Technical Abstract: Selective breeding of sheep for arginine (R) at prion gene (PRNP) codon 171 confers resistance to Scrapie. The 171R allele naturally occurs at low frequency, possibly because it imparts a deleterious trait such as impaired disease resistance. Ovine Progressive Pneumonia/Maedi-Visna virus (OPPV) is the primary economically important infection of sheep. If 171R selection affects OPPV it could significantly impact the sheep industry. A hypothesis that the PRNP 171R allele is associated with positive OPPV infection and higher OPPV proviral load was tested in an Idaho sheep flock using a logistical regression model that included breed, age, and interaction between breed and age as variables. OPPV provirus was found in 226 of 358 sheep by quantitative PCR. The frequency of OPPV positive animals did not differ significantly between the 171QQ, 171QR, and 171RR genotypes (p>0.05). OPPV proviral load levels of infected sheep were not significantly different among codon 171 genotypes (p>0.05). A minor allele at codon 143 was also examined. OPPV status and OPPV proviral load were statistically equivalent between 143 HH and 143 HR genotypes (p>0.05). This experiment shows that, in the flock examined, OPPV infection status and proviral load are independent of the PRNP 171R and 143R alleles. These results indicate that a genetic approach to Scrapie control is not expected to impact host resistance to OPPV and supports the adoption of PRNP 171R selection as a Scrapie control measure.