SEAC : Q & A on their recommendations 1998

SEAC: Q & A on their recommendations

1998

November

Q. What did SEAC say about the experimental results on infectivity in bone marrow at their November meeting?

A. SEAC provided a report to Ministers which updated their previous advice of December 1997 on the risk to public health from infectivity in dorsal root ganglia (DRG) and bone marrow. Further experiments on the infectivity in bone marrow only showed positive in the group killed at 38 months after infection with BSE, when clinical disease was evident in the cattle and not at any earlier or later times after exposure to BSE. SEAC felt that these results could be interpreted in three ways:

infectivity may occur occasionally in the bone marrow of clinically affected animals.

the test is only able to detect infectivity above certain levels and for BSE infectivity in the bone marrow of cattle it is operating on the borderline of its sensitivity.

in the case of the group of cattle killed at 38 months after exposure to BSE, the pooled tissue sample was accidentally contaminated at some point during post mortem procedures.

Q. What was their advice regarding bone marrow?

A. SEAC concluded that current evidence did not allow them to determine which of the above interpretations is correct and that the positive result at 38 months cannot be discounted and may indicate that infectivity in bone marrow occurs occasionally, when clinical signs are apparent and there are already very high levels of infectivity in the central nervous system (brain and spinal cord).

SEAC noted that infectivity had not been detected in bone marrow before cattle reached the clinical stage of the disease and that all clinically affected animals are already removed from the food chain. So too are the majority of infected cattle that are at the advanced stage of incubation when they are slaughtered under the Over Thirty Months Scheme (OTMS). Consequently the risk to public health from infectivity in bone marrow is likely to be very small.

Q. What did SEAC say about the risk from dorsal root ganglia (DRG)?

A. SEAC noted that infectivity was consistently demonstrated in dorsal root ganglia (DRG) of cattle in the pathogenesis experiment in the groups of infected cattle killed 32,36, 38 and 40 months after oral exposure to BSE. Any continuing risk to public health must be evaluated in the light of the number of animals likely to be carrying infectivity, their age, how far the disease may have progressed when they are slaughtered and how the carcase is processed for distribution and consumption.

SEAC concluded that it is still not known how many humans have become infected with vCJD as a result of exposure to the BSE agent, nor how much BSE infectivity is needed to cause the disease. Consequently it was still not possible to predict with any degree of precision the risks to public health from dorsal root ganglia and bone marrow. They did note that with the continuing decline in the numbers of infected cattle which are slaughtered for human consumption each year any risk from DRG and bone marrow would have reduced. It was felt that the pattern of results with bone marrow meant that the risk, if any, from this tissue is likely to be very small. Also, with the OTMS in place it was thought that the risk from DRG was also very small and negligible in comparison to the possible risk earlier in the epidemic.

Q. What did SEAC say about neural emboli?

A. In November 1998 the Committee considered preliminary research results on methods of slaughter and the possible association with neural emboli in blood. Neural emboli are small (possibly microscopic) pieces of tissue dislodged and carried into the bloodstream during the slaughter process.

SEAC noted research which confirmed previous findings that high pressure pneumatic stunners could, in some cases, result in the presence of emboli in the blood in the large veins draining the head. Though such stunners were not used in the UK SEAC concluded that the study of stunning and pithing methods in the UK should be extended to evaluate whether the trauma caused by these methods had historically represented any risk of contamination of bovine blood with BSE.

Q. Why did SEAC look at the possible historical risk from neural emboli rather than the risk now?

A. At their 09 November meeting SEAC noted that the number of infected cattle that might have infectivity in the brain when slaughtered for human consumption at the present time was very low. Therefore, the results of further research on neural emboli described above would not give rise to concern about the risk of transmitting BSE by current practice.

Q. SEAC considered the controls on beef over thirty months of age. What did they conclude?

A. The Committee identified criteria whereby the controls on beef over thirty months of age could be reviewed in the future. The Committee planned to begin to address this at their meeting in March 1999 but recognised that this issue required careful study and would almost certainly need to be considered over several meetings.

Q. SEAC last looked at the risk of spreading rendering condensate in September 1998. What decision did they reach on this issue in November 1998?

A. In September 1998 the Committee requested further information as to what went into the process which produced condensate before they could reach a conclusion about the safety of this practice with regard to grazing animals. In November the Committee noted both the procedures associated with the processing of fallen stock and the difficulty of establishing the origin of any protein found in condensate. They therefore concluded that the spreading of rendering condensate on fields where cattle might graze should be prohibited. The Committee concerns were related to the risk from BSE to animal rather than to human health.

Q. In November 1998 what did SEAC conclude about the use of human splenic extract in the Kveim test?

A. The Kveim test is a diagnostic skin test used in sarcoidosis. SEAC recommended that where human spleen extract was used as the raw material for diagnostic tests which may be administered to humans, the spleens used should be low risk material, preferably originating from a BSE free country and screened by immunocytochemistry prior to use.

