Bovine spongiform encephalopathy aka BSE- WOAH (2023)

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.

BSE is a WOAH-listed disease and must be reported to the WOAH, as indicated in the WOAH 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 WOAH 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

Clinical signs

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;
• depression;
• 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.

Diagnostic

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 WOAH 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 WOAH 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-risk Status

BSE is a disease for which the WOAH 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 WOAH 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 WOAH Members with a BSE risk status in the Official Diseases Status section of this page

Last update : 06/08/2018

In accordance with the WOAH procedure for official recognition of disease status, this page provides access to the List of The World Organisation for Animal Health (WOAH, founded as OIE) Members officially recognised as having a negligible or controlled bovine spongiform encephalopathy (BSE) risk status by the WOAH through the adoption of a resolution by the World Assembly of Delegates (Assembly) of the WOAH at the General Session in May every year.

A Member wishing to be officially recognised as having a BSE risk status by the WOAH should submit thequestionnairelaid out in Chapter 1.6. of the WOAH Terrestrial Animal Health Code(Terrestrial Code) and comply with all requirements specified in theTerrestrial Codefor BSE. The WOAH Scientific Commission for Animal Diseases (Scientific Commission) is responsible for undertaking, on behalf of the Assembly, the assessment of WOAH Members’ applications for their compliance with WOAH standards. The assessment carried out by the Scientific Commission is based on the recommendations formulated by a relevantad hocGroup 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 theTerrestrial 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 theTerrestrial Code. The suspensions and recoveries of disease status are announced by the Director General of the WOAH in consultation with the Scientific Commission and thelistof 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 WOAH must submit anannual reconfirmation formby the end of November every year.

Map of BSE official status

List of Members with a BSE risk status

According toResolution No. 15 (89th General Session, May 2022)

Negligible BSE risk

Members recognised as having anegligible BSE riskin accordance with Chapter 11.4. of theTerrestrial Code:

Controlled BSE risk

Members recognised as having acontrolled BSE riskin accordance with Chapter 11.4. of theTerrestrial Code:

Zone⁽⁵⁾with a negligible BSE risk

Members recognised as having a zone with anegligible BSE riskin accordance with Chapter 11.4. of theTerrestrial Code:

China (People’s Rep. of):

Azone 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.

UnitedKingdom (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 theTerrestrial Code:

UnitedKingdom (Map)

(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 WOAH.