Thursday 28 August 2008

Atypical scrapie

Tuesday 5 December 2006

Scientific tests have identified a brain disease in sheep called atypical scrapie. The disease comes from the same family of diseases as 'classical' scrapie in sheep (which has been around for over 200 years and is not known to be harmful to people) and BSE in cattle (from which humans can get the fatal disease variant CJD).

Precautionary measures currently in place to protect against TSEs
Possible additional precautionary measures
Food Standards Agency position statement on contingency planning

‘The Food Standards Agency is not advising people to stop eating lamb or mutton (sheep meat) and goat meats or products derived from these animals.’

Atypical scrapie is not BSE, and there is an absence of scientific evidence that it can be transmitted to humans or that it is of any risk to humans. However, a risk can't be ruled out.

The Agency, and other organisations across Europe, are organising research into atypical scrapie, but it could take years for any conclusions to be reached.

As part of its commitment to be open and transparent, the Agency will update consumers in line with the latest developments in research into atypical scrapie or as new information arises.

The Agency Board discussed atypical scrapie at its open meeting in March 2006. At its June 2006 open meeting, the Board asked the Agency to issue information to keep consumers and stakeholders up to date with what we know about atypical scrapie.

The Agency has summarised below its latest understanding of atypical scrapie. This summary has been drawn up in consultation with scientists, consumer bodies and industry organisations.

Atypical scrapie has been identified in sheep throughout Europe. How common it is outside Europe is not known. European countries test extensively for atypical scrapie. Many non-European sheep-producing countries do not.
Scientists estimate that only a small proportion of sheep in Great Britain (approximately one in 400) may be infected with the disease.
Diseases similar to atypical scrapie include 'classical' scrapie, which has been around for hundreds of years and is not known to infect people, and BSE in cattle, which can be transmitted to people when it is known as vCJD. All of these diseases have long incubation periods, but they lead to irreversible brain damage and death in infected animals. vCJD also leads to the death of infected humans.
Scientists have so far found no evidence that atypical scrapie can be transmitted to people or that it is dangerous to people, but some believe that such a risk is possible in theory.
The Food Standards Agency and the Department for the Environment, Food and Rural Affairs (DEFRA) in the UK are among a number of organisations within Europe funding research into atypical scrapie using a range of different experimental methods to assess whether atypical scrapie might pose a risk to people.
The Agency is not advising people to change their eating habits with regard to lamb or mutton (sheep meat) and goat meat or products derived from these animals.
Some measures are already in place to protect us against BSE. For example, even though no sheep have been found to have BSE, many parts of these animals are removed as a precautionary measure and not allowed to go into our food. These are the parts that would also most likely be infected with atypical scrapie if an animal had the disease.
Additional measures would be considered by the Agency if atypical scrapie were found to be of risk to people.
If there were any risk to humans from sheep being infected with atypical scrapie it would be greater in older animals. It has also been calculated that in sheep with scrapie (and in sheep with BSE, when they are infected experimentally with the disease) it would be impossible to remove all traces of the infectivity from the animals' intestines when the intestines are made into sausage casings. This may also apply in the case of atypical scrapie.
While there may be no risk to humans from atypical scrapie, anyone wishing to take extra precautionary measures might decide to stop eating meat from older sheep (mutton) or sausages covered in wet skins (casings) made from sheep intestines. Not all pre-packed sausages are labelled to say what their skins, or 'casings' are made from. However, some labels do provide such details, and butchers may also be able to provide information on what casings are used on their sausages.
The Agency is not recommending that people take such actions, and recognises that it is not always possible to know if the meat comes from older sheep.
The majority of meat from sheep eaten in the UK is lamb. Meat from older sheep (mutton) represents just less than 20% of the total sheep market. Meat from about 6000 goats goes into the food chain in the UK each year, plus imported meat from goats, which total 257 tonnes in 2007.
Anecdotal evidence suggests that the Indian and Pakistani communities in the UK eat a proportionately higher amount of mutton than their counterparts in other communities. There is similar anecdotal evidence that people from the UK's African and Caribbean communities eat proportionately more meat from goats.

