貓冠狀病毒流行病學之調查與貓傳染性腹膜炎相關宿主因子之探討

Epidemiological surveillance of feline coronavirus infection and feline infectious peritonitis associated host genetic polymorphisms

王映庭(Ying-Ting Wang)

指導教授 ： 闕玲玲

共同指導教授 ： 萬灼華(Cho-Hua Wan)

國立臺灣大學/獸醫專業學院/獸醫學研究所/博士(2015年)

https://doi.org/10.6342/NTU.2015.02704

摘要

貓冠狀病毒 (Feline coronavirus, FCoV) 之感染普遍存在於貓隻族群中。FCoV感 染貓隻多不會出現臨床症狀。然而在約< 5%的血清陽性貓隻會造成一高度致死性、免疫媒介性疾病,稱為貓傳染性腹膜炎 (Feline infectious peritonitis, FIP)。目前並未有有效的疫苗及治療。由於貓隻於FIP發病後 100%死亡,一旦確診後,臨床上通常建議安樂死。直至今日,仍有許多關於病毒及宿主基因差異性於發病所中扮演之角色的問題尚待釐清。本研究深入分析FCoV之傳播、流行病學及病毒演化,並找尋與FIP相關之宿主基因多型性以期運用於未來疾病之防控。
造成FIP之病毒 (FIPV) 目前被認為散發性地由感染貓隻體內突變而來且無法有效率的於貓隻間傳播。本研究室近期於台灣的私人動物收容所中觀察到FIP之爆發, 於所有 46 隻貓中,13 隻貓出現典型 FIP之臨床症狀。進一步分析發病動物體內病毒之S及 3c基因,證明其皆感染帶有相同之重組點之第二型 FCoV,本研究並確立 FIPV 於貓隻間水平傳播之可能性,因此 FIP 發病動物可能對同一環境中之貓隻造成潛在之危害。由於第二型 FCoV 被認為與 FIP 及疾病之爆發有相關性。為了鑑別兩血清型之病毒感染並進行流行病學之調查,透 過桿狀病毒表現FCoV型別特異性棘蛋白,用以進一步分析過往八年間兩血清型 FCoV 於台灣貓隻感染之情形。 結果發現第一型 FCoV 為主要感染之血清型 。此外,比較以此血清分型方法與基因分型結果,發現兩者具有高度之相關性。此結果亦支持目前對於FCoV演化及FIP傳播之認知。基於FIP致病機制屬於免疫媒介特性,宿主基因多型性被認為影響了FIP的發生與否。為找尋與FIP相關之宿主因子,分析貓隻腫瘤壞死因子 (Tumor necrosis factor alpha, TNF-α)、FCoV 受體C-type lectin DC-SIGN (CD209) 及五個於柏曼貓被報告與 FIP相關之單核苷酸多型性 (Single nucleotide polymorphism, SNP) 之基因多型性,以了解宿主背景因子與FCoV感染後發病與否之相關性。其中,於TNF-α促進子、fCD209之外顯子 (extracellular domain) 與三個位於fCD209之內插子之 SNPs發現與FIP發病相關。相對於此,5個先前被報告與柏曼貓發病相關之SNPs,於此研究則未檢測出與疾病相關。由於宿主對於疾病之感受性/抵抗性為多因子性,且許多不同之宿主基因可能同時影響了FIP的發生與否,於本研究中所找 尋之5個基因多型性差異點可以被運用於改善抗FIP動物之篩選,以期減少未來貓隻死亡。

關鍵字

貓冠狀病毒 ； 貓傳染性腹膜炎 ； 第二型貓冠狀病毒 ； 貓傳染性腹膜炎爆發 ； 桿狀病毒表現型別特異性棘蛋白 ； 血清盛行率 ； 宿主基因多型性 ； 腫瘤壞死因子 ； C 型凝集素

並列摘要

Feline coronavirus (FCoV) is an ubiquitous viral pathogen in the cat populations. The infection of FCoV is usually asymptomatic. However, less than 5% of the seropositive cats develop a highly lethal immune-mediated disease, feline infectious peritonitis (FIP). Until now, neither effective treatment nor protective vaccine is available. Euthanasia is suggested once the disease was diagnosed, as all FIP cats eventually died from this disease. To date, several questions remain unsolved regarding roles of the virus and the host genetic factors contributing to the development of FIP. The virus that causes FIP (FIPV) is believed to occur sporadically and spread infrequently from cat to cat. However, an FIP outbreak from a private animal shelter that causes 13 out of 46 cats died from FIP was confirmed in our lab recently. Sequence analysis of the S and 3c gene showed that the FIPVs of the outbreak were from the same origin and the results indicate that horizontal transmission of FIPV is possible and that FIP cats can pose a potential risk to other cats living in the same environment. Serotype II FCoV was suggested to be significantly correlated with FIP and an outbreak caused by this type of FCoV has been confirmed. A Baculovirus-expressed type-specific spike proteins based assay was used fro the seroprevalence study of two types of FCoV in the past eight years in Taiwan was firstly carried out. Type I FCoV was found to be predominant compared to type II virus. Results derived from serotyping and genotyping support our current understanding of the evolution of disease-related FCoV and the transmission of FIP. With an immune-mediated disease entity, host genetic variant was suggested to influence the occurrence of FIP. The association between the single nucleotide polymorphisms (SNPs) of tumor necrosis factor-α (fTNFA), DC-SIGN (CD209), and the five FIP-associated SNPs identified from Birman cats, and the outcome of FCoV infection was determined. Among the 57 SNPs identified, five of them, including one in the promoter region of fTNFA, one in the coding region of extracellular domain of DC-SIGN, and three in the introns of CD209 were associated with the outcome of FCoV infections. None of the five Birman FIP cat-associated SNPs showed significant differences between our FIP and non-FIP groups. As disease resistance is multifactorial, the five genetic traits identified in this study should facilitate in the future breeding of the disease-resistant animal to reduce the occurrence of cats succumbing to FIP.

並列關鍵字

feline coronavirus ； feline infectious peritonitis ； type II FCoV ； outbreak of FIP ； baculovirus expressed type specific S protein ； serosurveillance ； host genetic polymorphisms ； tumor necrosis factor-alpha ； C-type lectin DC-SIGN

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