Abstract
BackgroundAtypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Retrospective studies have identified cases predating the initial identification of this form of scrapie, and epidemiological studies have indicated that it does not conform to the behaviour of an infectious disease, giving rise to the hypothesis that it represents spontaneous disease.However, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation in transgenic mice and sheep. The first successful challenge of a sheep with 'field' atypical scrapie from an homologous donor sheep was reported in 2007.ResultsThis study demonstrates that atypical scrapie has distinct clinical, pathological and biochemical characteristics which are maintained on transmission and sub-passage, and which are distinct from other strains of transmissible spongiform encephalopathies in the same host genotype.ConclusionsAtypical scrapie is consistently transmissible within AHQ homozygous sheep, and the disease phenotype is preserved on sub-passage.
Highlights
Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries
Atypical scrapie does not coexist with classical scrapie, some field cases originate from flocks which have reported classical scrapie, and it has occurred in a closed research flock with endemic classical disease [9]
In addition to the AHQ/AHQ animals intracerebrally challenged with atypical scrapie, data is presented on the experimental classical scrapie positive control animals which were intracerebrally challenged
Summary
Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Atypical scrapie does not coexist with classical scrapie (e.g. on individual farms, and at a national level, such as in Portugal and the Falkland Islands [8]), some field cases originate from flocks which have reported classical scrapie, and it has occurred in a closed research flock with endemic classical disease [9]. It has been reported in a research flock in which detailed biosecurity measures have been maintained, founded with sheep from a country free of classical scrapie [10]. Despite lack of evidence for infectivity in the epidemiological data, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation into ovinised transgenic mice [12] and sheep [13]
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