What is 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. No cases of classical BSE had been reported world-wide in 2017, 2019 and 2020.
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 stock 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 signs of disease, these progress over the course of a few weeks to several months, varying in severity and duration, and ending in death. Signs can include:
- Progressive behavioural changes such as increased excitability, depression, nervousness, excessive and asymmetrical ear and eye movements, apparent increased salivation, increased licking of the muzzle, teeth grinding, hypersensitivity to touch and/or sound (hyperaesthesia), tremors, excessive vocalisation, panic-stricken response and excessive alertness.
- Changes to posture and movements, such as abnormal posture (dog sitting), abnormal gait, low carriage of the head, head shyness, difficulty avoiding obstacles and inability to stand.
- Generalised non-specific signs, such as reduced milk yield, loss of body condition, weight loss, and bradycardia and other disturbances of the cardiac rhythm.
The vast majority of BSE cases arise as single, isolated animals. The concurrence 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
There have been 17 indigenous cases of classical BSE detected in Canada. Of these, one was born in 1996, 15 were born after the 1997 feed ban, and one was born after the 2007 enhanced feed ban. The first indigenous case was reported in 2003 and the latest one in 2015, in an animal born on March 2009. All BSE cases were completely destroyed.
How does Canada protect humans and cattle from BSE
Canada has put in place a comprehensive series of measures to manage the risk of BSE in its cattle population. There are import requirements to prevent introduction of commodities that could contain BSE, and legislation prohibiting feeding ruminants with most mammalian-derived proteins has been in force since 1997. Exclusion of SRM from the food supply chain started in 2003, and further enhancements were implemented in 2007 to also exclude SRM from fertilizers, and the entire terrestrial and aquatic animal feed chains. BSE has been a reportable disease in Canada since 1990, and BSE surveillance started in 1992.
Follow these links for more information:
- BSE import policy for bovine animals and their products and by-products
- Enhanced Animal Health Protection from BSE – SRM
- BSE enhanced surveillance program
Canada is required to notify the World Organisation for Animal Health (WOAH; founded as Office International des Épizooties (OIE)) of any occurrence of a confirmed BSE case (either classical or atypical).