Unusual severe cases of type 1 porcine reproductive and respiratory syndrome virus (PRRSV) infection in conventionally reared pigs in South Korea.

Jong-Hwan Park,Sun-Woo Yoon,Daesub Song,Minjoo Yeom,Jong-Young Choi,Kwang-Soo Lyoo

doi:10.1186/s12917-015-0584-5

Abstract

BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) causes a loss of approximately US$ 70 million every year to the South Korean pork industry. There are two distinct genotypes: European (type 1) and North American (type 2). In South Korea, type 1 and type 2 PRRSV are widely distributed and have evolved continuously since the infection was first described. Here, we present two field cases of type 1 PRRSV infection with unusually severe pathogenicity.Case presentationThe first case farm was a two-site production system comprising farrow-to-grower and grower-to-finish units and was historically free from PRRSV infections. The PRRSV vaccine had not been used in both units. In October 2014, pigs in the grower-to-finish unit experienced severe respiratory distress with the mortality rate reaching to 22 %. Despite antibiotic treatment, clinical signs were still noticed in most pigs. The second case farm was also a two-site production system, but had two separate farrow-to-grower units (unit A and unit B). Historically, type 1 PRRSV was continuously present in unit A, but unit B was free from PRRSV. Thus, all grower pigs of unit B were vaccinated before being moved to the grower-to-finish unit. In November 2014, severe respiratory distress was seen in pigs of the grower-to-finish unit. Significant respiratory distress was observed in only the grower herd moved from unit B, and the mortality of those pigs was ~50 %. However, no disease was shown in the grower pigs from unit A.ConclusionsTo our knowledge, the present study is the first observation of the cases of infection by highly pathogenic type 1 PRRSV in South Korea. The Korean type 1 PRRSV strains have undergone unique evolutionary dynamics for the last decade in this country. Although there are known to be three clusters of Korean type 1 PRRSV, their pathogenicity could not be categorized owing to their high level of genetic diversity. Therefore, further studies are needed to demonstrate the novel classification of Korean type 1 PRRSV strains according to their virulence factors.

Highlights

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a loss of approximately US$ 70 million every year to the South Korean pork industry
To our knowledge, the present study is the first observation of the cases of infection by highly pathogenic type 1 PRRSV in South Korea
There are known to be three clusters of Korean type 1 PRRSV, their pathogenicity could not be categorized owing to their high level of genetic diversity

Summary

Conclusions

The present findings are the first observation of cases of infection by a highly pathogenic type 1 PRRSV in conventionally reared pigs in South Korea. Korean type 1 PRRSV strains have undergone unique evolutionary dynamics for the last decade in this country, the observation of severe respiratory disease by a single infection with type 1 PRRSV has not been verified because the disease problems from type 2 strains are more common in South Korea. It was essential that the case farms had to have been monitored by a veterinarian for a long period for those cases to be recognized. Further studies are needed to demonstrate the novel classification of Korean type 1 PRRSV strains according to their virulence factors of the virus. Authors’ contributions KSL and MY performed laboratory examinations and wrote the manuscript. JYC monitored the two swine farms and collected samples.

Background

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Discussion