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Scientific Committee on Animal Health and Animal Welfare

Previous outcome of discussions ( Scientific Veterinary Committee)

The TSE Status of Australia and the USA and The Scrapie Eradication Programme in Norway - Report of the Scientific Veterinary Committee - Adopted 17 September 1997

REPORT OF THE SCIENTIFIC VETERINARY COMMITTEE OF THE TSE STATUS OF AUSTRALIA AND THE USA AND ON THE SCRAPIE ERADICATION PROGRAMME IN NORWAY

In the light of the review of the recommendations for surveillance of Scrapie and BSE, to assess the programmes submitted by Australia, and the USA in regard to their BSE/scrapie status or, in the case of Norway, their eradication policy in regard to scrapie.

The Committee notes that it is not possible to prove a zero risk and it is therefore difficult for a country to demonstrate freedom from TSE. The committee further notes that is easier to establish freedom of a flock or herd from TSE than of a country. However, in Australia there is a formidable border control programme leading to the view that risks from the importation of live animals, meat and bone meal and other ruminant products will be very low. Risks from endogenous sources are also considered to be low based on the lack of evidence of clinical TSE in animals over a long period of time. This low risk is not quantifiable. The level of confidence that a low risk of animal TSE occurs currently or will occur in the future can be increased. How this can be done is stated below, first for BSE then for scrapie. The committee further advises that reference should be made to document XXIV/B3/ScVC/004/1997 "Report of the ScVC on surveillance of TSE" for guidance on the nature and extent of the surveillance considered necessary and how this could be achieved.

Document A contains several errors of fact (some of which have been corrected or amended in other documents). There are also inconsistencies between documents. Some statements in Document A if believed and acted upon alone ( e.g. 1.4.4 "It is expected that an occurrence of BSE would be associated with imported livestock", could give a false sense of security.

It should be formally confirmed that the pathological procedures used to diagnose BSE and scrapie are consistent with those recommended in the OIE Manual of Standards.

1. Whereas the monitoring of imported animals appears to be rigorous, there is no indication that native-born animals are individually and permanently identified in a manner that would enable effective tracing from the farm of birth to other herds or, from the place of death back to the farm of origin and farm of birth so that any further studies deemed necessary can be undertaken.

2. The committee notes that Australia is imminently adopting the guidance in regard to surveillance and monitoring for BSE specified in the OIE Animal Health Code of May 1997. However, prior to 1997 this has not been done to this standard. Thus prospective information produced from these new studies will significantly improve the confidence that BSE does not occur in Australia.

3. The committee notes that no evidence is provided to support the statement that there is a naturally low incidence of neurological disease in adult cattle (Document D, Annex 2 Para 2, last para). If this is not the case an adverse bias in the target population selected to examine for BSE could occur with resulting lack of confidence in the data.

4. The historical number of brains examined is too low and not adequately targeted. The new proposals correct this deficit in line with OIE Guidance but examination of more brains than the minimum would give increased assurance.

5. The committee emphasises that there is a need for a continuous awareness campaign for farmers and veterinarians in order to maintain awareness of the clinical signs of BSE at a consistently high level.

6. Compensation for suspect animals should be clearly up front and at such a level that it acts as a positive incentive to report such suspect cases.

7. The age of animals which historically provided brains for examination has not been provided and thus the value of the data provided is diminished ( cf Table in para. 4.3 of Document C which covers different periods for different States/Territories with no indication of the age of the animals or the number examined by year). The committee notes that the future proposals in this regard (Document D) are entirely consistent with OIE recommendations and strongly supports this approach.

8.Document D, Annex 2, Para. 2. B) ii) b implies that there is no pre-slaughter ante-mortem inspection of cattle destined to produce beef for the home market. If this is the case and is corrected the quality of surveillance will improve and greater confidence will result. Such a measure is strongly advised, if not in place.

9.Where there is a doubt about a diagnosis made by microscopic examination of the brain, or if no pathological diagnosis is reached, the certainty that a TSE does not exist can be improved by adopting supplementary methods of diagnosis as specified in the OIE Manual of Standards. The committee recommends this is done including the use of methods to detect PrP ^Sc.

10.An analysis of diagnoses made in the surveillance programme, if published, would enable comparisons to be made with data from different years in Australia and between different countries. It would also enable early detection of trends in diagnoses which might suggest the need to adopt a more aggressive investigation.