Q. SEAC held its first press briefing after their meeting in November 1998. Why?

A. The Committee decided that it would be useful to hold a press briefing at the time of the publication of Committee statements which are published after each meeting. In doing so SEAC hope to improve understanding of how conclusions are reached and create public awareness of both the facts and uncertainties in the area of BSE and TSEs.

September

Q. What conclusion / recommendations did SEAC reach during its two day meeting in September 1998 regarding animal health?

A. The Committee reviewed the epidemiological data on feline spongiform encephalopathy. There are a relatively small number of cases in GB and SEAC confirmed that the epidemiological data is consistent with a food-borne source of infection. The Committee concluded that further epidemiological data should be initiated to learn more about TSE in cats. The Committee also considered and supported a proposal for further studies of cattle which were the offspring of BSE affected dams. The study would add to the understanding of the epidemiology of maternal transmission.

SEAC reviewed the proposals for disposal of excreta from experimentally infected cattle in the MAFF research programme (this issue was previously considered in January 1998). The Committee confirmed that 28 days following oral inoculation the excreta could be composted for a year and then safely used to fertilise arable land and the crops subsequently grown could in principle be used for both human and animal feed. Excreta from the first 28 days after challenge should be incinerated because if material from the oral inoculation were present in the faeces it would be during this period that the risk would be apparent.

In December 1997 the Committee considered the risks of spreading condensate from rendering plants on farmland and concluded the risks to human health were negligible. In September 1998 the Committee requested further information as to what went into the process which produced condensate before they could reach a conclusion about the safety of this practice with regard to grazing animals.

Q. What were the Committee’s discussions regarding human health issues?

A. The Committee discussed the possible risks of transmission of vCJD through medical procedures (iatrogenic transmission) consequent to the finding of abnormal prion protein in the appendix and tonsils of vCJD patients. The Committee agreed a summary of their discussions on reducing the risks of such transmissions would be made available to inform further consideration of this issue by the joint Advisory Committee on Dangerous Pathogens/SEAC subgroup which had been set up to look at decontamination procedures and related matters.

SEAC also considered a proposal to screen human lymphoid tissue, especially appendix and tonsils, for the presence of abnormal prion protein. The Committee stressed that any results, positive or negative, would need to be interpreted with great care. The presence of abnormal prion protein in lymphoid tissue would not necessarily indicate that the patient would later develop clinical neurological disease nor would it indicate the source.

Q. Why did SEAC meet with the Dormont committee in September 1998?

A. SEAC had previously met with the Dormont Committee (the French scientific committee on TSEs) in February 1997. Their meeting in September 1998 allowed for a broad exchange of information and views on CJD, BSE and scrapie in France and the UK. There was consensus between scientists on both Committees on aspects of the epidemiology, genetics, pathogenesis and transmission of these TSEs and the measures necessary to protect public health.

July

Q. What else did SEAC say about sheep and BSE?

A. The Committee again considered the theoretical possibility that BSE could exist in the UK sheep flock noting that no evidence of BSE in sheep in commercial UK flocks had so far been found. The Committee noted that limited experimental evidence which showed the clinical disease caused by inoculating sheep with BSE appeared to be very similar to the natural disease of sheep called scrapie. SEAC recognised that to distinguish the BSE strain from scrapie strains requires lengthy and expensive post mortem testing of sheep tissue but agreed that such work must continue. They also concluded that additional work was required to determine the extent of scrapie in UK sheep and set up a sub-group to develop further recommendations on this. They agreed that, at present, there was no need to recommend further action to protect public or animal health.

June

Q. What further advice, to that given in October 1997 on leucodepletion, did SEAC give in June 1998?

A. At its meeting in June 1998 SEAC reviewed the latest research and assessment of possible risks and noted that there was considerable uncertainty about whether or not the infectious agent may be present in human blood and, if present, to what extent it would represent any risk of transmission. The Committee recommended that Government should extend the use of leucodepletion for all blood destined for transfusion as soon as practically possible and that further research be carried out. They stressed that advice on such action was precautionary.

SEAC also reviewed the safety of beef in the light of these discussions and concluded that no further measures governing beef and beef products for human consumption were necessary.

April

Q. Why did SEAC have a a two day meeting in April 1998?

A. The majority of the two day meeting in April was devoted to a workshop to review the approaches, methodologies and current level of knowledge of key variables, which are central to the evaluation of risk to humans and animals from exposure to BSE. The Committee reviewed aspects of the possible risk of infectivity in milk. The discussions were informed by industry experts and scientists with expertise in the field. The Committee saw no reason to change their previous advice on the safety of milk. The Committee also noted recent research claiming to show that it was possible for rodents to retain experimental TSE infectivity without exhibiting signs of disease within their lifespan and approved research proposed to examine whether sub-clinical infection could be detected in cattle. At its next meeting in June 1998 SEAC reviewed a proposal for research into this area and concluded that this should be given high priority but noted that further refinements to the diagnostic tests and to the design of the possible studies were necessary.

