Use of immunodiagnostic tests on an outbreak of scrapie in Latxa sheep: Pathogenetic and epidemiologic implications

Ascrapie outbreakwas detected in the year 2003 in a flock of 222 black-faced Latxa sheep when two suspect animals were submitted for laboratory diagnosis. After the two index cases were confirmed as scrapie positive by rapid tests and immunohistochemistry (IHC), two new clinical cases were recognized in the ante-mortem inspection during the flock destruction. Of the remaining 218 animals, 16 sheep were also positive to at least one of the rapid tests and IHC, and 6 more were negative by all rapid tests but positive by IHC in lymphoid and/or peripheral nervous tissues but not in central nervous system (CNS) tissues. Ten different genotypes were found in the flock, and, as expected, most of the positive sheep were of the ARQ/ARQ genotype (21/26, 80.7%), which was the most prevalent genotype in this flock and also in Latxa breed. In total, 26 positive ewes were identified in a flock with only 4 clinical cases (clinical/subclinical ratio of 1:5.5) indicating that the prevalence of infection in a positive flock might be considerably higher than clinical data indicates. The implications of the different patterns of PrPSc deposition in the pathogenesis and dissemination of scrapie within the host are discussed. © 2006 Elsevier B.V. All rights reserved.