11.The possibility of cross contamination of ruminant concentrates with meat and bone meal (while not itself a risk if no infectivity is present) could lead to exposure of cattle should the tissues of any animals unexpectedly infected with a TSE agent be processed by an ineffective method. For added protection consideration should be given to reducing this risk. The parameters required by law to process ruminant material destined to produce meat and bone meal for feeding to farm animals should be specified and ideally should be demonstrated to effectively inactivate TSE agents. The Committee notes that there is still not a mandatory ban on feeding MBM to ruminants in force throughout the country.

12.It is possible that cattle imported from the UK, Switzerland and France between 1980 and 1991 could have entered the human and animal food and feed chain before controls in regard to BSE were in place. However the total numbers were small from France and Switzerland and the UK (131 animals). The analysis by breed (p.9 of doc. C) is incomplete for animals now dead but there is a strong bias in those remaining towards beef cattle (low risk). There is no evidence that BSE has occurred in those slaughtered or died before 1990.

The committee is impressed by the AUSVET PLAN for BSE (and scrapie) and the most recent proposals to improve the surveillance in Australia in line with the recommendations in the OIE International Animal Health Code Chapter on BSE. It particularly notes the efforts to harmonise the training in diagnosis to a common high standard. There is no evidence for the occurrence of BSE in Australia and the risk of future occurrence is low. This low risk can be further lowered by adopting some or all of the recommendations above and adopting the principles in Document XXIV/B3/ScVC/004/1997.

Many of the comments in regard to BSE above are relevant to scrapie too and should be considered along with the guidance in document XXIV/B3/ScVC/004/1997. In addition the committee recommends consideration is given to the following points:

1.The description of clinical signs in Document A is inadequate as are differential diagnoses ( e.g. para 1.4.4 space occupying lesions are not mentioned) but very much improved in Document D. This is welcomed. However, a clear written description and visual demonstration of the clinical signs must be seen to be communicated to all sheep farmers and veterinarians by a continuous awareness programme. Attention is drawn to the potential occurrence of scrapie in found-dead sheep which death should not be assumed to be due to other diseases without investigation. (See below).

2.Much more aggressive targeting of the population of sheep from which brains must be examined is recommended. This applies to all types of flocks including extensive ones where found dead adult sheep should be examined pathologically for evidence of scrapie even if the brain is autolysed.

3.The numbers of adult sheep brains examined historically is too low (you will only find it, if it exists, if you look for it diligently) and it is noted this is to be increased (Document D, p. 16). The committee believes greater confidence can be provided about the scrapie-free status of Australia if many more brains were examined from targeted animals including feral goats.

4.The committee stresses the importance of targeting sheep of an appropriate age and that if any microscopic examination of the brain is inconclusive or impossible other methods must be used to eliminate scrapie as a cause. The committee recommends that the diagnoses made should be tabulated and published for comparative purposes and to demonstrate, where possible, that the lesions or disease which could have contributed to, or caused, the clinical signs i.e. the committee considers that formal declaration of the actual and differential diagnoses is important in raising confidence about statements of freedom.

5.There is no indication that individual sheep are permanently identified in a manner that could allow tracing (cf BSE Para. 1 above). This is regarded as important should it be necessary to make further examinations in sheep (or goats) on the farm of birth or origin.

6.The committee strongly recommends that PrP genotyping by breed is established so that the overall distribution of PrP genotypes, by breed and geographical location in Australia, based on current knowledge, is known. It is noted that clinical TSE in sheep results from the interaction of two independent variables - the PrP genotype and the strain of agent.

7.As with BSE the committee does not accept the statement (Document B, paras. 1.4.4 and 1.7) that any occurrence of scrapie in Australia can be reasonably expected to be an isolated event associated with livestock imported in the last decade. There are many other possible routes (some of which are mentioned in Documents A - D) and however unlikely they must be seriously considered. The committee notes the very stringent controls placed on imported animals and products and endorses this approach.

8.Although not yet validated there are now published methods that will detect PrP ^Sc in brain and peripheral tissues of clinically or pathologically silent sheep infected with the scrapie agent. The committee recommends such methods are used as part of the surveillance programme when validated.

9.The use of validated transgenic mice expressing ovine and/or caprine PrP could be considered to enhance detection of infectivity in scrapie-suspect or imported animals in the future when they have been validated.

Despite several historical weaknesses in the surveillance for scrapie in Australia the committee has taken account of the extremely stringent (and endorsed) importation and quarantine policy adopted over many years, the rearing and feeding methods, the quality, experience and training of Australian pathologists and the absence over decades of the clinical evidence for the occurrence of scrapie.

