The spread of Type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) in North America: A phylogeographic approach

Abstract

The emergence and spread of Type 2 Porcine Reproductive and Respiratory Syndrome virus (Type 2 PRRSV) in North America is heavily influenced by the multiple site production system used in the hog industry. However, it is unclear how anthropogenic factors such has this have shaped the current spatial distribution of PRRSV genotypes. We employed Bayesian phylogeographic analyses of 7040 ORF5 sequences to reveal the recent geographical spread of Type 2 PRRSV in North America. The directions and intensities in our inferred virus traffic network closely mirror the hog transportation. Most notably, we reveal multiple viral introductions from Canada into the United States causing a major shift in virus genetic composition in the Midwest USA that went unnoticed by the regular surveillance and field epidemiological studies. Overall, these findings provide important insights into the dynamics of Type 2 PRRSV evolution and spread that will facilitate programs for control and prevention.

Evolutionary diversification of type 2 porcine reproductive and respiratory syndrome virus

“…Comparisons of pairwise genetic distances between isolates in different regions of Canada (specifically Ontario and Quebec) and the USA revealing similar divergence is an outcome partly reflective of the intensive viral flow between the countries that has already previously been revealed through phylogeographical analyses (Shi et al, 2010b(Shi et al, , 2013b. This work by Shi and colleagues indicates that the continuous viral flow, especially in recent times, is gradually displacing previously endemic USA PRRSVs in the Midwest, Corn Belt, Lake States and Northern Plains with those that originated in Canada.…”

“…Thus, its role in PRRS may be important due to the appearance of recombinants associated with outbreaks (Shi et al, 2013a) or identified circulating in significant numbers over wide geographical areas originating from common ancestors (Shi et al, 2013b) when in the past only sporadic instances were detected (Li et al, 2009a, b;Yoshii et al, 2008).…”

“…Assuming that sequence divergence occurred by independent mutations at a constant rate, a number of lineages appeared to have become established before PRRS was recognized in the late 1980s. Later inclusion of additional datasets into the system indicated that all major groups of type 2 PRRSV have been identified (Brar et al, 2011;Kvisgaard et al, 2013;Shi et al, 2013b).…”

“…Seven of these lineages are still dominated by North American isolates, whilst the remaining two comprise primarily Asian isolates. Based on the topology of the phylogenetic tree and ancestral state reconstruction, it appears that lineages 1 and 2 originated in eastern Canada, whilst lineages 6 to 9 originated in the USA (Shi et al, 2013b). Global type 2 diversity is dominated mainly by isolates of four lineages (L1, L5, L8 and L9), which collectively constitute over 97 % of all ORF5 sequences (Fig.…”

“…In pairwise comparisons, China and Vietnam show reduced regional genetic variation due to the rapid spread of highly pathogenic PRRSV (HP-PRRSV) since 2006 and an accompanying explosion of PRRSV sequencing for outbreak isolates (Thuy et al, 2013;Tian et al, 2007;Zhou et al, 2011). In addition, the high growth rate of these viruses and facile transmissibility appears to have resulted in ecological displacement of previously resident strains, similar to the displacement of resident strains by sublineage 1.7-1.9 (MN184-like) viruses following their introduction into Minnesota, USA, in 2000 (Shi et al, 2013b;J. Torrison and M. P. Murtaugh, unpublished data).…”