Porcine reproductive and respiratory syndrome (PRRS) virus appeared 20 years ago as the cause of a new disease in swine. Today PRRS is the most significant swine disease worldwide in spite of intensive immunological interventions. The virus showed remarkable genetic variation with two geographically distinct genotypes at the time of its discovery, indicating the possibility of prolonged evolutionary divergence prior to its appearance as a swine pathogen. Since then, both type 1 and type 2 have spread geographically, radiated genetically, and acquired new phenotypic characteristics, especially increased virulence. Here, we explore various hypotheses that might account for rapid expansion and diversification of PRRSV, including mechanisms specific to PRRSV and other arteriviruses, cellular modification processes, and immunological selection. Phylogenetic analysis of PRRSV has provided a broadly applicable means to relate diverse isolates, but it does not explain biological variation in virulence or immunological cross-protection. We present other methods of classification and review their limitations. Major questions about PRRSV remain unanswered despite intensive investigation, suggesting that the interaction of PRRSV with pigs involves novel biological processes that may be relevant to other RNA virus and host interactions.
Bibliographical noteFunding Information:
The work and ideas presented here were generated in part with support by the PRRS Coordinated Agricultural Project funded through USDA Cooperative State Research, Education and Extension Service , grant numbers 2004-35605-14197 and 2008-55620-19132 , the Strategic Research Theme of Infection and Immunology from The University of Hong Kong , the Polish Ministry of Science and Higher Education no. NN308265136, EU FP7 grant no. 245141, and EU COST Action FA902.
Copyright 2019 Elsevier B.V., All rights reserved.
- Hog production
- North America
- RNA virus