Viral RNA load in semen from bluetongue serotype 8-infected rams: relationship with sperm quality

This study investigated if viral RNA was detectable in the semen of rams clinically infected with bluetongue virus serotype 8 (BTV-8) by RT-qPCR, and to what extent the amount detected may be predictive of sperm quality. Semen samples were collected on six occasions from 93 BTV-8 infected rams involved in two longitudinal (n=12 and 27, respectively) and one cross-sectional (n=54) field study. Semen quality was assessed in terms of mass motility, concentration of spermatozoa, percentage of living and dead spermatozoa as well as cytological features. An overall semen quality score (SQS) was established. Depending upon the studied population, BTV RNA was detected in 75-100% of semen samples at initial testing 25-57 days post-observation (DPO) of clinical signs, and was detectable up to 116 DPO in a proportion of rams undergoing repeated sampling. Semen quality variables were significantly altered following natural BTV-8 infection and correlated with the amount of BTV RNA present. The SQS did not return to normal when virus was no longer detectable, suggesting that clearance of BTV precedes full recovery of sperm quality. In conclusion, viral RNA may be transiently recovered from the semen of BTV-8 affected rams and may serve as an indicator in predicting ram breeding potential following natural infection.