豬離乳後多系統性消耗性症候群致病因子探討及豬環狀病毒二型分離株基因型之比較

Abstract

豬離乳後多系統消耗性症候群（Post-weaning multisystemic wasting syndrome; PMWS）於1991年首次在加拿大爆發，不過近來已成為各養豬產業國家重要的問題。豬環狀病毒二型（Porcine circovirus type II; PCV2）已被證明為造成PMWS的主要病原，但是一些共同因子，如其他病原的混合感染也被認為是造成PMWS的必要條件。本研究的目的為調查台灣PMWS的發生情況，並研究其他病原的混合感染是否為造成PMWS的條件。我們判定PMWS病例的標準是遵照之前的研究，共有三點：（1）出現相符的臨床症狀、（2）出現特徵性的組織病變、（3）這些變病區能以PCR偵測到PCV2。並且我們使用RT-PCR或PCR，針對Porcine circovirus typee I (PCV1), Pseudorabies virus (PRV), Porcine parvovirus (PPV), Classic swine fever virus (CSFV), Porcine reproductive and respiratory syndrome virus (PRRSV), Actinobacillus pleuropneumoniae (APP), Mycoplasma hyopneumoniae, Salmonella作檢測。本次調查62隻豬中，55隻PCV2陽性（88.71％）、29隻PPV陽性（46.77％）、25隻PRV陽性（40.32％）、6隻PCV1陽性（9.68％）、36隻Mycoplasma hyopneumoniae陽性（58.06％）、11隻APP陽性（17.74％）、42隻PRRSV陽性（67.74％）、10隻CSFV陽性（16.13％）、0隻Salmonella陽性。在各種檢體的PCV2檢出率方面，扁桃腺PCV2陽性率為80.65％（50/62）、肺門淋巴PCV2陽性率為82.26％（51/62）、肺臟PCV2的陽性率為75.81％（47/62）、肝臟PCV2陽性率為67.74（42/62）、脾臟PCV2陽性率為82.26％（51/62）、腸間淋巴結PCV2陽性率為80.65％（50/62）、腎臟的PCV2陽性率為79.03％（49/62）、鼠蹊淋巴結PCV2陽性率為85.48％（53/62）、血清PCV2陽性率為33.87％（21/62）。PMWS病例共有30隻，經由統計分析，發現感染CSFV (p=0.04)、PRRSV (p=0.0027)和PPV (p=0.0047)時，皆能增加造成PMWS的機率。另外將本研究的8個PCV2分離株作定序之後，與發表在GenBank上的PCV2台灣分離株作比較，相同度有93.1%到99.8%。若比較ORF2轉譯出之胺基酸，台灣各分離株相似度有88.5%到100%。而與全世界PCV2分離株作核酸序列比較，則相同度有93.4%到99.8%。

Post-weaning multisystemic wasting syndrome (PMWS), first described in Canada in 1991, has been now reported in most swine-producing countries and has become a significant problem for the pig industry. Porcine circovirus type 2 (PCV2) is the necessary cause of PMWS in swine; however, a variety of co-factors, including other infectious agents, are thought to be necessary in the full expression of disease. The aim of this study is to find out if other co-infection is necessary in the PMWS cases in Taiwan. The PMWS cases were diagnosed by three criteria described in previous study: (1) the presence of compatible clinical signs, (2) the presence of the characteristic microscopic lymphoid lesions, and (3) the detection of PCV2 within these tissues by PCR. Also, we detected Porcine circovirus typee I (PCV1), Pseudorabies virus (PRV), Porcine parvovirus (PPV), Classic swine fever virus (CSFV), Porcine reproductive and respiratory syndrome virus (PRRSV), Actinobacillus pleuropneumoniae (APP), Mycoplasma hyopneumoniae, Salmonella from different biological specimens of growth retarded pigs by RT-nPCR or PCR. In 62 pigs examined, 55 pigs were PCV2 positive (88.71%), 29 pigs were PPV positive (46.77%), 25 pigs were PRV positive (40.32%), 6 pigs were PCV1 positive (9.68%), 36 pigs were Mycoplasma hyopneumoniae positive (58.06%), 11 pigs were APP positive (17.74%), 42 pigs were PRRSV positive (67.74%), 10 pigs were CSFV positive (16.13%), 0 pigs were Salmonella positive and there were 30 PMWS cases. After statistic analysis, we found that co-infection with CSFV (p=0.04), PRRSV (p=0.0027), and PPV (p=0.0047) can increase the probability to induce PMWS. The nucleotide sequences of full-length genome of 8 Taiwan isolates were also analyzed by PCR and sequencing. After comparing nucleotide sequences of Taiwan strains published on GenBank, the PCV2 strains shared 93.1% to 99.8% identity. Comparing the amino acid sequences translated from ORF2 of PCV2 among the Taiwan strains, their amino acid sequences shared 88.5% to 100% similarity. The nucleotide sequences of PCV2 isolates shared 93.4% to 99.8% identity with other isolates world wide.