IFST updated Information Statement on BSE and Variant Creutzfeldt-Jakob Disease (vCJD)
Bovine Spongiform Encephalopathy (BSE) and Variant Creutzfeldt-Jakob Disease (vCJD) In Humans
The Institute of Food Science & Technology, through its Public Affairs and Technical & Legislative Committees, has authorised the following Information Statement, dated October 2004, replacing the Statement of October 2001 and any previous version.
This updated Information Statement takes account of available data and published research up to September 2004. As with the previous update, in order to accommodate much new material without extending the length, some of the earlier material which has become of historical rather than of current interest has been eliminated or curtailed, but literature references from that period that remain relevant have been retained.
BSE background: An outline is given of the background to BSE, its origin and transmission in cattle. While there is strong evidence that the cause of the UK BSE epidemic was the feeding of infected meat and bone meal (MBM) to cattle, it will probably never be proved or provable whether the infection originated from MBM made from scrapie infected sheep or from MBM made from a hypothetical cow with a rare sporadic TSE.
BSE incidence: The continued dramatic year-on-year fall in the number of new clinical cases of BSE in Great Britain (from the peak of 36,680 in 1992, to 1,311 in 2000, is as was forecast and on track to bring the epidemic to an end. Note that data for subsequent years (781 in 2001, 445 in 2002, 174 in 2003) are not strictly comparable with earlier data because the large number of UK cattle killed and either buried or incinerated on pyres during the 2001 UK foot and mouth disease outbreak must have included an unknown number incubating BSE. In addition to a total of 179,093 clinical cases (passive surveillance), active surveillance post-mortem testing since 1999 has revealed a total of 1,514 cases (to 7 September 2004) and 3,295 cases (to 9 September 2004) in the rest of the world, in apparently healthy cattle, the latter most likely resulting from feeding to cattle UK mammalian MBM imported as pig and poultry feed prior to 1996. It is possible that cases may emerge in other countries which imported this material. WHO has stated that over 100 countries are at risk. The EU Commission publishes an updated table of incidence in EU countries, and the OIE maintains an updated world list, by countries.
The infective agent in transmissible spongiform encephalopathies: Evidence continues to mount in support of the prion hypothesis, as does the body of research consistent with it and inconsistent with other hypotheses. Strong confirmation has been offered by separate lines of research demonstrating conversion of normal cellular prion protein to the infective form. This does not preclude the influence or “triggering” effect of other factors. The role of copper and zinc ions in prion conformation has been demonstrated and the possible role of manganese in change of conformation has been mooted. Two lines of research have also shown that multiple prion strains are compatible with the prion hypothesis.
Prion infectivity and transmission mode: Although research indicates that the lymph system plays an important part in the transmission of infectivity to the central nervous system (CNS) the exact mechanisms by which this occurs are insufficiently understood.
Infectivity of bovine materials: Links to a series of Opinions by the EU Scientific Steering Committee on the infectivity of various bovine materials derived from BSE-infected cattle may be found at http://europa.eu.int/comm/food/fs/bse/scientific_advice08_en.html
Ø Beef, milk and bones: Mouse assay tests have not detected BSE infectivity in muscle meat (beef) or milk from confirmed BSE cows. It is not yet known if beef or milk from BSE-infected cows contain amounts of BSE infectivity too small to be detected by mouse assay. The results of assay experiments in cattle will not be known until 2007. Current risk from beef or milk is considered to be extremely small. Experiments have detected infectivity in the dorsal root ganglia, the trigeminal ganglia and the bone marrow. In regard to the latter, risk assessment indicated that the added risk involved to people eating beef is extremely low, about one new case of new variant CJD in a billion years per person. However the risk estimate has a wide range of uncertainty. The then UK Government responded by banning the sale of bone-in beef, but the ban was eventually lifted.
