Overview

Bovine spongiform encephalopathy (BSE), widely known as mad cow disease, is a progressive, fatal disorder of the central nervous system in cattle. It belongs to the group of transmissible spongiform encephalopathies (TSEs), which are caused by abnormal forms of a prion protein. Unlike conventional infectious agents, these misfolded proteins carry disease without nucleic acids and cause characteristic sponge-like degeneration of brain tissue.

Symptoms and pathology

Infected animals develop subtle changes at first and then more obvious neurological and behavioral signs. Pathological hallmarks include vacuolation ("holes") in gray matter, neuronal loss and gliosis. Clinical features in cattle commonly include:

  • Behavioral changes: nervousness, apprehension or aggression
  • Coordination problems: ataxia, difficulty rising and abnormal gait
  • Loss of condition despite continued appetite, reduced milk yield
  • Sensory abnormalities and hypersensitivity to stimuli

Definitive diagnosis historically relies on postmortem examination of brain tissue with histology and biochemical tests that detect the protease-resistant prion isoform.

Transmission and incubation

BSE is primarily associated with exposure of cattle to feed contaminated with infected ruminant tissue; recycling of animal protein in feed amplified the epidemic. The disease has a long incubation period, typically measured in years rather than weeks, so animals may appear healthy while harbouring disease. Species barriers affect transmission efficiency, but consumption of BSE-contaminated beef products has been linked to a human form of the disease known as variant Creutzfeldt–Jakob disease (vCJD).

History and impact

Large-scale BSE outbreaks were identified in the United Kingdom and other countries in the 1980s and 1990s. In the mid-1990s public health authorities signalled that BSE could be transmitted to humans; a high-profile announcement by the UK government in 1996 heightened public concern and led to major policy changes. The epidemic caused severe disruption of the cattle industry: over 179,000 infected cattle were recorded in the worst-affected nation and approximately 4.4 million animals were culled in control efforts, triggering trade restrictions and lasting economic effects.

Control, prevention and public health measures

Control strategies reduced risk and include bans on feeding ruminant-derived protein to cattle, removal of specified risk material (high-risk tissues such as brain and spinal cord) from the food chain, targeted surveillance and testing, strict slaughterhouse controls and culling of confirmed cases. These measures, together with improved surveillance, have greatly reduced the incidence of classical BSE.

BSE is one member of the wider family of prion diseases, which also includes scrapie in sheep and chronic wasting disease in cervids. Human prion diseases such as sporadic CJD differ in cause and epidemiology from vCJD, which is associated with BSE exposure. There is no cure for prion diseases: research focuses on diagnostics, understanding prion propagation and preventing exposure. Public-health responses and feed regulations have been central to preventing recurrence of large epidemics.

For further technical background and summaries of regulatory changes, see official guidance and reviews by health agencies and veterinary authorities (historical public health announcement).