March

Q. At their meeting in March 1998 SEAC reviewed an abstract of American research showing the scrapie infectivity had been detected in muscle in transgenic mice. What did they conclude?

A. The Committee noted that the mice in this experiment had been genetically engineered to artificially produce more of the normal PrP protein in muscle cells than in normal brain cells (PrP is the protein which adopts an abnormal conformation in TSEs). The Committee concluded that the results showed that the muscle cells have the potential to produce abnormal protein and that the assays which were in progress for infectivity in muscle of BSE infected cattle which did not involve a species barrier were important. The Committee also noted research in another neurological condition, idiopathic brainstem neuronal chromatolysis, which had potential to be confused with BSE on clinical grounds.

Q. What did SEAC say about openness?

A. The Committee, as part of a Government-wide initiative to increase the openness of advisory committees, discussed ways in which it could improve the transparency of its deliberations. SEAC welcomed moves to greater openness and expressed a willingness to participate in such moves. However, it was considered that a mechanism to safeguard confidential scientific, patient, veterinary and commercial information that was crucial to its work would need to be built into the process.

Q. SEAC discussed its previous advice on both human and bovine blood. What did the Committee say?

A. The Committee noted action being taken by Government following their previous advice on human blood. They considered that it was not necessary to add to or change previous advice at this stage but would review the situation when the risk assessment was complete. SEAC confirmed its previous advice on the use of bovine blood and saw no need to go beyond existing controls.

Q. What did SEAC say about Specified Risk Materials (SRMs) with regard to sheep and goats?

A. SEAC noted the latest position with Specified Risk Materials (SRMs) in the EU and the implementation of the SRM controls in the UK especially with regard to the controls on the spinal cord of sheep. They confirmed their previous advice; controls should prevent the use of sheep and goat vertebral column for production of mechanically recovered meat but production of tallow and gelatin, which involved a high degree of processing, could be permitted from sheep and goat vertebral column. The Committee also urged Government to pursue its plans for improving surveillance of scrapie in sheep and goats.

Q. What did the Committee say about the theoretical possibility that BSE infectivity could be present in cattle which do not show the signs of clinical disease during their normal life-span?

A. It was noted that such a situation had not been detected in the UK cattle population, however there was evidence from experiments in mice that in certain conditions the TSE agent can persist in the animal without ever causing clinical disease. SEAC explained that it would be important as the clinical disease in cattle declines to ensure that there is no such reservoir of latent infection and the Committee considered that Government should initiate further research on this issue.

SEAC views - February

Q. SEAC considered a preliminary analysis of the possible ways by which BSE infectivity may have entered the human food chain. What were the Committee’s views?

A. The Committee concurred with the point made in the summary of the preliminary analysis which states "There are many inputs to the study that are very uncertain, being based on judgement or limited data. Improvement would be desirable before decisions are made about public health implications of these results." The Committee also concluded that the preliminary analysis would not cause the Committee to call for changes to current measures to protect public health.

January

Q. What did SEAC say about the safety of milk at its meeting in January 1998?

A. The Committee reviewed the processing and use of milk in the light of recent research implicating lymphocytes in the pathogenesis of TSEs. The Committee noted that there was no evidence of infectivity in spleen or lymph nodes of cattle infected with BSE, that only low numbers of lymphocytes were left in milk after processing by the dairy and that the incidence of BSE in the UK continues to decline. SEAC agreed that no changes were necessary to previous advice issued on the safety of milk in April 1997 and July 1996 when the Committee found that there was no evidence from any of the transmissible spongiform encephalopathies that infectivity can be transmitted through milk

Q. Why were SEAC happy to allow the practice of feeding fishmeal to farmed fish?

A. The Committee considered this in January 1998 and concluded that the practice did not constitute intra-species recycling because there was more than one species involved and the material was not being sourced from farmed fish and therefore was not being re-cycled within the same population.

Q. What other conclusions did SEAC reach at its meeting in January meeting?

A. The Committee considered the use and disposal of bovine blood and concluded that there was no significant risk associated with the disposal of bovine blood on agricultural land. They saw no reason to change the advice issued in June 1996 when they saw no reason to recommend that the practice should be prohibited.

The Committee also considered options for disposal of animal excreta from experimentally infected cattle. They noted that for a period of one month all waste from animals orally challenged would be incinerated and agreed that other excreta could be composted and used as a fertiliser on agricultural land at the experimental farms concerned. They also recommended that detailed records of disposal should be kept.

The Committee discussed the use of bovine bone charcoal for water filtration. They noted that the sources of the bone were countries which had no reported cases of BSE and that production methods included heating to 1000° C. Consequently they concluded that the practice could continue since it represented no risk to human health from TSEs.

Other years: [2002] [2001] [2000] [1999] [1997] [1996/1997] [1996]

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