TSE infectivity model (TSEi) in animal tissues: Bovine intestines and mesenteries
A stochastic quantitative risk assessment (QRA) has been developed to (1) compare the level of infectivity of different TSE agents in animal tissues, (2) estimate the impact of amendments to the list/age for the removal of SRM on residual TSE infectivity levels for a single infected animal and at the country level per year, and (3) estimate the impact of certain processing technologies on residual TSE infectivity in selected animal tissues or products. In this report the QRA is focused on bovine intestines and mesentery. The tissue types identified for quantitative modelling are: ileum, duodenum, jejunum, caecum, colon, mesenteric lymph nodes, mesenteric nerves and the celiac and mesenteric ganglion complex (CMGC). Of these tissues processed products include bovine intestines (duodenum, jejunum, caecum, and colon) used to produce sausage casings and the rendering of fats from mesentery tissues. The ileum is not processed for human consumption. This report describes the model approach taken together with the parameterization for each tissue type conceptually divided into five different components: surveillance, abattoir, SRM, processing, and infectivity. Both uncertainty and variability associated with input data have been included separately in the model where estimates are known. A baseline model has been completed using surveillance and demographic data from 2012. Two case studies are also provided, the retrospective analysis of the estimated amount of infectivity in the healthy slaughter and emergency slaughter streams by age at slaughter (2007-2011), and the amount of infectivity accumulating during a theoretical re-emergence of BSE. Results are provided based on the current parameterization and include associated quantifiable uncertainty and variability. When developing the risk assessment a number of assumptions were made which need to be considered when reviewing results.