Genetic resistance - an alternative for controlling PRRS?

Gerald Reiner

PRRS is one of the most challenging diseases for world-wide pig production. Attempts for a sustainable control of this scourge by vaccination have not yet fully satisfied. With an increasing knowledge and methodology in disease resistance, a new world-wide endeavour has been started to support the combat of animal diseases, based on the existence of valuable gene variants with regard to any host-pathogen interaction. Several groups have produced a wealth of evidence for natural variability in resistance/susceptibility to PRRS in our commercial breeding lines. However, up to now, exploiting existing variation has failed because of the difficulty to detect the carriers of favourable and unfavourable alleles, especially with regard to such complex polygenic traits like resistance to PRRS. New hope comes from new genomic tools like next generation sequencing which have become extremely fast and low priced. Thus, research is booming world-wide and the jigsaw puzzle is filling up - slowly but steadily. On the other hand, knowledge from virological and biomedical basic research has opened the way for an "intervening way", i.e. the modification of identified key genes that occupy key positions in PRRS pathogenesis, like CD163. CD163 was identified as the striking receptor in PRRSV entry and its knockout from the genome by gene editing has led to the production of pigs that were completely resistant to PRRSV - a milestone in modern pig breeding. However, at this early step, concerns remain about the acceptance of societies for gene edited products and regulation still awaits upgrading to the new technology. Further questions arise with regard to upcoming patents from an ethical and legal point of view. Eventually, the importance of CD163 for homeostasis, defence and immunity demands for more insight before its complete or partial silencing can be answered. Whatever path will be followed, even a partial abolishment of PRRSV replication will lead to a significant improvement of the disastrous herd situation, with a significant impact on welfare, performance, antimicrobial consumption and consumer protection. Genetics will be part of a future solution.