Mad cow disease, or bovine spongiform encephalopathy (BSE), is a neurodegenerative condition primarily affecting the central nervous system of cattle, leading to lesions that give brain tissue a sponge-like appearance. Known for its transmission via prions (infectious proteins), BSE has two forms: the classic type, spread through the consumption of contaminated food, and the atypical type, which appears spontaneously in older animals. In Brazil, this disease is of significant importance, not only to public health but also to food safety, requiring constant monitoring from authorities and rural producers alike.
BSE caused a global health crisis, particularly in Europe, during the 1980s and 1990s, affecting markets and leading to strict health regulations worldwide. Today, Brazil is considered a country with an insignificant risk for the disease, yet vigilance remains high to prevent outbreaks and protect the human population from a variant of BSE, known as variant Creutzfeldt-Jakob disease (vCJD), which can affect people.
What is bovine spongiform encephalopathy (BSE)?
Bovine spongiform encephalopathy is a fatal disease with no cure or effective treatment, caused by prions in the central nervous system of cattle. Prions are infectious proteins that accumulate in the animal’s brain, progressively degenerating brain tissue and leading to lesions that give it a spongy appearance. BSE is highly debilitating, presenting a range of neurological and behavioral symptoms in affected animals.
The disease has two main variants: the classic form, which occurs due to the ingestion of prion-contaminated food, and the atypical form, which appears spontaneously in older cattle, unrelated to their diet. In Brazil, the ban on the use of animal-based proteins in ruminant feed since 1996 has been crucial in preventing the classic form, considered the more dangerous of the two.
Symptoms and progression of mad cow disease
BSE’s clinical presentation in cattle is characterized by symptoms that develop and progress over weeks or months. Initial symptoms include behavioral changes, such as nervousness and aggression. Over time, cattle show heightened sensitivity to stimuli like sound, light, and touch, leading to extreme reactions when interacting with other animals or humans.
Another critical symptom of BSE is mobility issues. As the disease advances, affected cattle display a staggering walk, loss of motor coordination, and, eventually, immobility. Other common signs include weight loss, reduced milk production, muscle tremors, and involuntary movements. Due to the diverse range of symptoms, BSE can easily be mistaken for other neurological conditions, such as rabies or poisoning.
Modes of transmission for mad cow disease
Classic BSE, also known as the infectious form, is transmitted through the consumption of prion-contaminated foods, like meat and bone meal containing ruminant proteins. For this reason, regulating cattle feed is one of the primary measures to prevent the disease from spreading. In Brazil, the ban on the use of ruminant-derived byproducts in ruminant feed was decisive and remains a cornerstone of the country’s sanitary safety.
The atypical form of BSE, in contrast, appears spontaneously in older animals and is not linked to diet. The origin of this form is still not fully understood, but it is believed to be a spontaneous mutation of normal proteins that transform into prions. Though rare and sporadic, the atypical form still requires monitoring.
Main prevention and control measures in Brazil
To prevent mad cow disease, Brazil has implemented several preventative and control measures. Key guidelines for protecting the national herds and the population include:
- Strict monitoring of cattle feed to prohibit the use of meat and bone meals from ruminants.
- Continuous surveillance, with herd monitoring, especially in cattle over 30 months old.
- Immediate reporting protocols to sanitary authorities in suspected cases.
- Slaughter of diagnosed animals to prevent potential disease spread.
- Education campaigns to raise awareness among ranchers about the disease’s symptoms and risks.
- Ongoing updates to disease control policies and programs, following recommendations from the World Organisation for Animal Health (WOAH).
- Rigorous enforcement to ensure all animal feeding regulations are followed.
Challenges in diagnosing and treating BSE
The definitive diagnosis of BSE can only be made through laboratory tests detecting prions in cattle brain tissue, usually after the animal’s death. In suspected cases, a detailed examination of the central nervous system reveals the characteristic lesions, confirming the diagnosis. However, the lack of effective methods to diagnose BSE in live animals complicates early identification, especially in large herds.
Since there is no treatment for BSE, animals exhibiting symptoms or identified as carriers must be culled to prevent contamination of the herd. This measure, although severe, is essential for disease control and ensures it does not enter the human food chain.
BSE in Brazil and international recognition
Since 2012, Brazil has been classified by the WOAH as a country with an insignificant risk for BSE, a designation that reflects the country’s efforts to implement strict control policies. This classification is essential for Brazil’s livestock sector, as it reinforces international confidence in Brazilian beef, facilitating exports and ensuring product quality for local and foreign consumers.
In September 2024, Brazil introduced updated guidelines for the National Bovine Spongiform Encephalopathy Program (PNEEB) to align domestic practices with international standards and maintain its low-risk status. These measures protect public health and strengthen Brazil’s position in the global beef market.
Health risks of BSE to humans
BSE is considered a zoonotic disease, as it is linked to a similar disease in humans called variant Creutzfeldt-Jakob disease (vCJD). Transmission to humans occurs primarily through the consumption of contaminated meat, especially brain and spinal cord tissue, where prion concentration is highest. vCJD is a rare and fatal condition that progressively degenerates the central nervous system, leading to death within months of symptom onset.
Fortunately, Brazil has not recorded any cases of vCJD in humans, highlighting the effectiveness of its control and food safety measures. However, ongoing vigilance is necessary to avoid any transmission risk and protect public health.
Economic and health impact of BSE on livestock
The presence of BSE cases can have a significant economic impact on the livestock industry, directly affecting consumer confidence and beef exports. During outbreaks of the disease in Europe, demand for beef drastically dropped, resulting in financial losses and the adoption of strict health policies. Today, with surveillance measures in place and international recognition, Brazil maintains a stable and safe market but continues to monitor herds to prevent any risk that could affect both the economy and public health.
Maintaining these control practices is vital for Brazil, given the importance of livestock to the country’s economy. Mad cow disease not only poses a risk to animal and human health but can also harm the reputation of the beef industry, with long-term consequences.
Steps for food safety and animal health
To ensure food safety and herd health, Brazil adopts a preventative approach with strict policies and educational programs for ranchers. Animal feed monitoring, laboratory testing, and commitment to WOAH guidelines form the foundation of the national strategy against BSE. Awareness and cooperation from producers and authorities are crucial to upholding Brazil’s health status and protecting the population from the disease.
