Interview – May 2023
Thanks to the successful implementation of effective control measures, bovine spongiform encephalopathy (BSE) has turned from a public health emergency of international concern to a disease with contained presence and sanitary impact. First circulated in 2019, a revised standard on the disease has been adopted by the World Assembly of Delegates during WOAH’s 90th General Session.
Covering updates that include the criteria for determining disease risk alongside recommendations for disease surveillance and safe trade, the new text adopted represents a significant achievement. It reflects the work of the Organisation in tackling complex issues, building consensus among Members and finding up-to-date, science-based solutions that are beneficial to both animal and human health.
The revision of the standard was driven by WOAH Specialist Commissions. We have interviewed Dr Cristóbal Zepeda, President of the Scientific Commission for animal diseases and Dr Etienne Bonbon, President of the Terrestrial Animal Health Standards Commission.
What is the impact of BSE today?
Cristóbal Zepeda: At the beginning of the BSE epidemic in the late 1980s and early 1990s, the majority of cases were detected in a few countries, most predominantly in Europe. Today, the incidence of BSE has dropped to nearly zero, as most countries have implemented measures to avoid the recycling of specified risk materials (SRMs).
Etienne Bonbon: In the past, the uncertainty around the epidemiology of BSE justified an important level of precaution taken to handle the disease. Today, its quasi-zero incidence worldwide minimises the risk of disease and calls for a different level of precaution to face a novel scenario.
What was the rationale for revising the standard on BSE?
C.Z.: The standard on BSE was updated to align it with the current scientific knowledge and an evolving epidemiological context. Several changes were proposed. The first one covers the need for a complete disease risk assessment, including entry and exposure assessments, to determine the risk status of a country or a zone. The second one allows for a simplified surveillance to better match with the reality in the field, while ensuring that minimum sanitary requirements are put in place by countries. Indeed, the cost of implementing a point-based surveillance system is significant and some countries with small cattle populations can simply not comply with such requirements. We have developed guidelines to support countries in the transition to this new system. The last important change is the removal of atypical BSE from the list of diseases which require a compulsory notification to WOAH. Atypical BSE occurs spontaneously in cattle populations at a very low rate. In addition, the only evidence of potential recycling of specified risk materials was found under experimental conditions that would be extremely unlikely to be replicated under field conditions.
E.B.: When talking about the changes brought about by the revised standard on BSE, it is important to note that atypical BSE has been delisted also because it was found to be a very rare and sporadic condition, with no significant impact on animal or public health.
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. Whilst classical BSE was identified as a significant threat in the 90s, its occurrence has markedly decreased over the past years and is now estimated to be extremely low.
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 plays a significant role in the epidemiology of BSE, the potential for recycling of atypical BSE cannot be ruled out, and therefore measures to manage exposure risk in the feed chain continue to be recommended as a precautionary measure.
What were the challenges along the way?
C.Z.: WOAH has a procedure for official recognition of BSE risk status. In the context of the revision of this standard, we had to ensure that the Members already having an official BSE risk status would still remain compliant with the revised BSE standard. This involved a significant work to retrospectively assess the dossiers submitted by these Members, particularly those that were recognised on the basis of a negligible entry assessment and not a negligible exposure assessment.
E.B.: WOAH strives to find consensus among its Members. The achievement made with the BSE standard is the result of a multi-step process which involved many dedicated expert discussions, extensive consultations with Members, and even a first discussion with the Assembly last year. It shows how the different governance bodies work at the Organisation, and also highlights the role of the Specialist Commissions in the process. These Commissions play a key role to ensure that the standards are scientifically sound, and to build a common understanding trough consultation with Members.
Will the new BSE standard have an impact on the level of surveillance of the disease?
C.Z.: WOAH international standards related to the surveillance of animal diseases – including BSE – are crucial to determining the absence, presence and distribution of animal diseases and related risks, as well as detecting emerging diseases as early as possible. In the current epidemiological context for this disease, there was a growing need among Members to have the standard modified.
E.B.: The justified simplification and cost reduction of surveillance methods will not lead to a reduction in its effectiveness. Rather, this more flexible system based on field clinical screening reflects current scientific information and responds to a diversity of needs across countries.
What will be the impact of this new standard on international trade?
C.Z.: The changes in the surveillance requirements will provide an incentive for countries that have not gained an official risk status to apply for one. By removing atypical BSE as a listed disease, countries will not impose unwarranted trade restrictions.
E.B.: With the adoption of the revised standard, the benefits will be much higher than any risks of disease introduction or emergence. If it is well applied, access to trade will be facilitated thereby accelerating economic development, food security will be improved, while the likelihood of new BSE cases will continue to decrease.
The interview was edited and condensed for clarity and length.
bovine spongiform encephalopathy (BSE)