Virus Research 210 (2015) 34–41 Contents lists available at ScienceDirect Virus Research j ourna l ho me pa g e: www.elsevier.com/locate/virusres Emergence of a virulent porcine reproductive and respiratory syndrome virus in vaccinated herds in the United States Xiong Wang a , Douglas Marthaler b , Albert Rovira b , Stephanie Rossow b , Michael P. Murtaugh a,∗ a Department of Veterinary and Biomedical Sciences, University of Minnesota, 1971 Commonwealth Avenue, St. Paul, MN 55108, USA b Veterinary Diagnostic Laboratory, University of Minnesota, 1333 Gortner Avenue, St. Paul, MN 55108, USA a r t i c l e i n f o Article history: Received 27 May 2015 Received in revised form 2 July 2015 Accepted 3 July 2015 Available online 11 July 2015 Keywords: Type 2 PRRSV Virulent strain Full genome Phylogeny a b s t r a c t In early 2014, a Minnesota sow farm with a solid vaccination history suffered a severe porcine reproduc- tive and respiratory syndrome (PRRS) outbreak with unusually high morbidity and mortality in piglets and sows, as well as anorexia and secondary bacterial infections in nursery pigs. Due to the unusual clinical severity in a PRRS-immune herd, genetic characteristics of the virus were examined to deter- mine if a new PRRSV genotype had emerged. Phylogenetic analysis indicated that the virulent strain (PRRSV2/USA/Minnesota414/2014) was related to virulent strains circulating in the mid-western United States in recent years, and that the nonstructural protein 2 (nsp2) gene of MN414 contained an insertion- deletion pattern typical of existing type 2 virulent strains. We conclude that the MN414 isolate is a recently evolved member of the virulent lineage 1 family of type 2 PRRSV. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Porcine reproductive and respiratory syndrome (PRRS) is an eco- nomically critical swine disease that causes reproductive failure in sows, weak-born piglets, and respiratory disease with secondary infections in growing pigs. PRRS is caused by PRRSV, which belongs to the Arterivirus genus with a positive-sense single-stranded RNA of approximately 15 kb (Cavanagh, 1997; Hanada et al., 2005; Murtaugh et al., 2010). PRRSV have an extremely rapid evolution- ary rate and undergoes recombination, leading to increased genetic diversity, pathogenesis, and possible immune evasion. PRRSV is comprised of two genetically distinct groups, type 1 and type 2, initially isolated in Europe and North America, respectively. Both groups are genetically divergent and have ≥25% nucleotide sequence variation in open reading frame (ORF) 5 or ORF7 (Stadejek et al., 2006, 2008; Batista et al., 2004; Shi et al., 2010; Brar et al., 2012; Key et al., 2001). Since the discovery of PRRS in the late 1980s, virulent type 2 strains have emerged period- ically, including “atypical PRRS” in 1996, highly pathogenic Chinese PRRSV in 2006, and multiple offshoots of lineage 1 viruses starting in 2000 (Shi et al., 2010; Mengeling et al., 1998; Han et al., 2006; Yeske and Murtaugh, 2008; Tian et al., 2007). The novel virulence ∗ Corresponding author. E-mail address: murta001@umn.edu (M.P. Murtaugh). characteristics of PRRSV may be due to random chance, selective evolution, the identification of new isolates, or a combination of the previously listed characteristics. Here, we report a genetic and phylogenetic analysis of a highly virulent PRRSV isolate, designated PRRS/USA/Minnesota414/2014 (MN414/2014), that appeared in June 2014, in a Minnesota pig farm that suffered a severe PRRS outbreak with high morbidity and mortality in sows and piglets, even though the herd was vacci- nated quarterly. Initial ORF5 sequence analysis revealed only 93% nucleotide identity to existing reference sequences in the Uni- versity of Minnesota Veterinary Diagnostic Laboratory (UMVDL) database and no closely similar virus in GenBank. The combination of severe clinical signs and low nucleotide percent similarity sug- gested the possible emergence of a new, virulent PRRSV strain. The whole genome was sequenced, and phylogenetic analysis indicated that the virus emerged from within lineage 1 of type 2 PRRSV. 2. Materials and methods 2.1. Clinical case For 2 years prior to June 2014, a 5000-sow air-filtered herd in Minnesota was mass vaccinated four times per year with PRRS ATP (Boehringer Ingelheim, St. Joseph, MO). The herd was moved to an unfiltered farm following a fire and, 2 weeks later in June, 2014, a wild-type PRRSV, designated MN414/2014, was identified. Within http://dx.doi.org/10.1016/j.virusres.2015.07.004 0168-1702/© 2015 Elsevier B.V. All rights reserved.