Using an epidemiological framework and bovine spongiform encephalopathy investigation questionnaire to investigate suspect bovine spongiform encephalopathy cases: an example from a bovine spongiform encephalopathy case in Ireland in 2015

O’Connor, Jarlath T; Byrne, Justin P; More, Simon J; Blake, Martin; McGrath, Guy; Tratalos, Jamie A; Mcelroy, Maire C; Kiernan, Paul; Canty, Mary J; O’Brien-Lynch, Chris; Griffin, John M

Although widely accepted as the main source of BSE prion transmission for cases of classical BSE, there was no evidence in this case to indicate that the feed supply chain was a contributory factor, or that the case animal had been fed with feed containing MBM. As well as carrying out a thorough investigation of the feed supply chain for the index herd, the investigation team evaluated the potential for contaminated feed to have been supplied to the farm. In 2009 and 2010, few BSE cases were detected in Ireland (9 in 2009, 2 in 2010) compared with a high of 333 in 2002. Also, comprehensive control measures had been put in place in 2009 and 2010, including active and passive surveillance, removal and destruction of dead-on-farm animals, effective rendering systems, and controls with regard to the potential for cross-contamination at mills. Feed imported into Ireland was also subject to routine inspection and testing, which did not identify any bone spicules. These controls led to a substantial reduction in the likelihood of contaminated feed acting as a source of the BSE agent. However, because of the passage of time, it was not possible to be certain that we obtained complete information on all possible sources of contamination of feed for the index herd. It has been shown that an animal can be infected by a very low oral dose of the BSE prion, with the attack rate and incubation period dependent on the dose. 46 47 Findings in the UK have highlighted the possibility of persistence of traces of contaminated feed in on-farm feed stores and the need for special care in the cleaning and maintenance of feed bins and silos and other feed storage facilities. 36 Consequently, inadvertent exposure to the BSE agent in residues of old particles of feed cannot be definitively ruled out.