature of the prion diseases did not occur until the 1950s. Specifically, many of the pivotal discoveries of prion diseases reflected efforts of anthropologists, pathologists, and physicians in Papua New Guinea where a novel form of neurological disease called kuru was described. Initially attributed to a “slow virus,” further research in the 1970s