Ovine progressive pneumonia provirus levels are unaffected by the prion 171R allele in an Idaho sheep flock

Abstract

Selective breeding of sheep for arginine (R) at prion gene (PRNP) codon 171 confers resistance to classical scrapie. However, other effects of 171R selection are uncertain. Ovine progressive pneumonia/Maedi-Visna virus (OPPV) may infect up to 66% of a flock thus any affect of 171R selection on OPPV susceptibility or disease progression could have major impact on the sheep industry. Hypotheses that the PRNP 171R allele is 1) associated with the presence of OPPV provirus and 2) associated with higher provirus levels were tested in an Idaho ewe flock. OPPV provirus was found in 226 of 358 ewes by quantitative PCR. The frequency of ewes with detectable provirus did not differ significantly among the 171QQ, 171QR, and 171RR genotypes (p > 0.05). Also, OPPV provirus levels in infected ewes were not significantly different among codon 171 genotypes (p > 0.05). These results show that, in the flock examined, the presence of OPPV provirus and provirus levels are not related to the PRNP 171R allele. Therefore, a genetic approach to scrapie control is not expected to increase or decrease the number of OPPV infected sheep or the progression of disease. This study provides further support to the adoption of PRNP 171R selection as a scrapie control measure.

Lack of relationship between Visna/maedi infection and scrapie resistance genetic markers

“…Hence, the ongoing genetic selection for resistance to scrapie program is not expected to have a direct effect on the control and eradication of VMV infection based on antibody detection. As in the present study, Harrington et al (2009) did not find an association between scrapie and VM showing that VMV proviral levels in blood monocytes in infected sheep were not affected by the presence of arginine (R) at codon 171. The results of our work have an added value as they have a broader application because conclusions are based on more than 10,000 sheep from different flocks.…”

“…Among these studies, the resistance to infection by intestinal nematodes (Gruner et al, 2004) or by Salmonella spp. (Vitezica et al, 2007), the milk somatic cell count (de Vries et al, 2005;Álvarez et al, 2006), the specific immune system responses (Eaton et al, 2007) and the blood levels of VM provirus (Harrington et al, 2009) have been investigated.…”

Expanding Possibilities for Intervention against Small Ruminant Lentiviruses through Genetic Marker-Assisted Selective Breeding

“…Such measurements can reflect not only viral activity but also immunopathogenesis, in which immune responses from the host that can cause collateral damage in or near infected cells. However, since proviral concentration in peripheral blood is correlated with lesion severity [83] and provides a live animal test readily applicable to large numbers of animals, it is often used to measure control of viral replication [34,74,77,86]. …”

“…Accordingly, a large body of research addressed potential genotypic association with production traits including reproductive performance, wool characteristics, growth, body type, and dairy ability, among others [123,124,125,126,127,128,129,130,131,132,133]. Work was even done examining susceptibility to small ruminant lentiviruses [86]. Fortunately, most such studies have found no association, indicating a lack of apparent tradeoffs when making breeding decisions on the basis of PRNP genotypes.…”