- 學位論文
第二型豬環狀病毒疫苗注射實施前後之基因型別分析
Genotypic Analysis of Porcine Circovirus Type 2 Before and After Implementation of Vaccination in Taiwanese Swine Herds
摘要
第二型豬環狀病毒 (PCV2) 為一小型無封套單股環狀DNA病毒，屬於環狀病毒科之環狀病毒屬。PCV2為豬環狀病毒相關疾病之致病因子，於全球之養豬產業造成重大經濟損失。基於第二開放閱讀框 (open reading frame 2, ORF2) 之成對序列比對，PCV2可被分成三種基因型，PCV2a (包含五種子型，2A、2B、2C、2D及2E)，PCV2b (包含三種子型，1A、1B及1C) 及PCV2c。PCV2a及PCV2b此二基因型於全球廣泛流行，自2003報告主要基因型為PCV2b；第三種基因型PCV2c至今只曾於丹麥被報告過。近來分型受到較多的關注，因其中2010年於中國分離出之新興變異型mPCV2b似乎更具毒力。近三年有報告指出，mPCV2b已於美國及其他定期施打疫苗之國家傳播。故本研究之目的即在調查臺灣施打PCV2疫苗前後於豬群之PCV2之各型別盛行率。調查結果顯示於2012年至2015年間所分離出皆為PCV2b，其中26.8% (11/41) 為傳統型PCV2b，而73.2% (30/41) 為mPCV2b。本實驗室早期研究顯示，於2008年至2011年未施打PCV2疫苗期間，調查樣本中30% (6/20) 為傳統型PCV2b，而mPCV2b達70% (14/20)。總結以上結果，無論在有無施打PCV2疫苗之豬群中，主要流行型別以mPCV2b為主而非PCV2b。mPCV2b具有相對特殊之基因表現，並將取代PCV2a及PCV2b為主要田間流行病毒株。
並列摘要
Porcine circovirus type 2 (PCV2) is a small, non-enveloped, single-stranded, circular DNA virus that belongs to the genus Circovirus in the family Circoviridae. PCV2 is considered to be the primary causative agent of porcine circovirus-associated diseases in swine and causes significant economic losses in the global pork industry. Based on pairwise sequence comparisons of the open reading frame 2, PCV2 can be divided into three genotypes namely PCV2a with five clusters or subtypes (2A, 2B, 2C, 2D, and 2E), PCV2b with three clusters (1A, 1B, and 1C), and PCV2c. Among these, PCV2a and PCV2b have worldwide distribution with PCV2b being the predominant genotype reported since 2003. A third genotype, PCV2c has only been detected in Denmark to date. Recently, this classification received more attention, as it seemed to define mPCV2b to be more virulent. The mPCV2b, a new emerging subgroup of the PCV2b genotype, was first identified in China in 2010. In the last three years, several reports suggested that mPCV2b appeared to be widespread in the U.S farms, as well as in other countries where pigs were routinely vaccinated with the commercial PCV2 vaccine. Hence, the aim of this study was to investigate the prevalence of the PCV2 genotypes before and after implementation of vaccination in Taiwanese pig herds. The results revealed that all of isolates were PCV2b during 2012-2015. More interestingly, 26.8% (11/41) were classic PCV2b genotype and 73.2% (30/41) belonged to mPCV2b. In a recent study conducted by our group from 2008 to 2011, the non-vaccination period, the number of isolates with the classic PCV2b was 30% (6/20), while mPCV2b genotype made up 70% (14/20). Collectively, the majority of strains were more closely related to mPCV2b genotype than classic PCV2b both non-vaccinated and vaccinated pig populations. The mPCV2b strains have distinct genetic characteristics in comparison with classic PCV2a/b strains and were coming to replace classic PCV2a/b strains in the field.