In a recent issue of the Canadian Sheep Federation’s ‘Points of View,’ a producer commented on the fact that atypical scrapie has shown up in New Zealand along with other countries throughout the world. This same producer wondered if the Canadian sheep industry, through genetic selection, is selecting sheep that may be susceptible to atypical scrapie.
I’d like to take the opportunity to follow up on these comments and provide some further information on atypical scrapie.
Atypical scrapie (also known as Nor 98) is a distinct brain condition in sheep and goats that is completely unrelated to classical scrapie.
The evolving international scientific view on Nor 98 is that it is a spontaneously occurring degenerative brain condition in older sheep and goats.
Nor 98 differs from classical scrapie in its clinical, neuropathological and biochemical features. Most cases have been detected in apparently healthy sheep by post-mortem examination during routine slaughter in European sheep.
The United Kingdom Spongiform Encephalopathy Advisory Committee (SEAC) has concluded that, “On the basis of a number of characteristics, Nor 98 can reliably be distinguished from classical scrapie.” Their statement goes on to say, “on the basis of emerging data, it may be more appropriate to consider atypical scrapie as a distinct Transmissible Spongiform Encephalopathy (TSE) of small ruminants and not simply a variant of what is now called scrapie.”
Nor 98 has been found in a number of countries since it was first identified in Norway in 1998. It has been found at very low incidence rates – approximately one in 1,000 sheep tested.
The Canadian Food Inspection Agency reports six cases of Nor 98 in Canada since 2007.
In October 2009, it was reported that a sheep originating from New Zealand (a certified scrapie free country) had been tested positive for Nor 98. Reports on the incident state that “a single New Zealand sheep brain (which had been sent to Europe as part of a program providing brains to assist the EU in developing testing for scrapie) tested positive for Nor 98. This is indicative that the condition is present in New Zealand and is expected to be at a similar prevalence to other countries where it has been detected. International evidence shows every country that has specifically tested its sheep for the condition has found it.”
Because Nor 98 has been internationally recognized as a separate disease from classical scrapie, New Zealand’s livestock populations remain internationally recognized as scrapie free.
There is scientific consensus, including that from Health Canada, that there are no associated human health concerns or food safety issues from Nor 98.
When it comes to genotyping and genetic selection, there is no established genetic susceptibility or resistance to Nor 98. It has been found that some animals which were positive for atypical scrapie had genotypes identified as resistant to classical scrapie.
There is some association with phenylalanine (F) at codon 141 and histidine (H) at codon 154 in cases of Nor 98, but further research is needed to establish if there is genetic susceptibility or resistance to Nor 98.
The Canadian Sheep Federation’s scrapie projects are funded by Agriculture and Agri-Food Canada’s (AAFC) Agricultural Flexibility program. Agriculture and Agri-Food Canada (AAFC) is committed to working with industry partners. Opinions expressed in this document are those of the CSF and not necessarily those of AAFC.