Opinion of the Scientific Panel on biological hazards (BIOHAZ) on the assessment of the age limit in cattle for the removal of certain Specified Risk Materials (SRM)

No abstract available

The European Food Safety Authority (EFSA) was invited by the European Commission to review the previous scientific opinions (Scientific Steering Committee, SSC) on the age limit for the removal of certain bovine tissues as specified risk material (SRM) taking into account a report from the referred OIE-consultation group of experts and additional information.

The assessment of the exclusion of certain SRM at a certain age limit is based on available data of ongoing experimental pathogenesis and dose/incubation period studies and on knowledge of the epidemiology of BSE with respect to age at infection and age at detection by clinical and active surveillance.

On the basis of pathogenesis studies results it can be assumed that in CNS the likely detectable PrPSc, and consequently the likely detectable infectivity appears at about ¾ of the incubation time. Based on the earliest clinical manifestation seen in pathogenesis studies and assuming that the last quarter of the incubation period would be positive for infectivity, the earliest infectivity would have to be assumed at 26 months. However, this would reflect uptake of the BSE agent via the gut only. Other modes of prion uptake, e.g. via the oral mucosa and neural spread, cannot be completely excluded and theoretically might significantly shorten the incubation time. However, there are no observational data at present to support this. As for tonsil and intestine, there is no scientific basis to raise the age limit for their removal.

From the analysis of the epidemiological data, it is observed that the average age of BSE positive cases reported in the EU has been increasing from 86 to 108 months over the period 2001-2004, most likely due to effective control measures. It is further observed that the number of BSE cases reported at an age less than 35 months in past years in the EU has been only 4 out of a total number of 6520 BSE cases on a total of close to 41 million animals tested. The minimum age of BSE cases in EU has been 28 and 29 months (2 animals) in 2001, 32 and 34 months in 2002, 36 months in 2003 and 42 months in 2004. The three youngest animals were emergency slaughter, whereas the remainder of BSE cases in young animals (i.e. younger then 48 months, table 1) included all target groups.

If the cautious approach of the former SSC is followed and the minimum age is taken as the denominator for the age at which SRM are to be removed, then a cut-off at 30 months would not cover such young animals if assuming ¾ of the incubation period for the appearance of infectivity in CNS. A cut-off at 21 months would cover the last quarter of incubation time of even the single youngest animal observed since the start of the EU surveillance in 2001.

If the BSE cases in very young animals are not taken into account and the mean age at which BSE is detected in the field is taken as the denominator, then a cut-off at 30 months would represent a considerable but not an absolute safety margin with respect to detectable BSE infectivity.

Present BSE surveillance appears to be equally effective in the EU member states. Nevertheless, there could be important differences between EU Member States according to differences in culling rates and other factors like stage in the epidemic.

BSE, specified risk materials, cattle, age, epidemiology.