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- Defining classical BSE
- Transmission of classical BSE
- Clinical signs of classical BSE
- Diagnosis of classical BSE
- Classical BSE in Canada
- Ways that Canada protects humans and cattle from BSE
- Additional information
Defining classical BSE
Classical BSE is a disease that affects the nervous system of cattle and is always fatal, progressive and does not respond to treatment. It belongs to a group of diseases that affect the nervous system of humans and other animals called transmissible spongiform encephalopathies. There is no treatment or vaccine available for the disease.
Both atypical BSE and classical BSE are associated with the presence of an abnormal form of a cell protein called "prion" protein that accumulates in and damages the central nervous system of cattle. However, the biological properties and biochemical characteristics of the prion proteins that cause atypical and classical BSE are different.
Classical BSE was responsible for the BSE epidemic that started in the United Kingdom in 1986. All the evidence indicates that the epidemic was caused by feeding cattle with rendered cattle-derived protein meals, and that as long as this practice remains avoided, another epidemic of BSE will not occur. The effectiveness of the prohibition to feed ruminants with ruminants in preventing BSE is evidenced by a rapid and sustained global decline in the number of cases of classical BSE since 2001. It was 2017 the first year with no cases of classical BSE reported world-wide. Since then, only 2 cases have been reported (1 in 2018 and 1 in 2024, both in Scotland)
Classical BSE is assumed to be the cause of variant Creutzfeldt-Jakob disease in people, which was first diagnosed in 1996.
Transmission of classical BSE
Classical BSE can be transmitted to other bovines through the consumption of BSE prion-contaminated feed.
Once a bovine is infected, certain parts of it would contain great amounts of BSE prion infectivity. These are called specified risk materials (SRM).
Livestock industry practices that prevent cattle being exposed to potentially SRM-contaminated feed are crucial. These practices include disposal of dead animals and waste from slaughtered animals, rendering, as well as production, distribution and storage of feed.
Clinical signs of classical BSE
Given that the disease mainly affects the brain of infected cattle, BSE is characterised by its lack of response to treatments and its gradual, very slow onset (the disease may not manifest for up to 7 years in 95% of animals with classical BSE).
Once the animal shows neurological signs of disease, these progress over the course of a few weeks to several months, varying in severity and duration, and ending in death.
Most BSE cases arise as single, isolated animals. The coexistence of multiple animals with behavioural or changes to posture and movements most likely associated with another issue. As none of these signs are limited to BSE, it is expected that individual animals displaying clinical signs suggestive of BSE would be observed in all cattle populations.
Diagnosis of classical BSE
There is no test to diagnose any form of BSE in live animals, although a tentative diagnosis may be made based on clinical signs. Diagnosis can only be confirmed by laboratory examination of the animal's brain after its death.
Further laboratory tests must be performed to distinguish between the classical and atypical BSE, and between the two types of atypical BSE.
Classical BSE in Canada
BSE has been a reportable disease in Canada since 1990. If a case of classical BSE is found, Canada is required to immediately notify the World Organisation for Animal Health (WOAH). Any cases of atypical BSE should be reported once a year.
There have been multiple domestic cases of classical BSE detected in Canada. The first domestic case was reported in 2003 and the latest in 2015, in an animal born in March 2009. All BSE cases were completely destroyed. Check more information on BSE cases.
Ways that Canada protects humans and cattle from BSE
Canada has developed a broad series of measures to manage the risk of BSE in its cattle population:
- import requirements to prevent introduction of commodities that could contain BSE
- legislated feed ban prohibiting feeding ruminants with most mammalian-derived proteins since 1997
- exclusion of SRM from the food supply chain since 2003, with further enhancements implemented in 2007 to also exclude SRM from fertilizers and the entire terrestrial and aquatic animal feed chains
- mandatory reporting of BSE since 1990
- a National BSE Surveillance Program since 1992
Additional information
- Fact sheet – Atypical BSE
- Infographic – Atypical and classical BSE