Ø Mechanically recovered meat (MRM): Attention has focused on MRM as a probable source of high titre infectivity in the food chain, particularly prior to 1995 when the UK use of spinal column for MRM was banned. Many years later an intuitive supposition was mooted that cheap meat products more likely to contain MRM had been consumed much more in Scotland and the North of England than in the South could explain the significantly greater incidence of vCJD in the former than the latter. Though the supposition appeared, on examination of consumption statistics, to be erroneous, nevertheless it gave rise to two projects retrospectively attempting to determine quantitative MRM usage in various meat products in the earlier period. Current EU measures prohibit MRM from any bovine or ovine bones.
Ø Gelatin and tallow: In its updated reports, the EU Scientific Steering Committee carried out risk assessments of various raw materials and production processes for gelatin (March 2003) and tallow (April 2003)respectively.
Ø Blood: Although infectivity had not been found by mouse assay in blood of BSE-infected cattle, in September 2003 the EU Scientific Steering Committee issued an updated Opinion taking account of the implications of the then recent papers on transmission of BSE by blood transfusion in sheep.
Early UK controls
The early measures in the UK for control of the epidemic in cattle were:
Ø to slaughter and destroy animals clinically diagnosed on the farm or elsewhere (from 1988);
Ø to prohibit the feeding of material containing animal protein derived from ruminants to cattle and other ruminants (1988):
Ø to prohibit Specified Bovine Offals (SBOs) from the food or feed chain
The first and third of these served, of course, also as part of the precautionary programme of measures to protect human health, in case transmissibility to humans might occur.
UK controls from mid-1996: From August 1996 strict enforcement of the ban on mammalian MBM for all farm animals, exclusion of SRMs from the food chain, and slaughter of cattle aged over 30 months (the OTMS) plus a cattle traceability scheme led to the lifting in November 1998 of the EU-imposed global ban on British beef exports, on the basis of the monitored enforcement of the existing UK controls plus fulfillment of the requirements of the Florence Agreement by the Date-Based Export Scheme (DBES) and cull of offspring born on or after 1 August 1996 to BSE-infected dams.
During 2000, the FSA held a series of open “Stakeholders Meetings” at which a thorough review was carried out of the BSE controls [Specific Risk Materials (SRMs), the MBM ban and the Over Thirty Months Scheme (OTMS)] resulting in recommendations to the Prime Minister, which were accepted, for the retention, strengthening and enforcement of the controls. In 2004, with the testing at slaughter of all cattle over 28 months, the value of the OTMS has been reviewed.
BSE controls across the EU: In December 2000, the EU Council of Ministers decided on new controls across the EU Member States, essentially similar to the UK controls referred to above, but with post-mortem testing of suspect castle over 30 months from January 2001 and of all over 30 months cattle, and some categories of over 24 months cattle from 1 July 2001. Tests are mostly being carried out by the Prionics or Bio-Rad methods. From January 2001 to end of May 2001, EU Member States had tested over 2.4 million apparently healthy cattle, mainly aged over 30 months, of which 90 were found positive for BSE. Prior to 1 July 2001 testing was not carried out in the UK because under the OTMS provisions such cattle are slaughtered and not permitted to enter the food chain. From 1 July, the UK began testing of some categories and later extended the testing. On 7 February 2001, the European Commission agreed three proposals: to require the removal of the vertebral column from all cattle over 12 months and to prohibit mechanically recovered meat from bones of ruminants; new requirements to pressure-cook rendered animal fats from ruminants for food and feed; and authorising certain hydrolysed proteins from fish and feathers.
Diagnostic tests: The EU Commission has approved five rapid postmortem methods for testing for BSE in cattle and ten more are under evaluation. A number of possible ante mortem tests have been proposed for cattle and for humans but so far none has been officially accepted. A problem of any ante mortem method is lack of knowledge of the stage of incubation at which infectivity is detectable.
BSE developments outside Europe: The occurrence of the first of (now) 11 cases of BSE in Japan in September 2001, a single case in Canada in January 2003 and a single case (of Canadian origin) in USA in December 2003, has led to new concerns and a range of new measures in those countries.
