| Summary: | 碩士 === 國立屏東科技大學 === 獸醫學系所 === 103 === 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.
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