The science behind the story

Atypical scrapie: the science

The research into atypical scrapie cannot provide quick answers. It may take years for some of the research to come up with results and the outcomes might not be clear even then. This is why the Agency will continue to rely on the opinions of its expert scientific advisers when offering advice to the public.
Cattle, sheep and goats are susceptible to a group of brain diseases known as transmissible spongiform encephalopathies (TSEs). The best known of these diseases is BSE in cattle. Another is 'classical' scrapie, which has been around for hundreds of years and is not known to infect people,
The Spongiform Encephalopathy Advisory Committee (SEAC), the independent expert scientific advisory committee that advises the Agency, has found no evidence that atypical scrapie is harmful to humans. But it also explains that such a risk is possible in theory, so it cannot yet be ruled out.
A SEAC Sheep Subgroup has been in existence since 1999, and it reviews progress on research and surveillance programmes for TSEs in sheep and goats and may also recommend further work needed.
According to the SEAC Sheep Subgroup it is important to try to establish whether atypical scrapie has been in existence for some time or if it is a new disease - by applying new tests to any appropriate historical samples, and to maintain surveillance to establish whether the prevalence of atypical scrapie is changing.
It has recently been shown that atypical scrapie can be experimentally transmitted to mice and to sheep. This is why the Subgroup explains that the possibility must be considered of atypical scrapie being able to be transmitted to people. Experiments to provide information on this possibility may take several years to complete.
The SEAC Sheep Subgroup considers that urgent clarification is required on whether atypical scrapie is present in the lymph nodes of sheep, and whether there are differences between different types of sheep. These tissues are not covered by the current specified risk material (SRM) requirements. The Agency has commissioned research investigating the distribution of atypical scrapie infectivity in sheep tissues along with models to determine human susceptibility to the disease. These data will provide much needed information on the potential food risk associated with atypical ascrapie in sheep and reveal any clinically important differences between atypical scrapie and classical scrapie.

Precautionary measures currently in place to protect against TSEs

A number of precautionary measures have been in place in the UK for some time to protect consumers from the theoretical risk of BSE in sheep, even though no sheep in the UK have been found to have the disease. These measures include:

the removal of certain parts of the animal called specified risk material (SRM) and the exclusion of these parts of the animal from the food chain. The removal of this SRM is also likely to keep most infectivity from atypical scrapie out of our food, where sheep are infected with this disease. The parts of sheep and goats already removed as SRM include (all ages) the spleen; ileum; (over 12 months or with a permanent incisor erupted): the skull including the brains and eyes; tonsils; spinal cord.
A feed ban prevents the spread of scrapie or BSE through animal feed by banning the inclusion of certain animal proteins.
Compulsory reporting - any cases of suspected TSE must be reported, these are then subjected to confirmatory testing and, if positive, to differential testing.
Active surveillance - a random sample of 10,000 sheep over 18 months slaughtered at abattoirs and 10,000 fallen stock sheep (ie dead on farm) and 500 fallen stock goats over 18 months are tested for TSE. All samples that prove positive for TSE are further tested to determine if scrapie is present and if BSE is suspected, further discriminatory tests are carried out.
Breeding/culling programs applied following a finding of TSE - an epidemiological investigation is undertaken and for classical scrapie, under current legislation, the animals from the identified flock(s) are either genotyped and those of non-resistant genotypes are culled or the whole flock/herd is culled. For flocks/herds with atypical scrapie, the EU rules provide for monitoring and also the possibility of a whole flock/herd cull.

Possible additional precautionary measures

These additional measures might be considered by the Agency in the very unlikely event that atypical scrapie were found to be of risk to humans. These measures could include:

A complete ban on older sheep entering the food supply.
Increasing the list of SRM to cover other tissues known to carry scrapie
Infectivity (although it is recognised that some lymph nodes associated with edible tissue would be difficult to remove).
TSE testing of all older animals, with only those with a negative result being allowed into the food supply.

Food Standards Agency position statement on contingency planning

The Food Standards Agency Board has approved a position statement on the work being done to improve the Agency’s knowledge of atypical scrapie and the procedure the Agency would follow if it received new information that affects its understanding of the risk. This document, which can be found below, will be kept under review and updated as scientific knowledge about atypical scrapie changes.

External links The Food Standards Agency has no responsibility for the content of external websites

(External) National Scrapie Plan (DEFRA website) (External) Get Adobe Acrobat reader You may need the free Acrobat Reader to view a pdf

Graphic version of this page

Atypical scrapie

The science behind the story

Precautionary measures currently in place to protect against TSEs

Possible additional precautionary measures

Food Standards Agency position statement on contingency planning

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External links The Food Standards Agency has no responsibility for the content of external websites

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