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Porcine reproductive and respiratory syndrome virus (PRRSV) has long been an economically devastating swine viral disease. The recent emergence of a highly pathogenic type 2 PRRSV with high mobility and mortality in China, spreading in Vietnam, Laos, and Thailand has placed neighbouring countries at risk. This study applied a codon-based extension of the Bayesian relaxed clock model and the fixed effects maximum-likelihood method to investigate and compare the evolutionary dynamics of type 2 PRRSV for all of known structural envelope protein-coding genes. By comparing the highly pathogenic type 2 PRRSV clade against the typical type 2 PRRSV clade, this study demonstrated that the highly pathogenic clade evolved at high rates in all of the known structural genes but did not display rapid evolutionary dynamics compared with typical type 2 PRRSV. In contrast, the ORF3, ORF5 and ORF6 genes of the highly pathogenic clade evolved in a qualitatively different manner from the genes of the typical clade. At the population level, several codons of the sequence elements that were involved in viral neutralization, as well as codons that were associated with in vitro attenuation/over-attenuation, were predicted to be selected differentially between the typical clade and the highly pathogenic clade. The results of this study suggest that the multigenic factors of the envelope protein-coding genes contribute to diversifying the biological properties (virulence, antigenicity, etc.) of the highly pathogenic clade compared with the typical clade of type 2 PRRSV., (© 2013 Blackwell Verlag GmbH.)

Understanding viral transmission is an important factor for the effective prevention one of the most devastating swine diseases, porcine reproductive and respiratory syndrome. Focusing on molecular epidemiology of type 1 PRRSV, this study analysed a large ORF5 dataset collected worldwide from 1991 to 2012 using a coalescent-based Bayesian Markov chain Monte Carlo approach. The results suggested that the virus diversified into unique subpopulations in Russia & Belarus and Italy approximately 100 years ago. Previously unreported consecutive diffusions of the virus were identified, which showed that some countries, such as Spain and Germany, acted as distribution sources to some extent. This study also provided statistical evidence for the existence of an ORF5-based phylogeographical structure of type 1 PRRSV, in which the virus tended to cluster by geographical locations more tightly than expected by chance. In contrast to this tight geographical structure, the evolution of the ORF5 gene, based on mapping of non-synonymous/synonymous substitutions, was best described by a non-homogeneous process that could be implicated as a mechanism for viral immune evasion., (© 2013 Blackwell Verlag GmbH.)

Jeju island is the biggest island in Korea. The imports of pigs or their relatives from mainland Korea to this island has been banned since 1998. With this unique geographical and epidemiological context, epidemiology of porcine reproductive and respiratory syndrome virus (PRRSV) was investigated on the island. While all investigated farms showed 100% of seropositive rate for PRRSV, pigs on 37.2% (16/43) of the farms had viremia with type II PRRSV. The seropositive and viremia-positive rates for PRRSV in 30- to 60-day-old pigs were significantly higher in the western area ('swine farm complex' area) than the eastern area ('Scattered swine farm' area) of Jeju island. When 21 ORF5 sequences obtained from viremic sera were phylogenetically analysed, lineage 5 and Kor (newly termed in this study) of type II PRRSV were only found in Jeju island without changes from a previous report (2002-2003). Because other lineages of type II PRRSV (lineage 1 and 3) and type I PRRSV have recently emerged in mainland Korea, the banning of pigs' movement might be effective to protect the island from the introduction of these new PRRSV genotypes. Under this epidemiological condition (no introduction of new strains except for the modified-live vaccine (MLV) strain), the positive selection sites were analysed based on ORF5 of the virus. The amino acid 58 of GP5 (located on the hypervariable region) was predicted as a strong positive selection site. Although 51.2% (22/43) of the investigated farms had applied MLV, field strains of type II PRRSV were still circulating with strong positive selection. However, the restricted population of type II PRRSV (lineage 5 and Kor) without introduction of type I PRRSV or the other lineages of type II PRRSV indicate that the island has an effective quarantine system, which would allow PRRSV eradication., (© 2011 Blackwell Verlag GmbH.)