BSE risk by countries or regions: The EU Scientific Steering Committee has issued a series of Reports giving its opinion on the geographical BSE risk (GBR) together with detailed assessment reports for various countries. GBR is not an indicator of a risk to humans via food consumption, but a qualitative indicator of the risk that live cattle could be infected with the BSE agent and incubating the disease. The analysis is based on a qualitative model developed by the SSC that was applied to information provided voluntarily by these countries. Among major considerations are whether live cattle or MBM have been imported from what were at the time high risk countries, especially the UK, and the time and effectiveness of risk management measures. Countries were assessed in four Categories:
Ø Category I: Highly unlikely to present a BSE risk
Ø Category II: Unlikely, but a BSE risk cannot be excluded
Ø Category III: Likely to present a BSE risk, even if not confirmed, or presenting a low level of confirmed BSE risk
Ø Category IV: BSE risk confirmed at a high level
In August 2004 the European Food Safety Authority (EFSA) issued reports of reassessment of some countries.
Vertical transmission of BSE? The EU Scientific Steering Committee at its meeting of 18-19 March 1999 adopted an “Opinion on the possible vertical transmission of Bovine spongiform encephalopathy (BSE)” (amended May 2002). Subsequent research gives no support to the occurrence of vertical transmission.
BASE: Atypical cases of BSE in individual cattle have been found in Japan, France, Italy, the Netherlands, Belgium, Denmark and Poland. This appears to be a second cattle TSE which has been named bovine amyloidotic spongiform encephalopathy (BASE).
BSE in sheep? Fears that BSE may be present in sheep but masked by scrapie led to precautionary legislation in August 1996 (updated and extended in April 2002) to exclude from the food chain sheep (and goat) tissues corresponding to Specified Bovine Materials. There is no evidence of presence, but if it is present, and behaves in sheep like scrapie, it could involve far more tissues being infected than in cattle, both vertical and horizontal transmission, and infection of pastures. There is as yet no rapid test to distinguish BSE from scrapie in sheep. The full extent of scrapie in EU flocks is unknown. On 2 June 2004 DEFRA issued a consultation document on “Contingency plan for the emergence of naturally occurring BSE in sheep”.
BSE in primates: Examination of the pattern of prion distribution and brain degeneration in 20 euthanised lemurs from three different French primate centres, all of whom had been fed beef protein dietary supplements, was virtually identical to that seen in experimentally infected lemurs. The results suggest that BSE infection of zoo and breeding centre primates may have been more widespread than previously thought
BSE/vCJD: From research published from October 1996 onwards, scientific evidence has been accumulating that BSE infectivity and variant CJD (vCJD) infectivity carry the same "fingerprint". Although the scientific evidence does not prove a causal connection, the evidence is consistent with the transmissibility of BSE infectivity to at least some humans (possibly to all humans but at varying incubation rates); and taken in conjunction with related circumstances it increases the likelihood of a causal connection. It is theoretically possible that both BSE and vCJD may have been triggered by some third presently unsuspected cause, but it is difficult to conceive what that might be. On 28 September 2001, the UK Department of Health announced a £55 million compensation package for families of vCJD victims.
vCJD incidence: The UK Department of Health News Release of 6 September 2004, gives a cumulative total number of definite and probable cases of vCJD to date as 149 (including 5 who are still alive). There are fifteen definite and probable cases outside the UK, three of whom have had UK connections. Assuming the likelihood that most cases of vCJD so far are the result of having consumed BSE infective materials, mainly prior to 1989, however, although attempts have been made to estimate minimum and maximum figures (widely apart) it is still not possible to draw from the figures to date any long-term conclusions, whether optimistic or pessimistic, as to likely future incidence. Although the present “wave” is showing a significant decline since the peak in 2002, and some have tried to draw optimistic conclusions from this, research indicates there may be more “waves” to come, plus cases from transfusion of blood from infected donors or from the use of infected surgical instruments.
