Along with other EU member states, the UK was required to establish a surveillance programme for sheep scrapie in 2002. The target was to examine 60,000 sheep, aged over 18 months and destined for human consumption and 6,000 fallen stock. This resulted in the Regional Laboratories being inundated with sheep heads in the last few months of the year. The tolerance and ingenuity of VLA staff involved ensured we came very close to our target number of abattoir sheep.
The fallen stock survey was not so successful as farmers were only able to submit a fraction of the numbers of carcases required. In contrast the survey of cattle for BSE, having been established in 2001, was almost routine.

BSE Testing at VLA Newcastle

The VLA Epidemiology team was heavily involved in the Food Standards Agency (FSA) deliberations on the future of the Over Thirty Months Scheme (OTMS), by being members of their Risk Assessment Group. In particular they modelled the likely increase in exposure risk to consumers if the OTMS was abandoned or changed. An important factor taken into account was the identification of approximately 40 BSE cases born after 1 August 1996, the date from which the UK feed controls are considered to have reached their maximum efficiency. Investigations continue into potential routes of infection, but all the evidence suggests that they cannot be attributed to maternal transmission.
A small survey of approximately 300 fixed samples of brain tissue from deer looking for evidence of infection with TSEs using immunocytochemistry (ICC) was completed during the year.

No cases were found, but test methods have been shown to be valid and warrant the expansion of the survey next year.
A report on the deer industry in Great Britain was commissioned as an aid to future surveillance planning.

Western Blot Technique used on the sheep scrapie survey

The programme of experimental challenges of cattle and sheep continued with a number of preliminary but potentially key results reported to the Spongiform Encephalopathy Advisory Committee (SEAC). A study that attempted to determine the minimum oral dose required to infect calves progressed to the point of confirmation of disease in the first four animals, one each in groups dosed with 1 or 0.01g, and two in the 0.1g challenge group. The time between infection and death ranged from 56 to 59 months. Susceptibility to such low doses highlights the difficulties of preventing food-borne exposure, especially by cross contamination on farm or in transit and where testing of the feed for contaminants may not detect the error.

In a further study in which cattle had been inoculated with tissues from experimentally infected cattle, transmission was demonstrated to one animal inoculated with palatine tonsil collected 10 months after oral exposure. A parallel study in which nictitating membrane from a group of naturally infected animals was inoculated resulted in transmission to one of five challenged cattle. This was an unexpected result.

Recovering samples from the TSE archive

Strain typing is now a large component of the TSE programme, either using the traditional method of mouse inoculation, or with complementary molecular methods using ICC and western immunoblotting. Further work using the two molecular methods has so far confirmed a consistent ‘phenotype’ for experimental BSE in sheep, which is reassuring as the methods are being used routinely for statutory diagnosis. Another year has generated a vast amount of data within the mouse strain-typing programme and IT developments have helped in the handling and manipulation of the raw data. A further series of sub-passages has increased confidence in methodologies. This is important as VLA, the Community Reference Laboratory, is expected to translate opinions of the EU Scientific Steering Committee into working instructions for all National Reference Laboratories. This work will also incorporate an evaluation of the molecular methods of strain characterisation.

Last but not least, mention must be made of the TSE Archive, a resource that will be central to our and EU Community research for many years to come. It was initially set up in 1996 and established as a discrete Unit in 2002. An early target for the Unit was ISO9001 certification and this was achieved in 2003; a tremendous effort. In addition, after a long gestation period, the Independent Archive Advisory Group was established to peer review the archiving strategy on behalf of Defra and VLA, and to sanction release of tissues to applicants.