Bovine Spongiform Encephalopathy (BSE), commonly known as Mad Cow Disease, is a progressive and always fatal neurological disease affecting cattle. This condition leads to brain damage and deterioration over time. The disease is caused by an infectious protein, known as a prion, which accumulates in the brain and spinal cord of affected animals.
Understanding Bovine Spongiform Encephalopathy (BSE)
BSE involves abnormal prions, misfolded proteins that cause normal brain proteins to misfold. This accumulation of abnormal prions results in sponge-like holes in the brain tissue, leading to severe neurological symptoms in cattle. Affected animals may exhibit changes in temperament, such as nervousness or aggression. They can also show abnormal posture, incoordination, difficulty walking, weight loss, and decreased milk production despite continued appetite.
The primary way classical BSE spreads among cattle is through contaminated feed. This occurs when feed contains specified risk materials (SRMs) derived from infected animals, such as brain and spinal cord tissue. The Food and Drug Administration (FDA) banned ruminant protein in feed for ruminants in 1997, and certain high-risk cattle tissues in feed for all animals in 2009, to prevent this transmission.
BSE in the United States
The United States has experienced a very low incidence of BSE within its cattle herd. The first case of classical BSE in the U.S. was confirmed by the U.S. Department of Agriculture (USDA) in December 2003, in a cow imported from Canada. This animal was born before feed bans were fully established.
Since this initial case, the U.S. has detected six additional cases, all identified as atypical BSE. Atypical BSE differs from classical BSE as it occurs rarely and spontaneously in older cattle and is not associated with contaminated feed. These atypical cases do not impact a country’s official BSE risk status. The U.S. has maintained a “negligible risk” status for BSE, as recognized by the World Organisation for Animal Health (WOAH, formerly OIE) since 2013, due to effective control measures and low prevalence.
Ensuring Beef Safety
The United States has implemented comprehensive safeguards to prevent BSE from entering the food chain and to protect consumers. A primary measure is the ban on specified risk materials (SRMs) in both animal feed and human food. These SRMs include the brain, spinal cord, and certain other tissues from cattle, as they are most likely to contain the infectious prion. This removal of SRMs from all cattle presented for slaughter is a primary safeguard against BSE.
Robust surveillance programs are also in place, with the USDA testing high-risk cattle for BSE. This involves testing animals that show neurological signs or are deemed unsuitable for slaughter. The Food and Drug Administration (FDA) and the United States Department of Agriculture (USDA) enforce regulations to ensure U.S. beef safety. These efforts include strict import controls on live animals and animal products from countries with BSE risk.
Human Health Implications
The human form of BSE is known as Variant Creutzfeldt-Jakob Disease (vCJD), a rare and fatal brain disease. There is strong epidemiological and laboratory evidence linking vCJD to the consumption of beef products contaminated with central nervous system tissue from BSE-infected cattle. Symptoms of vCJD can include psychiatric issues like depression and anxiety, followed by neurological signs such as poor coordination and dementia.
Worldwide, 233 cases of vCJD have been reported since 1996, with the majority occurring in the United Kingdom. In the United States, four cases of vCJD have been identified. However, all four individuals contracted the disease outside the U.S. The risk to humans from eating U.S. beef is considered negligible due to effective preventative measures and the country’s negligible risk status.