Tonsil biopsy survey: Tonsil biopsy has been shown to obviate the need for brain biopsy for ante mortem diagnosis of vCJD. In a testing of 12,674 samples of (mainly) appendicectomies and some tonsillectomies, three appendicectomy samples showed lymphoreticular accumulation of prions, giving a estimated prevalence of 237 per million (95% CI 49-692 per million). The pattern of lymphoreticular accumulation in two of these samples was dissimilar from that seen in known cases of vCJD. A much larger test, of tonsils from 100,000 patients, may give a better picture.
Blood (human): Research reports, including the finding of infectivity in the tonsils of vCJD victims, and evidence showing that the lymph system is involved in passage of infectivity from gut to brain, implicate the lymphoreticular system, and suggest the possibility that circulating lymphocytes in the blood may carry infectivity. This led to adoption of the leucodepletion of blood supplies in November 1997 as a precautionary measure. However, research has now suggested that leucodepletion removes only 42% of the initial TSE infectivity from whole blood. While further work is needed to identify the location of the residual infectivity, it was presumed that it is plasma associated.
Following a case in December 2003 of vCJD possibly acquired by a 1999 blood transfusion, a second case of possible transmission of vCJD from person to person via a 1999 blood transfusion was reported [Peden, AH et al, (2004) A patient in the UK received a blood transfusion in 1999 from a donor who later went on to develop vCJD. The patient died of causes unrelated to vCJD but a post mortem revealed the presence of vCJD infectivity in the patient’s spleen. This was the first instance of vCJD in a person in the codon 129 heterozygous (met/val) group.
Therapeutic/prophylactic agents? Prusiner’s group (Korth et al (2001) have reported that tricyclic derivatives of acridine and phenothiazine exhibit half-maximal inhibition of PrPSc formation at effective concentrations (EC50) between 0.3 µM and 3 µM in cultured cells chronically infected with prions. Because quinacrine and chlorpromazine have been used in humans for many years as antimalarial and antipsychotic drugs, respectively, and are known to pass the blood-brain barrier, they suggest that they are immediate candidates for the treatment of CJD and other prion diseases. However, following media reports in August 2001 that two vCJD victims have been treated and that one has shown remission, Prusiner has stated (10 October 2001) that one has died and the other has become worse. However, In August 2004 the UK Medical Research Council is officially launching the "PRION-1" trial, a trial of potential treatments. After four years of debate over which to test, it will focus on quinacrine, The National Prion Disease Clinic at St Mary’s Hospital in London has already given the drug to around 20 patients, but the results are not yet published.
Also from within Prusiner’s group comes a report that several antibodies cleared prion clumps out of cultured mouse brain cells. seeming to interrupt the conversion of normal prions by malignant ones.
There is some scientific evidence that compounds in the pentosan polysulphate (PPS) group might have potential for use as prophylactic agents against vCJD in humans. In the absence of further data on efficacy and safety, SEAC and the UK Department of Health did not consider that it was justified to recommend the wide use of PPS as a possible prophylactic against vCJD. In certain circumstances, where there is a tangible risk as a consequence of direct exposure to infectivity (such as an accident in a laboratory), there might be a case for administration of PPS. However, in June 2003 it was reported that, after the father of a vCJD victim at an advanced stage took the hospital concerned to court and after several months the court decided that the operation should go ahead, treatment with PPS had an unexpectedly beneficial result.
Official Inquiry into BSE and CJD: IFST welcomed the announcement of the official independent inquiry into BSE, its terms of reference and the open way in which it was to be conducted. IFST made a written submission to the Inquiry.
