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


METHODS
The 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.


CONCLUSIONS
To 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.
Korea Zoonosis Research Institute, Chonbuk National University, Iksan, South Korea. lks1314@jbnu.ac.kr.
Kwang-Soo
KS
Lyoo
Department of Pharmacy, College of Pharmacy, Korea University, Sejong, South Korea. paransearo@naver.com.
Minjoo
M
Yeom
Dodam Veterinary Clinic, Seoul, South Korea. vetcjy@hanmail.net.
Jong-Young
JY
Choi
College of Veterinary Medicine, Jeonnam National University, Gwangju, South Korea. jonpark94@naver.com.
Jong-Hwan
JH
Park
Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea. syoon@kribb.re.kr.
Sun-Woo
SW
Yoon
Department of Pharmacy, College of Pharmacy, Korea University, Sejong, South Korea. sds1@korea.ac.kr.
Daesub
D
Song
D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D005838:Genotype; D008168:Lung / Q000473:pathology; D010802:Phylogeny; D019318:Porcine Reproductive and Respiratory Syndrome / Q000453:epidemiology / Q000473:pathology*; D019316:Porcine respiratory and reproductive syndrome virus / Q000235:genetics / Q000472:pathogenicity; D056910:Republic of Korea / Q000453:epidemiology; D013552:Swine; D014774:Virulence