台灣家貓冠狀病毒感染之分析 血清型別、感染監測及序列分析

Abstract

摘要 貓冠狀病毒 (Feline coronavirus；FCoV) 為一具有封套之RNA 病毒，依其致病 性可區分為貓傳染性腹膜炎病毒 (Feline infectious peritonitis virus；FIPV) 及貓腸 道型冠狀病毒 (Feline enteric coronavirus；FECV)；依血清型則可區分為第一與 第二型。FIPV 感染多會造成貓隻的死亡，而FECV 則僅引起輕微之消化道症狀， 然兩者之間卻很難經由血清學或實驗室診斷做出明確的區分。本實驗乃藉由巢式 反轉錄聚合酶鏈鎖反應 (RT-nPCR)，針對臨床疑似感染病例進行檢測，並將陽性 的檢體以設計於S 基因引子的RT-nPCR 進行血清型別，來了解各FCoV 血清型 於本土之感染情形。另外，蒐集具有FIP 發病貓之多貓族群，進行其同居貓隻感 染模式的持續監測，並選殖出一本土株FCoV 3’端約9 kb 的序列進行分析。實驗 結果發現，本土家貓所感染的FCoV 以第一血清型為主，佔84.9% (45/53)，而第 二血清型病毒則佔30.2% (16/53)，另外，兩個血清型病毒同時感染的病例也佔有 17.0% (9/53)。統計分析FIP 之發病情況發現第二血清型病毒的感染較第一血清 型病毒更為相關 (P<0.05)，並造成多數感染貓隻的死亡，前者佔87.5%而後者佔 54.3%。在具有FIP 病例發生的多貓家族內，可發現其同居貓隻皆臨床上健康未 出現FIP 的發病，但族群內存有FECV 持續感染的問題，其中部分貓隻可持續排 毒達12 至18 個月以上。有關本土株的序列選殖，本實驗成功地以三個重疊片段 (2.7 kb、2.6 kb 及3.7 kb) 將一糞便來源的FECV 基因體包括有S、3abc、E、M、 N、7ab 及3’UTR 基因增幅選殖出來；根據S 基因的比對結果，此本土株FECV G1-1 屬於第一血清型的病毒，综合S 及N 基因核苷酸比對的結果，推測本病毒 與日本分離株FIPV Ku-2 在演化上最為接近。

Abstract Feline coronavirus (FCoV) is an enveloped RNA virus. According to the pathogenicity of FCoV two distinct biotypes were recognized a feline infectious peritonitis (FIPV) and a feline enteric coronavirus (FECV). Regardless of the biotypes of FCoV both FIPVs and FECVs can further be classified into two distinct serotypes, e.g. type I and II. FIPV is a highly virulent pathogen which induces an immune mediated lethal disease known as FIP, whereas FECV causes only mild enteric syndromes. In the study, RT-nPCR was applied to the detection of FCoVs from the clinical suspected cases. In order to understand the prevalence of FCoV infection in the domestic cats in Taiwan serotyping of the positive specimens with another RT-nPCR targeted to the S gene was performed. The results revealed that among the 53 positive cases 45 (84.9%) were type I, 16 (30.2%) were type II, and 9 (17.0%) were infected with both types. The involvement of type II FCoV infection were found closely associated with the appearance of FIP & hence high mortality rate (14/16；87.5%). The persistence of FCoV infection in the cats living in multiple-cat households that had suffered once loss of cat due to FIP was monitored. The result showed that all cats were clinical healthy and some cats may even persistently shedding virus for at least 12~18 months. To further characterize the local FCoV, three overlapping clones (2.7, 2.6 and 3.7 kb) covering genes from S, ORF3abc, E, M, N, ORF7 to 3’ UTR (about 9kb) from a FECV infected case (G1-1) were generated & cloned. Sequence analysis showed that no nucleotide deletion was present among the 8.9 kb genome region cloned. Furthermore FECV G1-1 was found to be belonged to serotype I and phylogenetic analysis revealed that our local strain is much more similar to one Japanese isolate strain FIPV Ku-2.