Bovine spongiform encephalopathy
Bovine spongiform encephalopathy (BSE) is a progressive, fatal disease of the nervous system of cattle that is caused by the accumulation of an abnormal protein called ‘prion’ in nervous tissue. Two forms can be distinguished: the classical BSE occurs in cattle after ingesting prion contaminated feed, while the atypical BSE is believed to occur spontaneously in all cattle populations. The classical form was first detected in 1986, and the implementation of appropriate control measures resulted in its decline worldwide. To date, the incidence of both forms is negligible and estimated to approach zero cases per million cattle. BSE is considered zoonotic due to its assumed link with the emergence of variant Creutzfeldt-Jakob disease in humans. BSE is an OIE-listed disease, for which the OIE has established official recognition of sanitary risk status for its classical form.
What is BSE?
BSE is a disease of the nervous system of cattle, which has a long incubation period between two and eight years, and occasionally longer. There is currently no treatment or vaccine against it.
It is one of a group of diseases known as transmissible spongiform encephalopathies (TSE), or prion diseases, characterised by the accumulation in nervous tissue of an abnormal infectious protein called a prion. This group notably includes scrapie in sheep and goats, chronic wasting disease (CWD) in cervids, and variant Creutzfeldt-Jakob disease (vCJD) in humans. A neurological disease in domestic and zoo felids has also been linked to BSE.
The hypothesis that BSE prions have been passed to humans, causing vCJD, is strongly supported by epidemiological and clinicopathological studies.
|Classical versus atypical BSE|
There is a distinction to be made between these two forms, or strains: Classical BSE occurs through the consumption of contaminated feed (see section ‘transmission and spread’). Whilst classical BSE was identified as a significant threat in the 90s, its occurrence has markedly decreased over the past years, as a result of the successful implementation of effective control measures and is now estimated to be extremely low (close to 0 cases). Atypical BSE refers to naturally and sporadically occurring forms, which are believed to occur in all cattle populations at a very low rate, and which have only been identified in older cattle when conducting intensive surveillance.
In the early 2000s, atypical prions causing atypical BSE were identified as the result of enhanced surveillance for transmissible spongiform encephalopathies. The number of cases of atypical BSE is negligible.
Indeed, whilst to date there is no evidence that atypical BSE is transmissible, recycling of the atypical BSE agent has not been ruled out, and therefore measures to manage exposure risk in the feed chain continue to be recommended as a precautionary measure. For more details, see BSE situation in the world.
BSE is an OIE-listed disease and must be reported to the OIE, as indicated in the OIE Terrestrial Animal Health Code. The occurrence of atypical BSE is not considered for the purpose of official BSE risk status recognition as it can spontaneously occur in any cattle population.
Transmission and spread
The clear understanding of the origin and development of the disease in animals is still subject to scientific research. Nevertheless, it has been proven that certain tissues of infected animals, so-called specified risk materials (SRMs), are most likely to contain and therefore transmit the BSE prion. According to the OIE Terrestrial Animal Health Code, these tissues include brain, eyes, spinal cord, skull, vertebral column, tonsils and distal ileum.
Scientists believe that cattle are usually infected through the dietary intake of prion contaminated feed during their first year of life. The risk of contamination occurs if the feed contains products derived from ruminants, such as meat-and-bone meal (MBM), which is the protein product obtained by rendering certain parts of animal carcasses, including those of farmed small ruminants and cattle, that are not used for human consumption.
The infectious prion is resistant to commercial inactivation procedures such as heat, which means that it may not be destroyed in the rendering process. The incidence of BSE was much greater for dairy than beef cattle, since generally, dairy herds are fed concentrate rations that, before the introduction of stricter controls, contained MBM.
Meanwhile, there is no evidence of direct transmission between animals (horizontal transmission) and little data support that BSE is transmitted from mother to offspring (vertical transmission).
Classical BSE was first diagnosed in cattle in the United Kingdom (UK) in 1986, but had probably been present in the country’s cattle population since the 1970s or earlier. It has then been reported in 25 countries other than the UK, mainly in Europe, Asia, the Middle East and North America.
