Estimating the impact on food and edible materials of changing scrapie control measures: The scrapie control model

Abstract

Multiple controls established during the bovine spongiform encephalopathy (BSE) epidemic were not solely applied to BSE in cattle, but were implemented for scrapie in sheep and goats due to concerns over the occurrence of BSE in sheep. In the absence of BSE in sheep being observed, control measures for prion diseases are now being evaluated to ensure they remain proportionate to risk. This risk assessment, aims to estimate, by use of stochastic simulation, the impact of reducing controls for Specified Risk Materials (SRM) from sheep at abattoir. Three scenarios have been included: 1) current list of SRM; 2) brain and spinal cord of adult sheep; and 3) the brain of adult sheep. Results indicate the total amount of infectivity passing through British abattoirs is highest for atypical scrapie with nearly 3,500,000 Ovine Oral (OO) ID per year. The majority of this infectivity enters Category 1 waste for incineration, with only 13,000 OO ID per year within edible products. Under Scenario 2, an additional 4000 OO ID per year would be classified as edible products from the lifting of restrictions on the distal ileum of adult sheep. However, if SRM removal was limited to brain, an additional 110,000 OO ID per year would be permitted into edible products with the lifting of restrictions on the spinal cord of adult sheep. For classical scrapie, there is a mean estimate of infectivity of 30,000 OO ID per year at abattoir. This is lower than for atypical scrapie due to the lower occurrence of this disease in Great Britain. However, more infectivity is destined to reach the food chain as the disease is peripherally distributed in the carcase. The highest contributor to the total amount of infectivity consumed per year is the intestines (duodenum and jejunum). If SRM removal is limited to the brain and spinal cord of sheep over 12 months of age, there is an approximate mean increase from 19,000 to 21,000 OO ID per year diverted to edible products. If the SRM list is restricted to brain only, this increases to over 23,000 OO ID per year. For the potential of sheep-BSE, there is a very low estimate of 29 OO ID per year in total from carcases entering abattoir, due to the potential very rare occurrence of this disease. Given changes in SRM regulations there is a change of an additional 4 OO ID per year being diverted to edible products.

Scientific report on the analysis of the 2‐year compulsory intensified monitoring of atypical scrapie

“…Unlike CS, PrP Sc has never been demonstrated in the peripheral tissues in AS cases, but low levels of infectivity can still be present in skeletal muscle, peripheral nerves and lymphoid tissues of affected animals. It has been estimated that the total amount of AS infectivity passing through British abattoirs to the food chain is nearly 3,500,000 Ovine Oral (OO) ID50 per year (Adkin et al., 2018 ).…”

Annual Report of the Scientific Network on BSE‐TSE 2018

“…This equates to a 10 fold increase in BOID 50 but the amount is still small due to the very low likelihood of infected animals being present in the 2017 healthy slaughter population. The same model was applied by Adkin et al (2018) to assess the impact of the removal of Specified Risk Materials (SRM) from sheep on potential prion infectivity passed into the food and protein material chains. For classical scrapie, there is a mean estimate of infectivity of 30,000 Ovine Oral (OO)ID 50 per year at abattoir, lower than for atypical scrapie (3,500,000 OOID 50 per year) due to the lower occurrence of this disease in Great Britain.…”