| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 88 === Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped virus with positive sense of RNA genome. This RNA genome is 15 Kb in size and encodes 8 open reading frames (ORFs). Among those, ORF 5 encoding protein, a glycosylated membrane protein, is responsible for the induction of neutralization antibody. Based on the ORF 2-ORF 7 sequence comparison, two PRRSV groups, namely the American and European, were identified. Previous studies showed that the Taiwan PRRSV isolates MD001 belongs to the American group. However, the identity of ORF 5 amino acids sequence between MD001 and American VR-2332 is 84%. The objective of the present study was to evaluate the ORF 5 genetic variation of PRRSV isolates in Taiwan, in comparison with MD001 and American VR-2332. Ninety-nine PRRSV isolates from 19 pig farms were analyzed based on restriction fragment length polymorphism (RFLP) of ORF5. After amplification of ORF5 by reverse transcription polymerase chain reaction (RT-PCR), RFLP was done by digestion of three restriction enzymes, MluI, HincII, and SacII on those amplified products. Our results showed that all 99 PRRSV isolates do not have the restriction enzyme site for Mlu I. Thirteen different combined restriction patterns have been found among these isolates. Also, two different combined restriction patterns co-existed in 5 pig farms when the isolates were collected at the same time period. Moreover, two farms had shown the pattern changes within three years. No significant relationship has been observed between the geographic distribution and the combination of restriction patterns. Eight different combinations of restriction patterns prevailed among Taiwan pig farms; while there was 5 unique patterns existed in one single farm each. The results showed that broad ORF 5 genetic diversity exists among PRRS virus strains in Taiwan. However, all these strains could be differentiated from the VR-2332 reference strain based on different restriction patterns.
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