It further notes the new approaches that are in accordance with the OIE International Animal Health Code Chapter on BSE and similar ones for scrapie surveillance. Whereas the committee considers that confidence in the statement that Australia is a country free of BSE and scrapie could be further increased above the current level by considering and adopting the recommendations above, it has sufficient confidence to state that the probability of any potential health risk associated with specified risk material (SRM) as described in the report of the ScVC Document VI/6665/96, Rev6 derived from animals reared and slaughtered in Australia is at present very low. The confidence level in assessing the Australian situation regarding the TSE situation can be considered as broadly similar to New Zealand, though slightly less satisfactory at the present time.

The United States differs from Australia and New Zealand in that three naturally occurring animal TSE have been diagnosed in the country. These include scrapie and chronic wasting disease, which still exist and TME which has not been reported since 1985. No naturally occurring TSE of cattle has ever been confirmed in North or South America: One cow each in Canada and the Falkland Islands has developed BSE. Both were exported from the UK in the incubation stage of the disease in early years of the epidemic.

For the purpose of our judgements we have ignored any risks there may have been, or currently exist, in regard to CWD and TME and have thus considered only BSE and scrapie risks. However, there appear to be no current risks from TME as the disease is absent. To date there is no evidence of any epidemiological link between the occurrence of CWD in deer and elk and in cattle and sheep. Strain typing appears to indicate differences between this and BSE and known scrapie strains. Overall, on current evidence, CWD does not have a source in or transmit naturally to cattle. In any event CWD seems to be localised to Wyoming and Colorado but does exist in the wild.

496 cattle have been imported into the USA from the UK in the risk period 1981-1989 (and not thereafter) but these are under very strict surveillance and only 17 are currently alive. No evidence of BSE has been found in any bovine animal in the USA but tissues from some of the animals imported from the UK could have entered the rendering system from 1981 until the aggressive approach to surveillance was developed in 1990.

The USA had adopted a stringent control on the importation of cattle and cattle products in regard to BSE since 1989 which is directed at countries which have declared the occurrence of BSE. There is some doubt that all cases of BSE have been reported in Europe and possibly other countries (Schreuder et al (1997) Vet. Rec. 141, 187-190) and some countries which have not reported the disease may have had infected animals which could have contributed to recycling infection to other cattle via infected feed. Some such cattle may have been imported. However of the 496 animals imported, only 13 were dairy animals and these may have been imported before contaminated feed might have been in circulation. The remainder were beef breeds.

The USA has not submitted evidence that the rendering procedures used in the USA to prepare meat and bone meal from ruminant waste materials are effective at inactivating TSE agents. The committee considers it is unlikely that they all do. Furthermore, there is no specified risk material ban which would, if in existence and effectively operated, have reduced any infectivity entering the rendering process to a very low level. It is noted that there has been a voluntary ban by the rendering industry preventing the processing of adult ovine carcasses and material for some nine years. This is welcomed. The quality of the enforcement is not indicated but although any risk from sheep will most probably have been reduced it will not have eliminated the risk of exposure of cattle via feed. The sheep population in the US has dropped in recent years from 11 million to 8 million, thus reducing the total amount of sheep material in the rendering system.

The US has conducted transmission experiments with US scrapie isolates into cattle. A neurological disease clinically and pathologically dissimilar to UK-type BSE has been produced in some cattle following parenteral challenge with brain material and not so far (>6 years) following oral challenge. There is no evidence whatever that this experimental disease has occurred naturally in the cattle population of the USA or anywhere else. The neurological signs of this experimental disease can be more easily confused with other clinical syndromes in cattle. Confirmation of diagnosis is only likely to be made in most instances if a sensitive method is used to detect PrP ^Sc in the brain. It is noted that this method was applied in 1994 and 100% usage was established in 1997. The committee is satisfied that microscopic examination of the brain would have revealed UK-type BSE had it occurred at a sufficient incidence at any time since surveillance for TSE was initiated/increased above the norm. This surveillance system should now be able to detect other possible TSEs in cattle if they exist.

The original risk assessments for BSE in the USA concentrated on the risks from sheep with scrapie and indicated a variable geographical distribution in the risk dependent largely upon the ratio of sheep to cattle, the geographical distribution of sheep and the way they were farmed. Whereas the BSE risks from sheep with scrapie were calculated to be very much lower than the risks in the UK they were still measurable. The committee is most concerned about the possible recycling of any infection derived from any source in cattle. They perceive that until recently there has been little to safeguard cattle in the USA fed concentrate rations, from any TSE infection in feed.

