Bovine Spongiform Encephalopathy (BSE), commonly known as mad cow disease, is a progressive, fatal neurological disorder that affects cattle. Because the infectious agent can be transmitted to humans through the consumption of contaminated beef products, BSE represents a significant public health concern. The United States has implemented a comprehensive system of safeguards to minimize the risk of this disease, successfully maintaining a very low incidence within the national herd.
Understanding Prion Diseases
BSE is categorized as a transmissible spongiform encephalopathy (TSE), a group of diseases caused by an infectious agent known as a prion. A prion is a misfolded form of a normal protein (PrP) found in the central nervous system. This misfolded protein acts as a template, forcing normal proteins to assume the abnormal shape, causing them to accumulate in the brain.
This accumulation forms deposits, leading to the characteristic “spongy” appearance of the tissue and neurological damage. Prions are highly resistant to conventional sterilization methods, such as heat, radiation, and common disinfectants. Specialized, high-intensity processes are required to eliminate them from potentially contaminated materials.
The History and Status in the United States
The first case of BSE identified in the United States occurred in December 2003, in a dairy cow imported from Canada. This initial case was classified as classical BSE, the form associated with contaminated feed. Since 2003, the total number of confirmed BSE cases has remained extremely low, with only seven cases identified through 2023.
The 2003 detection was the only instance of classical BSE. The remaining six cases were classified as atypical BSE, a form that arises spontaneously in older cattle (usually eight years or older) and is not linked to contaminated feed. Due to the low incidence and robust control measures, the World Organisation for Animal Health (OIE) upgraded the United States’ status to “negligible risk” for BSE in 2013. This designation is the lowest risk classification possible and reflects confidence in the country’s surveillance and prevention systems.
Regulatory Measures Protecting the Food Supply
The U.S. Department of Agriculture (USDA) and the Food and Drug Administration (FDA) manage a multi-layered system of safeguards to protect the food supply from BSE.
Feed Ban
The primary measure is the strict ban on feeding most mammalian protein to cattle and other ruminants, implemented by the FDA in 1997. This measure breaks the primary transmission route of classical BSE by preventing the use of rendered cattle remains in cattle feed, which caused the widespread outbreak in the United Kingdom.
Specified Risk Material (SRM) Removal
Mandatory removal of Specified Risk Materials (SRMs) occurs at the time of slaughter. SRMs are the parts of the animal most likely to harbor prions. These high-risk tissues are declared inedible and prohibited from entering the human food supply or animal feed. SRMs include:
- The brain, skull, spinal cord, and vertebral column from cattle 30 months of age and older.
- The distal ileum (a part of the small intestine) from cattle of all ages.
Surveillance
The USDA maintains a targeted surveillance program that tests cattle exhibiting neurological signs or those that are non-ambulatory at slaughter. This provides continuous verification that control measures are working effectively. The combination of the feed ban, SRM removal, and surveillance minimizes the risk of BSE transmission through the food supply.
The Human Health Component
The human equivalent of classical BSE is Variant Creutzfeldt-Jakob Disease (vCJD), contracted by consuming contaminated beef products. The disease has a long incubation period, often lasting a decade or more before symptoms manifest. Initial signs often involve psychiatric symptoms, such as depression and anxiety, followed later by neurological issues like poor coordination and dementia.
Once symptoms appear, most patients succumb to the illness within 13 to 14 months. Worldwide, only 233 cases of vCJD have been reported since 1996, with the majority occurring in the United Kingdom. Only four cases have ever been reported in the United States, and evidence suggests all individuals contracted the disease outside of the country years or decades prior.