The Final Report, evidence and witness statements all appear on the BSE Inquiry Web site http://www.bseinquiry.gov.uk/
The Inquiry Report, dealing with UK events up to 1996, identified problems of excessive Government secrecy and unjustified public reassurances; inadequate communication among Government Departments; inadequate handling of hazard and uncertainty; lack of foresight that BSE might cause vCJD and of planning for that eventuality, lack of correct use of scientific advisory committees; ineffective enforcement of the control measures; inadequate coordination of research. Measures since March 1996, and not least the creation of the Food Standards Agency, have gone a long way to rectifying these deficiencies. The UK Government’s final ’Response to the Report of the BSE Inquiry’
http://www.defra.gov.uk/animalh/bse/general/response.pdf was published on 28 September 2001.
Much still remains unknown: The following are among the principal gaps in scientific knowledge to date:
Ø There is no treatment or cure for BSE or vCJD;
Ø As previously indicated, although research is giving increasing evidence of pathogenesis pathways the exact mechanisms of transmission of infectivity to the central nervous system are insufficiently understood;
Ø There is no rapid ante-mortem diagnostic test for BSE or vCJD;
Ø It is not known at what stage of incubation a BSE-incubating cow gives a positive result in a post-mortem test or would give a positive result in an ante-mortem test if one existed;
Ø It is not known yet whether muscle meat or milk carry infectivity at too low a level to be measured or detected by existing methods;
Ø it is not known whether BSE exists in the sheep flock;
Ø Assuming a causal relationship between vCJD and oral consumption of BSE infectivity, it is not known what is the infective dose, or whether it is a single dose or cumulative;
Research needs: The foregoing areas where knowledge is lacking or inadequate clearly indicate the priority needs for research to fill those gaps.
Every successive update of this Information Statement has emphasised
"While that sums up the present state of knowledge, scientists always have to keep open minds. They have to act on existing knowledge while recognising that further research will bring new information and knowledge, which may in turn lead to revised conclusions. We welcome the devotion of substantial extra resources to research in this field."
To read the full text (68 pages) visit http://www.ifst.org/hottop5.htm
Glossary of abbreviations
BAB – (cattle) born after the ban (on ruminant feed for ruminants)
BARB – born after the reinforced or “real”) ban in August 1996
BSE – bovine spongiform encephalopathy
CFIA – Canadian Food Inspection Agency
CJD – Creutzfeldt-Jakob disease
CJDSU – CJD Surveillance Unit
CTS – cattle traceability scheme
CVL – Central Veterinary Laboratory (now the Veterinary Laboratory Agency)
DBES – Date-Based Export Scheme
DEFRA – UK Department for Environment, Food and Rural Affairs
DoH – UK Department of Health
EFSA – European Food Safety Authority
FMD – foot and mouth disease
FDA – US Food and Drug Administration
FSA – UK Food Standards Agency
HPA – Health Protection Agency
i/c – intra-cerebral
MAFF – former UK Ministry of Agriculture, Fisheries and Food
MBM – meat and bone meal
MRM – mechanically recovered meat
OIE – World Organisation for Animal Health
OTMS – Over Thirty Month Scheme
PrP – prion protein
PrPc – normal cellular prion protein
PrPsc – (Infective) prion
SEAC – Spongiform Encephalopathy Advisory Committee
SBO – Specified Bovine Offal
SBM – Specified Bovine Material
SRM – Specified Risk Material
TSE – transmissible spongiform encephalopathy
nvCJD – new variant CJD, term used by CJDSU in 1996 to describe the original ten cases
vCJD – alternative for (new) variant CJD. (Note: At its meeting on 18 March 1999, (SEAC) agreed that “vCJD” should be used in preference to “nvCJD” in line with current practice in many scientific journals. Although this designation has been a subject of criticism on the grounds that it implies only one “variant”, for consistency “vCJD” is used throughout this Information Statement, even when quoting papers or statements in which “nvCJD” was used).
USDA – US Department of Agriculture
VLA – Veterinary Laboratory Agency (formerly Central Laboratory Agency)
Ralph Blanchfield | alfa