Mad cow disease

Mad Cow Disease, scientifically known as Bovine Spongiform Encephalopathy (BSE), is a neurodegenerative disease that affects cattle, causing progressive deterioration of the brain and nervous system. The disease belongs to a group of fatal conditions known as transmissible spongiform encephalopathies (TSEs), which occur in both animals and humans. It gained global attention during the 1990s after an outbreak in the United Kingdom, which led to significant public health concerns due to its link with a human variant known as variant Creutzfeldt–Jakob disease (vCJD).

Nature and characteristics of the disease

Mad Cow Disease is caused not by bacteria, viruses, or fungi, but by prions — misfolded forms of a normal protein found in the brain. These abnormal prions (PrP^Sc) induce other normal proteins (PrP^C) to misfold, triggering a chain reaction that results in brain damage. The affected brain tissue develops sponge-like holes, giving the disease its name “spongiform encephalopathy.”
Key characteristics include:

• Long incubation period: Symptoms may take years to appear after infection.
• Irreversible progression: Once clinical signs appear, the disease advances rapidly and is always fatal.
• No known cure or treatment: There is currently no way to halt or reverse prion-induced brain degeneration.

Symptoms in cattle

The symptoms of BSE usually appear in adult cattle aged between four and six years. They include:

• Changes in temperament or behaviour (nervousness, aggression, anxiety).
• Difficulty in movement and loss of coordination.
• Decreased milk production.
• Weight loss despite normal appetite.
• Hypersensitivity to touch or sound.

As the disease progresses, affected cattle may collapse, lose the ability to stand, and eventually die.

Transmission and causes

BSE is primarily transmitted through the consumption of feed containing contaminated animal products, particularly meat and bone meal (MBM) derived from infected cattle or sheep. During the 1980s and early 1990s, animal by-products were commonly used as protein supplements in livestock feed. When prion-contaminated tissues — such as brain and spinal cord material — entered the feed supply, the disease spread rapidly among cattle.
The disease does not spread through direct contact between animals. However, because prions are highly resistant to heat, disinfectants, and radiation, they can persist in the environment and remain infectious for long periods.

Human infection: Variant Creutzfeldt–Jakob Disease (vCJD)

The human form associated with BSE, variant Creutzfeldt–Jakob disease (vCJD), is a rare but fatal brain disorder. It is believed to result from consumption of beef or beef products contaminated with BSE prions.
Symptoms of vCJD include:

• Psychiatric changes such as depression, anxiety, or personality alterations.
• Loss of coordination, balance, and motor control.
• Progressive dementia and memory loss.
• Involuntary movements and difficulty speaking or swallowing.

The disease progresses rapidly once symptoms develop, usually leading to death within a year.

Discovery and history

Bovine Spongiform Encephalopathy was first identified in 1986 in the United Kingdom, following observations of unusual neurological symptoms in cattle. By the early 1990s, the disease had spread widely within the UK herd and to several other countries through cattle exports and contaminated feed.
The BSE crisis peaked between 1992 and 1993, with over 35,000 confirmed cases in the UK in a single year. In 1996, the British government officially linked BSE to the emergence of variant CJD in humans, prompting global alarm and sweeping changes in food safety regulation.

Global response and control measures

Governments and international health agencies implemented extensive measures to control and prevent the spread of BSE, including:

• Feed bans: Prohibiting the use of animal-derived protein in livestock feed (especially ruminant feed).
• Culling of infected and at-risk animals: Millions of cattle were slaughtered in the UK and Europe to prevent further transmission.
• Surveillance and testing programmes: Routine monitoring of cattle, especially those displaying neurological symptoms.
• Traceability systems: Implementing identification and tracking of livestock to trace the origin of meat products.
• Public education and export restrictions: Measures to reassure consumers and limit international spread.

The World Organisation for Animal Health (WOAH) and the World Health Organization (WHO) continue to provide guidelines for surveillance, control, and food safety related to prion diseases.

Economic and social impact

The BSE outbreak had profound economic consequences, particularly in the agricultural and food industries:

• Loss of consumer confidence led to sharp declines in beef sales.
• Trade bans were imposed on British beef exports by many countries.
• The UK government spent billions of pounds compensating farmers and implementing eradication programmes.
• Public anxiety about food safety spurred major reforms in food regulation and veterinary inspection practices across Europe.

The crisis also influenced global policy on food transparency, traceability, and biosecurity standards.

Scientific understanding of prions

Prions represent a unique form of infectious agent, consisting entirely of misfolded proteins with no nucleic acids. They challenge the traditional understanding of infection and heredity. Nobel laureate Stanley B. Prusiner first proposed the prion theory in the 1980s, which was later confirmed through experimental research on scrapie (a similar disease in sheep) and BSE.
Key properties of prions include:

• Extreme resistance to conventional sterilisation methods.
• Ability to remain infectious in the environment for years.
• Capability of crossing species barriers under certain conditions (as with BSE and vCJD).

Related prion diseases

Mad Cow Disease belongs to the broader family of transmissible spongiform encephalopathies (TSEs), which affect various species:

• Scrapie – affects sheep and goats.
• Chronic wasting disease (CWD) – affects deer, elk, and moose.
• Kuru – a human prion disease historically found among the Fore people of Papua New Guinea.
• Classical Creutzfeldt–Jakob disease (CJD) – occurs spontaneously or through inherited prion mutations in humans.

Each of these diseases shares the hallmark feature of sponge-like degeneration of brain tissue and inevitable fatality.

Current status and prevention

Thanks to strict feed regulations, extensive testing, and control programmes, BSE cases have dramatically declined since the early 2000s. Only sporadic isolated cases occur today, mostly in older cattle, and are usually detected through routine surveillance rather than active outbreaks.
Preventive measures continue to include:

• Prohibition of animal-derived protein in ruminant feed.
• Exclusion of high-risk materials (brain, spinal cord) from the human food chain.
• Continued testing of cattle at slaughterhouses.
• Strict import controls on animals and feed ingredients.

The WHO maintains that beef and dairy products from properly regulated food systems are safe for consumption.

Broader significance

The BSE crisis marked a turning point in global food safety, agricultural regulation, and public health policy. It underscored the need for:

• Transparent communication between governments and consumers.
• Scientific research on novel infectious agents like prions.
• International collaboration in monitoring zoonotic diseases (diseases that can spread from animals to humans).