Furthermore, it is claimed that, unlike in the UK calves were seldom fed meat and bone meal, (though cross contamination of calf diets cannot be ruled out). If this is so, exposure would have occurred later in life and if the older animal is as susceptible as the younger one and the mean incubation period is maintained at five years the age of animals that would develop BSE would, on average, be higher than in the UK. Dairy cattle in the US are culled at a younger age than in the UK and therefore fewer animals might be expected to develop clinical signs of BSE. Thus a low incidence of affected animals may not be detected and would pose a risk as tissues from them could carry infectivity.

The USA has developed a surveillance programme for BSE since 1990 and has examined a significant annual number of brains from targeted cattle of an appropriate age for evidence of BSE. This gives a statistical answer to the question of the occurrence of BSE in the country and is in line with or above the requirements of the OIE International Animal Health Code Chapter on BSE. However, whilst this gives reassurance that (at a certain degree of confidence) that BSE infection has not existed in cattle in the USA historically it still does not provide assurance at the present time. This is because risk factors for BSE occurrence have persisted even though probably at declining levels with time, in the interval of time equivalent to the incubation period. These risk factors include the existence of scrapie (note is taken on the reduction of risk by the voluntary ban on rendering ovine material and now, compulsory ban via the Federal Rule of 4 August 1997) both in sheep and in goats, probable inadequate security of the inactivation capacity of rendering processes, the use of fallen stock and other dead animal carcasses and tissues for rendering, the feeding of mammalian meat and bone meal to ruminants, the absence of any specified risk materials ban and the risk of recycling cattle material to cattle via feed including by accident due to cross-contamination of ruminant concentrate diets with infected meat and bone meal.

The committee notes and endorses the provisions of the recently implemented FDA Federal Rule and notes that this immediately addresses the risks via feed in regard to animal health. This reduces the risk of the possibility of a BSE epidemic.

If the Rule is effectively enforced (evidence is required to show that it has been) this will very much improve the disease security in regard to TSE for all ruminant species. The committee notes also the legal requirement to prevent any possible cross-contamination of ruminant diets with prohibited material. However, this rule has only existed since 4 August 1997 and therefore complete protection of ruminant animals from exposure to TSE agents in feed cannot be assured before this date. Assurance on a national basis could be given for animals born after a certain date when it could be proved that the Federal Rule was effectively enforced.

The USA has not made clear the cattle identification and recording system in regard to within-State movement, between State movement and for imported animals from countries other than the UK. The committee is satisfied that cattle imported from the UK are effectively monitored but is uncertain about cattle imported from other countries (where scrapie may exist and BSE could theoretically occur in the future) including those with land borders with the USA. It is important that these countries should have equivalent or higher health standards ( e.g. feed ban) re BSE than the USA. The committee considers it is important to be able to trace the movement of any animal from its natal herd to its current destination and from the point of death backwards to its natal herd. The purpose of this is to be able to visit and examine cattle in source herds if any actual or suspect case of BSE should arise.

The committee is satisfied with the pathological procedures in place to detect any form of TSE in cattle in the future. It notes that increasing the number of brains from targeted animals can only increase the confidence that a low incidence of disease would be detected. Currently an average of 650 brains per year for the last three years from a total adult cattle population of 45 million, whilst greater than the minimum specified in the OIE International Animal Health Code, is providing a 95% confidence that the incidence is not greater than 1 in 1 million. With the potential for cattle to cattle recycling of infection until 1997 the committee considers a larger (but still practical) number of brains should be examined. In this regard the meaning of the last paragraph on page 2 of Document A is unclear.

In regard to endemic scrapie the committee is aware of the various scrapie control schemes that have been adopted in several countries over many years but none has fully succeeded in eradicating the disease. However, new data on PrP genotyping is being acquired which may in the future, as in other countries, contribute to more effective control of disease and possibly lead to eradication. The committee notes that in Document B Para. 1b first paragraph, scrapie exists at a low level has no meaning and is unsupported by any data. At present despite the results to date of successful transmission of US scrapie to cattle being unlike UK BSE there is insufficient information to indicate that US scrapie is distinct from European scrapie. In many respects ( e.g. clinically, pathologically and occurrence in certain PrP genotypes) it appears indistinguishable.

In Document A there is no clear distinction between active and passive surveillance as defined in Document XXIV/B3/ScVC/004/1997 though the committee notes the additional surveillance accomplished by veterinary schools and the like, which however is not controlled by the federal authorities, though they do issue a report.. In this regard a federally-audited publication of an analysis of the actual diagnoses made in each year could provide increased confidence that no TSE was occurring. The committee emphasises the importance that the awareness programme be continuous and be assessed in regard to its effectiveness. In this regard the committee agrees that reporting of suspect cases should incur no costs to the farmer and that compensation should be paid at the market rate for any animal killed at the instigation of the authorities i.e. the incentive to report must be clear and unambiguous.

