Bovine Spongiform Encephalopathy (BSE), commonly known as “mad cow disease,” is a severe neurological disorder primarily affecting cattle. It gained international attention after its emergence in the United Kingdom in 1986, raising concerns about food safety and its potential link to human health.
Understanding Bovine Spongiform Encephalopathy
BSE is a progressive, fatal neurological disease of cattle, typically affecting animals four to five years old. It causes central nervous system deterioration, leading to various symptoms. Affected cattle may exhibit temperament changes, such as nervousness or aggression. Coordination problems are also common, including difficulty walking, weakness, tremors, and abnormal posture. Animals may also have difficulty rising, eventually progressing to a state where they cannot stand. Additionally, cattle with BSE may experience weight loss, decreased milk production, or loss of body condition despite maintaining their appetite. The term “spongiform” refers to the spongy appearance of brain tissue when examined microscopically, resulting from abnormal protein accumulation.
The Role of Prions
BSE is caused by an abnormal protein called a prion, a misfolded version of a normal protein found in mammal cells. These misfolded prions induce normal prion proteins to also misfold, leading to an accumulation of abnormal proteins in the brain. This accumulation causes progressive brain damage and the neurological symptoms. Unlike viruses or bacteria, prions do not contain genetic material and are highly resistant to conventional sterilization methods.
The primary way classical BSE spread among cattle was through contaminated feed. The disease propagated by feeding cattle meat-and-bone meal (MBM) containing processed animal products from BSE-infected animals. This allowed infectious prions to enter the food chain and transmit the disease. Ingestion of contaminated feed was the predominant route for the widespread outbreak.
Human Health Concerns
A variant form of Creutzfeldt-Jakob Disease (vCJD) in humans is strongly linked to consuming beef products from cattle infected with classical BSE. This connection, identified in 1996, highlights the disease’s zoonotic nature. The incubation period for vCJD can be lengthy, making it challenging to pinpoint the exact time of exposure.
Initial vCJD symptoms often involve psychiatric issues and persistent painful sensory symptoms. As the disease progresses, individuals typically develop neurological impairments, including poor coordination, involuntary movements, and dementia. Unlike classical CJD, which usually affects older individuals, vCJD tends to affect younger people. Transmission to humans occurs through consuming specified risk materials (SRMs), tissues most likely to harbor prions, such as the brain and spinal cord of infected cattle.
Global Prevention and Surveillance Efforts
Following BSE outbreaks, extensive global measures were implemented to prevent further spread and protect public health. A significant intervention was feed bans, prohibiting mammalian protein in ruminant feed. This addresses the primary route of BSE transmission by preventing the recycling of potentially infected animal products into the feed chain.
Another preventative step involves removing Specified Risk Materials (SRMs) from carcasses destined for human consumption. These materials, including the brain, spinal cord, tonsils, and distal ileum, are most likely to contain prions and are removed during slaughter and processing. Robust surveillance programs also detect BSE cases early, testing animals to ensure prompt identification and containment. Regulations on the movement of live animals and animal products further contribute to controlling the disease by limiting the potential for infected animals or contaminated materials to cross borders.