台灣地區2018-2020年豬第二型環狀病毒基因型別及基因多樣性之調查

Genetic diversity and genetic analysis of porcine circovirus type 2 from 2018 to 2020 in Taiwan

連柏蓉(Lian Bo-Rong)

指導教授 ： 邱明堂 ； 林昭男

國立屏東科技大學/獸醫學院/獸醫學系所/碩士(2020年)

https://doi.org/10.6346/NPUST202100158

摘要

豬環狀病毒相關疾病（porcine circovirus-associated diseases, PCVAD）由豬第二型環狀病毒（porcine circovirus 2, PCV2）所引起。雖商業化PCV2疫苗於台灣已上市長達十餘年，但本病仍偶見於各年齡豬隻，顯示此病對養豬業仍深具威脅。PCV2根據第二開放讀碼區 （Open reading frame 2, ORF2）之核苷酸序列的差異，可分成 PCV2a-2i九個基因型。由於PCV2高核苷酸變異率之特性，使其持續變異甚至出現新的基因型別。此病毒於分別於2003及2012年前後，發生兩次全球性基因型轉變。為調查台灣目前流行PCV2基因型別與基因多樣性，本研究收集2018至2020年間送檢至國立屏東科技大學動物疾病診斷中心診斷為PCV2感染症豬隻共135個血清或組織檢體，將PCV2 ORF2片段增幅與純化後定序，交叉比對分析國內外發表序列。結果顯示目前台灣仍以PCV2d為主要流行基因型別，自2016年至2020年間，PCV2d佔所有PCV2感染案例達95%以上。然而PCV2g與PCV2b分別自2006年與2015年後皆未再被檢測出，另本研究於2019年首次在台灣檢測出PCV2e。此外，針對PCV2 ORF2核苷酸間相似度分析，可見PCV2a之間相似度為95.0-96.9%；PCV2d之間相似度為96.7-100.0%；PCV2a與PCV2d之間相似度為88.2%-90.0%；PCV2a與PCV2e之間相似度為81.1%-81.2%；PCV2d與PCV2e之間相似度為83.3%-84.4%。比對PCV2 ORF2胺基酸序列相似度上，可見PCV2a之間相似度為94.9%-96.2%；PCV2d之間相似度為94.5-99.6%；PCV2a與PCV2d之間相似度為86.3%-90.6%。PCV2a與PCV2e之間的相似度為80.8%-81.2%；PCV2d與PCV2e之間的相似度為81.2%-83.0%，顯示PCV2至今仍持續變異。而根據PCV2 ORF2胺基酸模式圖顯示PCV2d出現變異胺基酸包括A59K，K88P與T134N，而其變異是否會降低中和抗體之中和能力進而影響PCV2疫苗之成效則須進一步研究證實。

關鍵字

豬第二型環狀病毒 ； 基因多樣性 ； 基因型轉變

並列摘要

Porcine circovirus type 2 (PCV2) is the causative antigen of porcine circovirus-associated disease (PCVAD). Although PCV2 vaccine has been introduced in Taiwan over for a decade, this disease still can be detected in pig herds. Based on differences in ORF2 nucleotide sequences, the genotypes of PCV2 have been classified as 9 genotypes (PCV2a to PCV2i). Because of high mutation rate, PCV2 has been continuously emerging novel strains. Twice global genotype shifts occurred from PCV2a to PCV2b around 2003 and from PCV2b to PCV2d around 2012. The purpose of this study is to investigate the dominant genotype and genotypic diversity of PCV2 in Taiwan. Serum and/or tissue samples collected from PCV2-infected pigs in Animal Disease Diagnosis Center of National Pingtung University of Science and Technology during the period from 2018 to 2020. The 135 PCV2 ORF2 sequences were performed nucleotide sequences analysis and compared with other PCV2 ORF2 sequences from Taiwan and other countries. The results show that PCV2d is still dominant genotype in Taiwan from 2018 to 2020 and above 95% PCV2 infection pigs were caused by PCV2d from 2016 to 2020, and others genotypes sporadic cases in Taiwan. Furthermore, PCV2e was reported for the first time in Taiwan in 2019 but PCV2g and PCV2b have not been detected since 2006 and 2015 respectively. According to the analysis of PCV2 ORF2 nucleotides, the identity of PCV2a and PCV2d, the identity of PCV2a between PCV2d, PCV2a between PCV2e and PCV2d between PCV2e are 95.0-96.9%, 96.7-100.0%, 88.2%-90.0%, 81.1%-81.2% and 83.3%-84.4%. According to the analysis of the 168 Taiwanese PCV2 ORF2 nucleotides, the identity of PCV2a and PCV2d, the identity of PCV2a between PCV2d, PCV2a between PCV2e and PCV2d between PCV2e are 94.9%-96.2%, 94.5-99.6%, 86.3%-90.6%, 80.8%-81.2% and 81.2%-83.0%. This information showed that PCV2 mutated continuously from 2018 to 2020. According to schematic amino acid of putative PCV2 capsid protein, PCV2d capsid protein mutations A59K, K88P and T134N. However, whether amino acids substitution may affect neutralization efficiency and the effect on PCV2 vaccine should be further investigated.

並列關鍵字

Porcine circovirus type 2 (PCV2) ； genetic diversity ； genotype shift

參考文獻

潘虹演 (Phan, Hong-Dien) (2015) 第二型豬環狀病毒疫苗注射實施前後之基因型別分析。國立屏東科技大學獸醫學研究所碩士論文，未出版。2015年7月28日，取自「國立屏東科技大學博碩士論文系統」：http://etd.lib.npust.edu.tw/

Allan, G. (2002) PCV2: ticking time bomb. Pig Prog 18: 14-15.

Allan, G., S. Kennedy, F. McNeilly, J. Foster, J. Ellis, S. Krakowka, B. Meehan, and B. Adair (1999) Experimental reproduction of severe wasting disease by co-infection of pigs with porcine circovirus and porcine parvovirus. J Comp Pathol 121: 1-11.

Allan, G., F. McNeilly, J. Cassidy, G. Reilly, B. Adair, W. Ellis, and M. McNulty (1995) Pathogenesis of porcine circovirus; experimental infections of colostrum deprived piglets and examination of pig foetal material. Vet Microbiol 44: 49-64.

Baft, B. (1996) Interstitial pneumonia and lymphadenopathy associated with ciroviral infection in a six-week-old pig. Proc Am Assoc Vet Lab Diag 39: 32.