Nowadays, as a result of the successful implementation of effective control measures, the prevalence of classical BSE is extremely low, as well as its global sanitary impact and public health risk.
For more details, see BSE situation in the world.
Public health risk
The likely transmission of BSE to humans, assumed to cause in vCJD, along with the incapability to predict the size of the vCJD epidemic triggered a public health crisis during the 90s. To date, the number of vCJD clinical cases identified is extremely low.
There are compelling indications that vCJD could be acquired through the consumption of contaminated beef products (as defined below), or contact with medical devices contaminated with BSE prions. It is to be noted that dietary exposure to red meat (i.e., deboned skeletal muscle) and milk and milk products is considered safe.
To prevent human and animal infection, and the recycling and amplification of prions, many countries have enforced the systematic removal of tissues that might contain a significant amount of BSE infectivity, named specified risk materials (SRMs), from bovine carcasses. This measure, together with the ban on the use of processed animal proteins in feed (i.e., ruminant-to-ruminant feed ban), have been demonstrated to be strongly efficient in controlling exposure to BSE agents.
The production of human and veterinary pharmaceutical products, and medical devices or cosmetics, should adhere to strict requirements and ideally avoid the use of bovine materials or materials from other animal species in which prion diseases naturally occur.
For more information on vCJD, consult the WHO’s website
The time between the moment an animal gets infected with the BSE agent and the onset of clinical signs is between two to eight years. Therefore clinical signs of BSE are found in adult animals, which may demonstrate some of the following clinical signs:
- nervous or aggressive behaviour;
- hypersensitivity to sound and touch, twitching, tremors;
- abnormal posture;
- lack of coordination and difficulty in rising from a lying position;
- weight loss, or;
- decreased milk production.
The course of disease is usually subacute to chronic, and affected animals display progressive neurological signs.
There is no effective treatment and affected animals will inevitably die if the disease is left to run its course.
BSE may be suspected based on clinical signs.
To date, there is no method that allows to confirm the presence of the BSE agent in live animals.
As indicated in the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, diagnosis can be achieved by histopathology (i.e. microscopic examination) of the medulla oblongata (a portion of the brain). However, histopathology as the primary method would not be appropriate for any of the BSE surveillance streams indicated in the Terrestrial Code. The confirmation of the diagnosis is reached with immunochemical methods including immunohistochemical (IHC) techniques and Western immunoblot.
Prevention and control
In accordance with the OIE Terrestrial Animal Health Code, an effective strategy for preventing the introduction or dealing with occurrences of BSE includes:
- targeted surveillance of occurrences of clinical neurological disease;
- transparency in reporting findings of BSE;
- safeguards on importation of live ruminant species and their products;
- removal of specified risk materials (SRMs) (brain, spinal column, etc.) during slaughter and processing of carcasses and from the human food and the animal feed chains;
- prohibition of the inclusion of SRMs in animal feeds, thus removing potentially contaminated material from the food chain;
- humane destruction of all suspected animals exposed to prion contaminated feed;
- banning the use of MBM in ruminant feed (ruminant-to-ruminant feed ban, further reinforced by a mammalian-to-ruminant feed ban);
- appropriate disposal of carcasses and all animal products; and
- livestock identification to enable effective surveillance and tracing of suspected livestock.
BSE is a disease for which the OIE has established official recognition of sanitary risk status in countries in their entirety or in defined zones and compartments, through a transparent, science-based and impartial procedure.
The categorisation of BSE risk status only applies to classical BSE.
‘Atypical BSE’ forms are excluded from the scope of the categorisation, because they are believed to occur spontaneously in all cattle populations at a very low rate.
The OIE officially recognises two categories of BSE risk status. The current requirements for the recognition and maintenance of these categories can be summarised as follows:
A country, zone or compartment not recognised as having a ‘controlled’ or ‘negligible’ BSE risk status falls into a third category: ‘undetermined’ BSE risk status.
