臺灣豬隻感染E型肝炎病毒狀況及老鼠所扮演的傳播角色

Abstract

E 型肝炎病毒 (HEV)為經糞口感染非A 型與B 型病毒性肝炎之主要病因。目前，E 型肝炎被高度懷疑為一人畜共通傳染病，豬場飼養管理及豬肉販售相關人員有較一般人高的E 型肝炎抗體的血清陽性率，豬隻被認為是HEV 的重要保毒者，但在已開發國家中，有資料顯示部分E 型肝炎患者並未到豬場或是至HEV 流行地區旅遊的紀錄，顯示可能有其它保毒動物的存在。有研究報告指出，在老鼠可偵測到高血清抗體陽性率，加上老鼠普遍存在於住家、鄉村或豬場環境中，懷疑老鼠在HEV 傳播上扮演另一個重要角色。本研究針對豬隻糞便及老鼠糞便、肝臟及血清檢體，利用反轉錄巢式聚合酶鏈鎖反應（RT-nested PCR）檢測豬隻及老鼠感染HEV 及排毒的情況，並藉由血清學檢測瞭解臺灣老鼠的HEV 血清抗體陽性率。 利用RT-nested PCR 檢測豬隻糞便，由雲林、嘉義、高雄、屏東調查11 個豬場，豬隻依年齡分為哺乳期（1~4 週齡）、保育期（5~12 週齡）、肥育前期（13~18 週齡）、肥育後期（19~24 週齡）及大於1 歲母豬五個年齡階層，HEV 檢出陽性率平均為3.7 % (52/1395)，不同年齡層陽性率以肥育期6.0 % (42/699)較高，其中肥育前期8.2 % (28/352)、肥育後期4.0 % (14/347)。22 個核酸定序成功檢體，16 個屬於第四基因型，另6 個檢體來自同一豬場其HEV 基因序列與流行於歐美國家的第三基因型較為相近。老鼠共檢測血清、肝臟及糞便各128、219 及221 個檢體，RT-nested PCR 皆未檢測出HEV 陽性病例。老鼠HEV 血清抗體陽性率調查，於鄉村、豬場及臺北都會區的陽性率各別為42.0 % (26/62)、 9.1 % (1/11)與7.3 % (4/55)，總計為24.2 % (31/128)，鄉村老鼠的陽性率顯著高於都市老鼠。綜合病毒偵測與血清學調查的結果，老鼠雖曾接觸、感染HEV，但並未檢測出經由糞便排毒的情形，因此推論老鼠應該不是HEV 的重要傳播媒介者，其在豬場內、人類間及豬隻與人類間之HEV 相互媒介傳播上應不會造成大規模的感染。

Hepatitis E virus (HEV) is the major causative pathogen of enterically transmitted non-A and non-B hepatitis in many developing countries and some industrialized countries. A recent survey indicates that HEV may be a zoonotic disease. The possible sources of infection include various animal species, including swine, bovine, deers, and rodents. To investigate the prevalence, viral shedding, and genotypes of HEV infection in pigs in Taiwan, fecal samples were collected from pigs at various ages from different pig farms and evaluated by RT-nested PCR. In addition, samples of feces, liver and serum collected from rodents trapped in pig farms, countryside, and Taipei city were subjected to RT-nested PCR and anti-HEV antibody detection by ELISA to clarify the possible role of rodents on the transmission of HEV within and among pig farms and to humans. A total of 1395 fecal samples were collected from 11 pig farms located in Yunlin, Chiayi, Kaohsiung, and Pingtung. The overall positive rate was 3.7 % (52/1395) and the positive rate of growing pigs was 6.0 % (42/699) and significantly higher than other stages. The PCR products obtained from 22 HEV-positive fecal samples were successfully sequenced. The sequences of 16 positive samples belonged to HEV genotype 4 and the remaining 6 samples were all from one pig farm and were more closely related to HEV genotype 3. A total of 128, 219, and 221 serum, liver, and fecal samples, respectively, were collected from rodents but none of them were HEV-positive by RT-nested PCR. The serum positive rate for anti-HEV antibody in rodents was 24.2 % (31/128) by ELISA. The results suggest that rodents should not be an important source of HEV infection within and among pig farms and to humans. Thus, it is considered that transmission of HEV by rodents should not cause large scale infection whining pig farms, among humans, and between pigs and human.