Genetic diversity of imported PRRSV-2 strains, 2005-2020, Hungary

Abstract

Porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) remains sporadic in Europe. In this study, we investigated the molecular epidemiology of PRRSV-2 infections encompassing 15 years in Hungary. Partial (423 bp long) ORF5 sequences (n = 44) from 20 Hungarian pig herds were analyzed. The study strains fell into two genetic lineages, L1 and L5, being L5 strains more prevalent (88.6 vs. 11.4%). Pairwise sequence identities within Hungarian representative PRRSV-2 strains ranged between 84.7 to 100% (nucleotide, nt) and 85 to 100% (amino acid, aa). When compared with reference strains, identity values fell between 87 and 100% (L1, nt 87-91%, aa 87-93%, reference strain IAF-exp91; L5, nt 87-100%, aa 88-100%, reference strain Ingelvac MLV). Epidemiologic examination implied that the majority of L5 strains were imported repeatedly from other European countries where Ingelvac MLV was approved for routine use. The emergence of L1 strains was thought to be associated with a single introduction and subsequent dissemination between pig farms of a large integrator. Results presented here contribute to a better understanding of the epizootiology of PRRSV-2 infections and shed light on the genetic diversity of viral strains in non-endemic countries.

Keywords: Betaarterivirus suid 2; ORF5; molecular epidemiology; phylogenetic analysis; vaccine virus.

Figure 1

(A) Phylogenetic analysis based on global ORF5 sequence dataset including European sequences (n = 977) of PRRSV-2. Maximum likelihood method with TVM+F+R8 model and 1,000 ultrafast bootstrap were utilized. (B) Lineage 5 and a (C) part of lineage 1 sub-trees were expanded for further presentation. The different geographic origin of the sequences were marked with distinct colors. Red circles () denote the partial ORF5 sequences determined in this study; each dot represents an individual sequence. Prototype strain VR2332 () and the vaccine strain Ingelvac MLV () are indicated separately.

Figure 2

Spatial distribution of all pig farms that were infected with PRRSV-2 from 2005 to 2020. The location of the farms were designated by different colored markers according to the detected lineage of PRRSV-2. Origin of imported fattening stocks were also displayed (for further details the reader is referred to Table 1).

Figure 3

Multiple alignment of the partial GP5 amino acid sequences of all Hungarian isolates of PRRSV-2 from 2005 to 2020 together with reference strain IAF-exp91 and VR2332 (The reader is referred to Supplementary Figure 1 for the colored signs). Epitope sites and highly variables regions are represented by blank boxes and gray boxes, respectively. The site of attenuation of VR2332 is indicated in the red box.