View the list of OIE Members with a BSE risk status in the Official Diseases Status section of this page
Last update : 06/08/2018
In accordance with the OIE procedure for official recognition of disease status, this page provides access to the List of OIE Members officially recognised as having a negligible or controlled bovine spongiform encephalopathy (BSE) risk status by the OIE through the adoption of a resolution by the World Assembly of Delegates (Assembly) of the OIE at the General Session in May every year.
A Member wishing to be officially recognised as having a BSE risk status by the OIE should submit the questionnaire laid out in Chapter 1.6. of the OIE Terrestrial Animal Health Code (Terrestrial Code) and comply with all requirements specified in the Terrestrial Code for BSE. The OIE Scientific Commission for Animal Diseases (Scientific Commission) is responsible for undertaking, on behalf of the Assembly, the assessment of OIE Members’ applications for their compliance with OIE standards. The assessment carried out by the Scientific Commission is based on the recommendations formulated by a relevant ad hoc Group composed of world specialists in disease control.
As the official BSE status of a country or zone is determined on the basis of an overall assessment of risk, the occurrence of a new BSE case implies a re-assessment of the official risk status only in the event of a change in the epidemiological situation indicating failure of the BSE risk mitigating measures in place.
When the Scientific Commission determines that the conditions are not met anymore to demonstrate compliance with the relevant requirements of the Terrestrial Code, a disease status may be suspended. The Scientific Commission may decide to reinstate the suspended status when a Member has submitted an application which fulfils all the requirements requested for the recovery of official disease status laid out in the relevant Chapters of the Terrestrial Code. The suspensions and recoveries of disease status are announced by the Director General of the OIE in consultation with the Scientific Commission and the list of these is kept up to date until adoption of a new resolution by the Assembly the following May.
Members with a disease free status officially recognised by the OIE must submit an annual reconfirmation form by the end of November every year.
Map of BSE official status
List of Members with a BSE risk status
According to Resolution No. 17 (88th General Session, May 2021)
Negligible BSE risk
Members recognised as having a negligible BSE risk in accordance with Chapter 11.4. of the Terrestrial Code :
|Canada||Korea (Rep. of)||Serbia (3)|
|Estonia||New Zealand||United States of America|
(2) Including Azores and Madeira.
(3) Excluding Kosovo administered by the United Nations.
(4) Including Balearic Islands and Canary Islands.
Controlled BSE risk
Members recognised as having a controlled BSE risk in accordance with Chapter 11.4. of the Terrestrial Code :
Zone(5) with a negligible BSE risk
Members recognised as having a zone with a negligible BSE risk in accordance with Chapter 11.4. of the Terrestrial Code :
China (People’s Rep. of):
A zone designated by the Delegate of China in a document addressed to the Director General in November 2013, consisting of the People’s Republic of China with the exclusion of Hong Kong and Macau.
United Kingdom (Map)
One zone consisting of Northern Ireland as designated by the Delegate of the United Kingdom in a document addressed to the Director General in September 2016.
One zone consisting of Jersey as designated by the Delegate of the United Kingdom in a document addressed to the Director General in August 2019.
Zone(5) with a controlled BSE risk
Members recognised as having a zone with a controlled BSE risk in accordance with Chapter 11.4. of the Terrestrial Code :
United Kingdom (Map)
One zone consisting of England and Wales as designated by the Delegate of the United Kingdom in documents addressed to the Director General in September and October 2016(6);
One zone consisting of Scotland as designated by the Delegate of the United Kingdom in documents addressed to the Director General in September 2016 and October 2016 and in December 2018.
(5) For detailed information on the delimitation of the zones of the Members recognised as having a negligible or controlled BSE risk, enquiries should be addressed to the Director General of the OIE.
(6) Following a report received from the OIE Delegate of the United Kingdom on the detection of a classical BSE case in Somerset, England on 17 September 2021, and based on the additional information submitted by the OIE Delegate of the United Kingdom, the Scientific Commission for Animal Diseases concluded that the zone of England and Wales complies with the requirements of Article 11.4.4. of the Terrestrial Animal Health Code for maintenance of the “controlled BSE risk status”, as recognised by the OIE World Assembly of Delegates in terms of Resolution No. 17 in May 2021.