貓冠狀病毒感染：抗病毒藥物之臨床試驗及貓冠狀病毒3c基因之突變與貓傳染性腹膜炎關連性之探討

Feline coronavirus infection: antiviral agent in clinical trial and correlation of feline coronavirus 3c gene mutation with feline infectious peritonitis

唐大傑(Da-Jie Tang)

指導教授 ： 闕玲玲

共同指導教授 ： 蘇璧伶

國立臺灣大學/獸醫專業學院/獸醫學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.10681

摘要

貓傳染性腹膜炎 (Feline infectious peritonitis；FIP) 為一致命、免疫性媒介性疾病，其致病原為貓冠狀病毒 (Feline coronavirus；FCoV)。FCoV 廣泛分布於全世界貓群中，但只有 5~12%血清陽性的貓隻會發展成 FIP，大部分 FCoV 感染貓隻臨床上呈現輕微的腸炎或無症狀。截至目前為止，並無任何實驗室診斷的方法可以區分會發展成 FIP 之病毒，臨床上亦無有效的疫苗或治療。本論文針對貓冠狀病毒感染探討抗病毒藥物 Nelfinavir 在臨床上之應用：口服給予 9 隻感染 FCoV 貓隻抗病毒藥物 Nelfinavir 6.25~50 mg/kg， 投予時間最長達 24 週。追蹤其排毒情況發現，9 貓隻中投予藥物前 3 貓隻曾有病毒血症 (viremia)，口服藥物後2 貓隻血液中便偵測不到病毒，此外一貓隻自口服藥物兩週後，亦無偵測到病毒存在，然而其餘 8 隻動物其腸道依然在排毒。評估貓隻臨床症狀及血清生化學檢查之結果，並無發現藥物有明顯副作用。此外，由於貓冠狀病毒 3c 基因缺失曾經被懷疑過和病毒毒力相關，本研究藉由分析 19 株來自臨床健康貓及 11 株來自FIP 發病貓之 FCoV 3c 基因 ，探討貓冠狀病毒 3c 基因和 FIP 之間關聯性。結果發現健康貓身上之 FCoV 只有一株具有突變 3c 基因 (1/ 19； 5.3%)，且為 in frame 的序列缺失，推測其蛋白功能仍存，來自 FIP 發病貓之 FCoV 則大部分具有突變 3c 基因 ( 9 / 11；81.8%)：包括大小不一的序列缺失 (1∼595 nt)、點插入 (insertion)及點突變 (point mutation)，這些突變皆導致 3c 蛋白轉譯之提前終止。透過統計分析顯示，FCoV 3c 基因和 FIP 有極顯著的相關性 (P<0.01)。綜合上述實驗結果顯示，單獨投予 Nelfinavir 不具有抑制 FCoV 腸道感染之效應，而 FCoV 3c 基因突變與 FIP 有顯著相關，未來可以偵測此基因是否突變來設計 FCoV 感染發病與否之檢測，作為臨床上診斷 FIP 之依據。

關鍵字

貓冠狀病毒 ； 3c基因突變 ； 貓傳染性腹膜炎

並列摘要

Feline infectious peritonitis (FIP) is a fatal, immune-mediated disease in felids caused by feline coronavirus (FCoV). FCoV are widespread, however, only 5-12 % of seropositive cats develop FIP. Most infections are asymptomatic or result to mild enteritis. Up to present, there is no virological assay that can distinguish virulent from avriulent virus, moreover no effective vaccine or therapy is available for FIP. The objectives of this study were to perform a clinical trial for antiviral agents recently identified to be effective against FCoV infection in vitro, and to correlate the integrity of 3c gene of FCoV with FIP. Nine clinically healthy FCoV shedding cats from three multi-cat families were monitored. After taking Nelfinavir 6.25~50 mg/kg for up to 24 weeks, one infected cat stop shedding virus and two infected cats were no longer viremia, however most of the cats continue to shed FCoV from enteric tract. Through assessment of clinical signs and blood chemistry, no significant side effect was found. Deletions of FCoV 3c gene were reported to associate with viral virulence. In this study, 3c genes of FCoV were analyzed from 19 asymptomatic and 11 FIP cats. Of the 19 sequences analyzed, most are intact except one (5.3%) with a 3-nucleotide in frame deletion. Among the 3c genes from 11 FIP cats, only 2 were intact; the majority (81.8%) exhibited serious aberrations, including various deletions (1-595nt), insertion and point mutation. All these mutations result in premature termination of translation and truncation of the 3c polypeptide. Through statistical analysis, mutation of 3c gene demonstrates a significantly higher correlation with FIP (p<0.01).The preliminary results from clinical trial indicates that Nelfinavir when administrated alone can not eliminate viral shedding from chronic FCoV shedders. As the associating mutation of with FIP has been confirmed base on this finding, it is possible to develop an diagnostic assay for FIP in the near future.

並列關鍵字

Feline coronavirus ； Mutation of 3c gene ； Feline infectious peritonitis

參考文獻

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