In regard to meat and bone meal the committee notes that cattle provide a large proportion of the product and that US cattle in general consume less per head than used to be the case in dairy cattle in the UK. Where does the excess meat and bone meal go and to what species is it fed? If exported and fed, even accidentally, to ruminants (especially cattle) in other countries surveillance for BSE there could be an additional means of monitoring US-prepared meat and bone meal in regard to TSE agents. The committee notes the problems that could arise via blending with meal from other countries but this would only be important if BSE occurred in the country importing US meal or compounded rations containing it.

1. Scrapie occurs in sheep and sometimes goats in the USA and there is no reason to believe it is any different from scrapie in Europe, though differences in the strain of agent may exist. The distribution of infectivity in Suffolk sheep in the USA has been thoroughly investigated and it is partly on this work that the UK and subsequent EU control measures in regard to specified risk materials were based. It should be emphasised that there is no evidence that classical scrapie is a public health risk.

2.Neither BSE nor any TSE of a bovine animal has ever been detected in the USA. A surveillance and monitoring programme for BSE is in place and exceeds that specified in the OIE International Animal Health Code Chapter on BSE. Whereas this has probably been effective in detecting BSE should it have occurred, it is indicative of a historical absence of BSE and is not an absolute guarantee for the present situation. This is because several endemic risk factors have existed, in particular those resulting from feeding of cattle with meat and bone meal, deliberately or accidentally, until 4 August 1997 when a Federal Rule came into force. While it is not possible to quantify the risk resulting from the presence of these risk factors, they must be estimated, in the absence of bovine recycling, to be low. Whether or not the risk will result in BSE will not be known until the incubation period (mean 60 months) resulting from any effective exposure is complete and brains have been examined. Thus at present the committee cannot guarantee that cattle from the US have not been exposed to and thus do not carry BSE infectivity, though there is no positive evidence that they do so.

The committee notes an effective surveillance programme is in place and that the recent Federal Rule (4 August 1997) if effectively enforced would protect cattle from exposure via feed. Therefore cattle born in the USA after the date upon which the Rule became effectively enforced would be at a low risk from developing BSE.

The Committee was asked to comment on the eradication programme for scrapie in Norway.

A - The Norwegian position on trade in live sheep and goats. Information about the Norwegian Programme to eradicate scrapie (26/9/96)

B - An update on the current position with regard to the programme (4/9/97). This was provided in Norwegian and was described by Dr Ulvund. An unofficial translation in English is now available.

Dr Ulvund gave some updated information on the on the scrapie situation in Norway, including a short progress report on the programme so far.

The proposals for eradication were considered in regard to scrapie control schemes elsewhere (including Iceland) and in regard to the six rules proposed in the earlier report of the scientific Veterinary Committee "Scrapie surveillance and control in the context of Council Directive 91/68/EEC".(Doc VI/4735/92). Where relevant all the rules were satisfied, otherwise satisfactory alternatives were presented.

It is proposed to examine 3.500 brains from abattoir killed sheep over 3,5 years old, selected randomly. In future brains from selected sheep from farms could be targeted. The subgroup would strongly support this.

It was noted that the programme had some features reminiscent of those used in Iceland where there has been considerable success in the eradication of scrapie from flocks but which was incomplete on a national basis. However, good use of historical and contemporary prep genotyping was being undertaken which had not been part of the Icelandic programme. There were proposals for collaborative research on scrapie.

The committee concludes that the plan is a good one with many excellent attributes. Whether or not scrapie will be eradicated on a national or flock basis is impossible to predict. There are insufficient data and experience to make this judgement at the present time. It is possible that scrapie could be eradicated but even if it is not, new information being generated on the susceptibility of sheep to scrapie and methods of transmission between sheep could be more readily applied to assist in the final eradication of the disease in a shorter time than otherwise.

It may also be useful to consider the collection of peripheral tissues such as lymph nodes or tonsil. Due to the incubation period and pathogenesis of scrapie there may be a higher chance of detection with the peripheral tissues. These tissue samples could always be stored until tests are validated.

The committee recommends that the plan should be regularly reviewed to determine progress and in the light of new scientific information. The role of the small population of goats in the epidemiology of scrapie in sheep should also be considered.


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