台灣牧場及口岸蚊媒病原之監測

Abstract

蚊媒性疾病（mosquito-borne diseases，MBDs）為全球熱帶及亞熱帶國家相當重視之議題，其不僅為人類公共衛生上之重要問題，亦是重要的動物疫病問題，造成畜牧業的經濟損失。台灣位於熱帶及亞熱帶交界，為MBDs好發之國家，而登革熱、日本腦炎等疾病更是台灣每年夏季好發之MBDs；除此之外，隨著近年世界高度經濟及貿易發展，台灣成為國際貿易重要樞紐，也大大增加境外移入MBDs之風險。因此，本研究於牛羊牧場及台灣口岸區域進行主動蚊蟲監測，以了解台灣MBDs在蚊子盛行概況以及了解境外移入MBDs之可能性。本研究參考已發表之各重要MBDs分子生物學檢測方法（包含日本腦炎病毒、登革熱病毒、茲卡病毒、黃熱病病毒、西尼羅熱病毒、里夫谷熱病毒、屈公病病毒、瘧原蟲、犬心絲蟲、牛流行熱病毒、藍舌病病毒、赤羽病病毒及施馬倫貝格病病毒），以聚合酶連鎖反應及反轉錄聚合酶連鎖反應等方法，檢測由牧場及口岸區域收集之各類蚊子體內蚊管家基因及MBDs之病原核酸。於民國106年5月至107年3月進行蚊子之收集，在111池共計1151隻蚊子的DNA蚊管家基因陽性的蚊子池中，共有21池蚊子之核酸於PCR檢測呈犬心絲蟲（Dirofilaria immitis）陽性反應，陽性蚊子池包括11池家蚊、4池瘧蚊、5池叢蚊及1池斑蚊，並發現台灣東部及南部收集之蚊子樣本池犬心絲蟲陽性率較台灣北部及中部高。而在57池共401隻蚊子的cDNA蚊管家基因陽性的蚊子池中，有5池蚊子之核酸於RT-PCR檢測呈牛流行熱病毒（Bovine ephemeral fever virus，BEF virus）陽性，這5池BEFV陽性蚊子樣本皆來自於台灣北部，陽性蚊子池樣本分別為4池家蚊及1池瘧蚊，在BEFV核蛋白（Nucleocapsid，N）基因序列親緣關係比較，此5池BEFV陽性樣本具100％基因相似性，並與中國之牛流行熱病毒株最為相近（99％）。另外，在57池cDNA蚊管家基因陽性的蚊子，1池收集於花蓮機場之家蚊蚊子核酸呈藍舌病病毒（Bluetongue virus，BTV）陽性。除了上述三種病原外，台灣地方性蚊媒性疾病病源－日本腦炎病毒、登革熱病毒、赤羽病病毒及台灣未曾發生之七種蚊媒性疾病病原，無論於牧場或是口岸區域之蚊子池，在本研究中皆未檢出陽性反應。本研究於全國各口岸區域及牧場監測重要人畜共通性及動物性蚊媒性疾病，除了解各病原於台灣之分佈及盛行現況外，也監控具境外移入風險之蚊媒性疾病，達到早期警示疾病傳入之作用。

Mosquito-borne diseases (MBDs) represent an important issue not only causing severe public health problems but also resulting in economic losses in the livestock industry in many tropical and subtropical countries. Owing to the geographic location with warm temperature and abundant precipitation, Taiwan is under high risks for the outbreaks of MBDs. Taiwan is also the endemic region for dengue and Japanese encephalitis which occurs nearly in every summer season. Further, due to the rapid growth of human traveling and international commerce activity, the risk of new MBDs invasion into Taiwan by transmissible mosquitoes is increased. The aim of this study was to investigate the prevalence of carrying important Mosquito-borne pathogens in mosquitoes and the risk of transboundary MBDs by collecting and molecular analysis of mosquitoes in the cattle and goat farms, and boundary areas. The primers used were according to the previously published molecular diagnostic method for each Mosquito-borne pathogens(including Japanese encephalitis virus, dengue virus, zika virus, yellow fever virus, West Nile virus, rift valley fever virus, Chikungunya virus, Plasmodium spp., Dirofilaria immitis, bovine ephemeral fever virus, bluetongue virus, Akabane virus, and Schmallenberg virus). Mosquito housekeeping gene (actin-1) was amplified first to confirm the quality of nucleic acid extracted from mosquitoes collected from farms and boundaries and each mosquito-borne pathogens were investigated subsequently by PCR or RT-PCR. The duration of mosquito collection was from May, 2017 to March, 2018. In the total of 111 successful DNA actin-1 amplified mosquito pools obtained from 1151 mosquitoes, there were 21 mosquito pools positive for D. immitis. The positive pools of D. immitis included 11 Culex, 4 Anopheles, 5 Armigeres, and 1 Aedes, separately. The positive rates of D. immitis in the eastern and southern areas are higher than those in the northern and middle areas of Taiwan. In the total of 57 successful cDNA actin-1 amplified mosquito pools collected from 401 mosquitoes, there were 5 mosquito pools positive for BEFV. All BEFV-positive pools were obtained northern Taiwan, including 1 Anopheles and 4 Culex family. Compared with the partial nucleocapsid (N) gene of BEFV, the 5 BEFV positive pools showed 100％ similarity and had nearly 99％ identities with the BEFV strains from China. Besides, there was a Culex mosquito pool colleted from Haulien airports positive for BTV. Aside from D. immitis, BEFV, and BTV, no other aforementioned were detected in either farms or boundaries. The present study has monitored the important zoonotic and animal mosquito-borne pathogens in the farms, airports and harbors in Taiwan. The data provide not only the distribution and prevalence of certain mosquito-borne pathogens in Taiwan but also the field condition of those mosquito-borne pathogens that have not been demonstrated in Taiwan. Thus, the monitoring system should be regularly proceeded.