臺灣蚊蟲攜帶棘阿米巴之研究

Abstract

自營性阿米巴廣泛存在於土壤及水中，不需宿主就能在環境中完成其生活史，部分具伺機性感染的阿米巴可以導致人類高致死率的腦膜炎、角膜炎以及皮膚、肺部和鼻竇等感染。巴西研究指出，自營性阿米巴在野生埃及斑蚊 (Aedes aegypti) 的混合樣本中盛行率高達90.0% (54/60)，其中棘阿米巴的盛行率為78.3% (47/60)。而水體環境中的蚊幼蟲是否普遍攜帶自營性阿米巴仍屬未知？根據研究報告：臺灣重要的自營性阿米巴疾病以棘阿米巴為主，而桃園市的阿米巴皮膚膿瘍盛行率高居臺灣各縣市之首，其感染阿米巴種類和造成原因尚待釐清。本研究以桃園市作為調查樣區，自田間採集並分析蚊幼蟲攜帶棘阿米巴的陽性率，以及季節性的變化關係。水溝及小水池之水樣發現有5種棘阿米巴，分別為Acanthamoeba hatchetti (相似度：100.0%；416/416)、A. griffini (相似度：99.5%；417/419)、A. castellanii (相似度：≥ 99.0%；413/417)、A. polyphaga (相似度：98.0%；395/403) 和Acanthamoeba sp. (相似度：99.3%；406/409)。野外蚊蟲調查結果顯示：桃園市蚊幼蟲和蛹的棘阿米巴總體陽性率為9.2% (23/249)，各區分別為平鎮區62.5% (5/8)、桃園區14.6% (6/41)、觀音區14.2% (2/14)、大溪區9.8% (5/51)、楊梅區8.1% (3/37)、龜山區5.0% (1/20) 和龍潭區3.2% (1/31)；蘆竹區 (0/3)、中壢區 (0/7)、大園區 (0/16) 和新屋區 (0/21) 則沒有檢測到棘阿米巴。不同行政區的蚊幼蟲和蛹攜帶棘阿米巴的陽性率有顯著差異 (p=0.005)，而蚊蛹數量為所有樣本的15.7% (39/249)，蚊蛹的陽性樣本有6個。蚊蟲攜帶棘阿米巴的比率依序為家蚊屬12.3% (17/138)、斑蚊屬6.8% (5/73) 和叢蚊屬2.6% (1/38)。其中，家蚊屬的棘阿米巴陽性率在各行政區間有顯著差異 (p=0.003)，斑蚊屬 (p=0.540) 和叢蚊屬 (p=1.000) 則沒有行政區之差異。3種蚊屬的棘阿米巴陽性率也沒有顯著差異 (p=0.133)。棘阿米巴共檢測到23個分離株，分屬三個物種，其中棘阿米巴屬 (Acanthamoeba sp. T4) 及卡氏棘阿米巴 (A. castellanii) 二種對人類有致病性，基因相似度分別為100.0% (419/419) 和99.8% (416/417)，前者的樣本來源為儲水桶水樣，後者的樣本來源為白線斑蚊 (Aedes albopictus) 蛹、熱帶家蚊 (Culex quinquefasciatus) 幼蟲和蛹。本研究採集之7屬成蟲皆未檢出棘阿米巴。在季節性的變化上，蚊蟲攜帶棘阿米巴主要出現在春 (18.8%；6/32)、夏 (9.4%；17/181) 兩季，秋、冬則沒有檢測到棘阿米巴，可能受到秋季前大雨和昌鴻及蘇迪勒颱風影響，四季的陽性率沒有顯著差異 (p=0.084)，但是春季之後陽性率有顯著下降 (p=0.011)。本研究透過蚊蟲檢測出棘阿米巴，於田間從事農務工作者接觸儲水桶內水體後須注意手部衛生。未來應針對蚊蟲可能媒介棘阿米巴的方式進一步研究。

Free-living amoebae (FLA) are ubiquitous in soil and water, and can complete their life cycle without host. These opportunistic microbes can infect human host and cause severe human diseases, such as fatal encephalitis, keratitis, and infections of skin, lung and sinus. Previous study in Brazil indicated that 90.0% (54/60) of pooled samples (10 larvae) of Aedes aegypti larvae were detected with FLA, and 78.3% (47/60) of pooled sample were detected with genus Acanthamoeba. Whether the distribution of FLA in mosquitoes or not is still unknown. According to Taiwan Centers for Disease Control’s reports, the FLA related diseases in Taiwan are mainly caused by Acanthamoeba and the case number of amebic skin abscess was highest in Taoyuan City which compare to other cities with unknown source origin. In this study, mosquito larvae were collected from agricultural fields in Taoyuan City and were detected with Acanthamoeba by molecular method. The positive rate, species gene diversity and seasonal difference of Acanthamoeba were also analyzed. In this study, five species of Acanthamoeba, including A. hatchetti (identity: 100.0%; 416/416), A. griffini (identity: 99.5%; 417/419), A. castellanii (identity: ≥ 99.3%; 413/417), A. polyphaga (identity: 98.0%; 395/403) and Acanthamoeba sp. (identity: 99.3%; 406/409) were identified from water samples in ditch and a small pool. In the field surveillance, the total positive rate of Acanthamoeba in mosquito larvae and pupae in Taoyuan City was 9.2% (23/249). The positive rate in different Districts were 62.5% (5/8) in Pingzhen District, 14.6% (6/41) in Taoyuan District, 14.2% (2/14) in Guanyin District, 9.8% (5/51) in Daxi District, 8.1% (3/37) in Yangmei District, 5.0% (1/20) in Guishan and 3.2% (1/31) in Longtan. Luzhu (0/3), Zhongli (0/7), Dayuan (0/16) and Xinwu District (0/21) were not detected with Acanthamoeba. Positive rate of Acanthamoeba between Districts was significant different (p=0.005). The proportion of mosquito pupae in all samples was 15.7% (39/249). There were 6 positive samples in mosquito pupae. The positive rate of Acanthamoeba in Culex species, Aedes species and Armigeres species were 12.3% (17/138), 6.8% (5/73) and 2.6% (1/38), respectively. Positive rate in Culex between Districts was significant different (p=0.003), but positive rate in Aedes (p=0.540) and Armigeres (p=1.000) was not significant different between Districts. And positive rate of Acanthamoeba between three mosquito genus was not significant different (p=0.133). 23 isolates of Acanthamoeba species were detected in this study. They belonged to three kinds of Acanthamoeba and two of them were pathogenic to human, including Acanthamoeba sp. T4 and A. castellanii. The sequence Identity were 100.0% (419/419) and 99.8% (416/417) respectively. The former were from water sample, and the latter were from pupae of Aedes albopictus, larvae and pupae of Culex quinquefasciatus. Mosquito adults were not detect with Acanthamoeba. Prevalence of Acanthamoeba was mainly in spring and summer, and the positive rate were 18.8% (6/32) and 9.4% (17/181), respectively. Acanthamoeba were not detected in autumn and winter, when heavy rain, typhoon Chan-Hom and Soudelor appeared. There was no significant difference in positive rate of Acanthamoeba between four seasons (p=0.084), but there was a significant decrease after spring (p=0.011). Acanthamoeba were discovered in mosquito larvae and pupae in Taoyuan City. People who working in the agricultural fields need more notice to their hand hygiene after using the water from water containers. The potential dispersal of Acanthamoeba by mosquitoes need further research.