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Emergence of novel RNA viruses in swine herd in Korea : 국내 돼지 농가에서의 새로운 RNA 바이러스들의 출현

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Authors

이지훈

Advisor
박봉균
Major
수의과대학 수의학과
Issue Date
2016-02
Publisher
서울대학교 대학원
Keywords
돼지 인플루엔자 바이러스돼지 유행성 설사병 바이러스돼지 델타코로나바이러스RNA virus
Description
학위논문 (박사)-- 서울대학교 대학원 : 수의과대학 수의학과 수의미생물학전공, 2016. 2. 박봉균.
Abstract
In swine industry, contagious diseases are constantly around and suddenly outbreak in particular places in swine producing countries with enormous economic losses although various prevention methods have been applied for control. Furthermore, some of them are more threat for public health if they have the zoonotic potentials by genetic reassortant or mutation. Overall objectives of present researches were to elucidate characteristics of newly emerged RNA viruses, such as swine influenza (Orthyomyxovirus), porcine epidemic diarrhea and delta-coronavirus (Coronaviruses) in South Korea.
Swine influenza virus (SIV) causes an acute respiratory disease in pigs and sporadic human outbreak. The H1N1, H1N2, and H3N2 SIV subtypes are endemic in major swine producing counties. In Korea, North American triple reassortant SIVs which possess a gene combination of human, classical swine, and avian segments have been circulating for decades although triple reassortant H1N2 strains (with a classical swine-like hemagglutinin) are exclusively predominant. Since the first report of the emergence pandemic (H1N1) 2009- A(H1N1)pdM09 virus of in North America in June 2009, similar viruses bearing a unique reassortment of segments derived from the triple reassortant swine North American lineage and the avian-like swine Eurasian lineage were also reported in swine and human population worldwide. Most recently, novel reassortant A(H1N2) SIVs bearing Eurasian avian-like swine H1-like hemagglutinin and Korean swine H1N2-like neuraminidase in the internal gene backbone of the H3N2pM-like virus, represented by A/swine/Korea/CY0423/2013 (CY0423-12/2013), were also identified in Korean domestic pigs. In order to investigate overall characteristics of novel CY0423-12/2013-like SIVs, in first chapter, the genetic analyses with all eight gene segments were characterized and evaluated their pathogenic potentials in vitro and in vivo studies. Genetic characterization results revealed that the HA gene of CY0423-12/2013 showed high genetic homology with EA avian-like swine H1 viruses while N2 NA gene is more closely related with current existing Korean H1N2 SIVs. The other six internal genes were highly similar with those of swine H3N2pM-like viruses identified in Korea and North America. Compare to Korean classical H1N2 SIV (CY03-11/2012), the novel CY0423-12/2013 showed more efficient viral replication in human bronchial epithelial cells and induce higher level of viral titer in both infected mouse and ferret model. In addition, the CY0423-12/2013 can transmit via respiratory route through air contact to naïve ferret from infected. These findings indicated divergence of recent SIVs in Korea also provide zoonotic possibility of reassortant H1N2 SIV since it contains reassorted genes from other species which can affect and transmit to human.
Porcine epidemic diarrhea virus (PEDV), a member of the family Coronaviridae, is an enveloped, single-stranded RNA virus. After PEDV was first identified in Europe in 1978 and North America in 2013, outbreaks of PEDV infections have been reported in many other countries including South Korea (1992). Although several PEDV vaccines were developed and applied in fields, PEDV have been continued outbreaks and caused serious economic damages in Korean pig farms. Therefore, in second chapter, isolation of PEDV from Korean swine farms was conducted and demonstrated their genetic characteristics. During the 2014 to 2015, total 30 PEDV positive fecal samples were collected from domestic farms in Korea, and two PEDV strains (J3142 and BM3) were isolated. Genetic analysis of complete Spike gene of two isolates showed that both strains had high similarity with strains of geno subgroup G2a, while current PEDV vaccine strains are belonged to subgroup G1. In addition, the BM3 showed high genetic homology with those of North America, but the J3142 showed more genetic relation with China strains in S2 region. Nucleotide comparison of both Spike complete genes and N-terminal domains in 2 isolates showed low identity only 89.2~89.5 percent with those of vaccine strains (DR13 and CV777). Molecular analysis of two isolates, a specific substitution at neutralizing SS6 epitope was found in both SM3 and J3142 strains compared with vaccine strains. Furthermore, potential recombinant region was found in J3142 strain with KNU1303_Korean strain (subgroup G2a) or KF724935_Thailand strain (subgroup G2b) by using Recombination Detection Program with reference strains. These results suggested that at least two different subgroups of PEDV are co-circulated and they are undergoing continuous genetic evolution in Korean swine herds.
In February 2014, a novel deltacoronavirus in swine, called procine deltacoronavirus (PDCoV) was first identified in the US, Ohio and Indiana, followed by rapid transmit to other states in the US and Canada. Although the origin and virulence of this novel porcine coronavirus are still unclear, genetic analyses revealed that the US PDCoV isolates possess unique characteristics and showed a close relationship with PDCoV isolates of Hong Kong and South Korea. Therefore, in third chapter, isolation of PDCoV from Korean swine farms was conducted and demonstrated their genetic characteristics. To this end, a total 681 samples from 59 commercial swine farms were tested to investigate the presence of PDCoV, and 2 strains (SL2 and SL5) were discovered in a farm in Gyeongbuk province in Korea. The pigs of the farm showed severe diarrhea similar symptoms with normal PEDV activity but different disease pattern compared with previous PEDV only cases. Based on phylogenetic analysis of complete Spike and Nucleocapsid genes, SL2 and SL5 were closely related to the strains of North America PDCoV rather than those of China PDCoV. In addition the SL2 and SL5 showed different genetic characteristic with previously reported KNU14.04_Korean strain.
Overall, the present studies provide knowledge to various characteristics of newly identified swine RNA viruses of SIV, PEDV and PDCoV in Korea. Upon the situation of fast changing of contagious pathogens, especially in RNA viruses, rapid and accurate actions of various research trials should be worthy to efficient control and prevention against newly emerging infectious diseases. Therefore, persistent monitoring and systematic surveillance should be maintained for containment purposes and to reduce opportunities for further genetic evolution of the virus.
Language
English
URI
https://hdl.handle.net/10371/120236
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