被動免疫與抗病毒藥物於犬瘟熱治療之評估

Abstract

犬瘟熱 (Canine distemper, CD) 為一高傳染性和高致死率的疾病，常造成全身系統性的感染，並伴隨著免疫抑制，嚴重者則會出現神經症狀。雖然透過疫苗注射使疫情受到控制，但世界各地仍間歇性有病例發生且近年有增加趨勢，其中不乏已接受過完整疫苗接種計畫的犬隻；整理台大分子生物學研究室針對犬瘟熱病毒 (canine distemper virus, CDV) 核酸檢測發現，過去10年來有超過328個CD病例，可知本病在台灣仍十分普遍。由於在臨床上尚未有有效的治療方針，為提高罹患本病動物之治癒機會，本研究利用CDV之抗血清以被動免疫嘗試治療發病犬隻，評估其療效，並尋找合適的抗病毒藥物。分析13個接受不同劑量犬源抗血清治療的臨床病例發現，在治療始點尚未出現神經症狀的4隻患犬，百分之百耐過，恢復健康；而就診時已出現神經症狀的9隻患犬中，僅有4隻耐過 (佔44%)，另5隻死亡 (佔56%)；整體治療結果，總計有8隻 (佔61.5％) 恢復，5隻 (佔38.5%) 死亡，顯示給予血清治療有一半以上的病犬耐過，且整個療程間接受到較高中和力價抗血清之犬隻呈現出較好的療效。此外為尋找有效的抗病毒藥物，針對新分離出的CDV本土株做藥物試驗，此病毒株於一隻四歲齡、有定期施打疫苗的犬隻中分離出，經由免疫螢光染色及基因定序確認為CDV，且測試了15種商品化藥物進行抗病毒效應之體外評估，於B95a細胞中以MTT試驗評估藥物之毒性，結果顯示Ribavirin在濃度30μM下，可達50%有效抑制CDV複製的效果，而Interferon-α (IFN-α) 在濃度9000 IU/mL下，也能抑制CDV複製。以上研究指出，透過具中和力價之CDV抗血清治療能幫助約半數病犬耐過疾病，未來若能合併抗病毒藥物以抑制病毒之複製，並搭配合適的免疫調節藥物，或能有機會協助發病動物及早恢復或免於死亡。

Canine distemper virus (CDV) is a highly contagious pathogen of carnivores causing high mortality disease. CDV infection can result in a systemic infection with severe immunosuppression, frequently followed by central nervous system involvement. Despite extensive vaccination, CD remains to be a major disease of dogs in both unvaccinated and vaccinated dogs. The disease is common in Taiwan as more than 328 cases were confirmed in the past decade (2000-2010) in NTU animal hospital. To date, except for supportive treatment, no effective treatment for CD is avaible. To help dogs recover from CD, the therapeutic effect of hyperimmune serum in clinical CD cases were evaluated and 15 compounds were screened for their anti-CDV activity in vitro. Among the 13 clinical CD cases receiving hyperimmune serum therapy, all 4 dogs (30.8%) presented without neurological symptoms recovered. Among the 9 dogs (69.2%) presented with neurological symptoms, 4 dogs (44%) recovered and 5 dogs (55.6%) died. To search for antiviral agents against CDV infection in vitro, a virus causing syncytial cytopathic effect was isolated from a 4-year-old dog. The virus was purified and confirmed by immunofluorescence assay and sequencing to be a CDV. Using this new isolate NTU311, 15 commercial antiviral agents were tested. The result showed that 30μM of Ribavirin exhibited 50% inhibitory effect against CDV in vitro and that 9000 IU/ml of IFN-αalso exhibited inhibitory effect. These results suggest that combined use of antiserum, antiviral drugs and immunomodulator has therapeutic potential in treatment of dogs with CD.