綠島硬蜱的分佈以及棲地類型和外來種梅花鹿引入的可能影響

硬蜱會傳播許多人類疾病，不過台灣過去並未針對綠島硬蜱進行深入研究，且過去研究多著重在寄生於動物宿主身上的硬蜱，鮮少調查游離硬蜱；此外，綠島存有不少引入的野生梅花鹿，由於國外許多研究發現鹿為硬蜱相當合適的宿主，因此梅花鹿的引入可能增加當地硬蜱的數量。本研究自2019年1月至2019年12月，選擇草地、森林以及路邊三種棲地類型共31個樣點，包括9個草地、11個森林以及11個路邊樣點，每兩個月進行一次調查，各樣點在清晨和傍晚各進行一次拖行(dragging)採集游離硬蜱，每條樣線長100公尺，寬1公尺。同時設置陷阱捕捉小型哺乳動物，以採集其體外寄生蟲。此外也計算樣線內梅花鹿的排遺堆數以反應其利用程度。六次調查合計記錄到144堆梅花鹿排遺和採集到5,321隻游離硬蜱，包括成蜱124隻、若蜱636隻和幼蜱4,561隻，均屬於血蜱屬(Haemaphysalis spp.)種類。捕捉到126隻小型哺乳動物，分別為2隻溝鼠、24隻小黃腹鼠和100隻臭鼩並採集到48隻硬蜱，總帶硬蜱率為8.7%，其中可辨識種類的27隻硬蜱為粒形硬蜱(Ixodes granulatus)，其餘則均為硬蜱屬(Ixodes spp.)的種類。另外採集到271隻恙蟎，其中可辨識種類的134隻均屬於地里纖恙蟎(Leptotrombidium deliense)。熱點分析結果顯示島東邊的路邊樣線為游離硬蜱之熱點，其次為森林棲地。此外，梅花鹿排遺數與硬蜱數量沒有相關，但棲地類型(P < 0.01)與月份(P < 0.005)均會影響硬蜱數量，且彼此之間有顯著的交互作用(P < 0.001)：整體而言，硬蜱數量在三月與九月的森林和路邊樣線較高，在一月的三種棲地類型以及五、七、九、十一月的草地樣線，數量則是最低。本研究詳細記錄了游離硬蜱在綠島於空間和時間上的變化，並嘗試探討棲地型態和外來種引入的影響，接續將利用分子技術確認硬蜱種類，以及檢測硬蜱感染立克次體屬(Rickettsia spp.)的狀況，對於了解綠島感染硬蜱傳播疾病的風險有相當大的助益。

關鍵字

游離硬蜱；棲地；外來種；蜱媒傳播疾病；綠島

並列摘要

Several human diseases are transmitted by ticks, but there is a lack of studies on hard ticks in Green Island; moreover, past studies in Taiwan have focused on ticks collected from animal hosts, leaving the status of questing ticks unknown. In addition, sika deer (Cervus nippon) are introduced to Green Island and these feral deer might increase the number of ticks given that studies on other countries have demonstrated that deer are a major host of ticks. From January to December 2019, a total of 31 transects (100m x 1m) belonging to three types of habitat, including 9 grasslands, 11 forests, and 11 roadsides, were each dragged at both dawn and dusk to survey questing ticks every two months. Infested ectoparasites were also collected from trapped shrews and rodents in each transect. Lastly, the number of deer pellets observed in each site was deemed as an indicator of extent of deer activity. A total of 144 sika deer pellets and 5,321 Haemaphysalis ticks (124 adults, 636 nymphs and, 4,561 larvae) were recorded. Besides, a sum of 48 Ixodes ticks (27 I. granulatus and remaining unrecognizable Ixodes spp.) were collected from 126 rodents (2 Rattus norvegicus, 24 Rattus losea, 100 Suncus murinus), with 8.7% infestation rate. In addition, a total of 271 chigger mites were recovered, among which the 134 identified specimens were Leptotrombidium deliense. Spatial analyses revealed that roadside habitats in the eastern part of the island and forest habitats in the southern part of the island were the hotspots of ticks. There was no correlation between the number of deer pellets and number of ticks. However, tick abundance was affected by both habitat types (P < 0.01) and months (P < 0.005), and there was an interaction between both factors (P < 0.001). Tick abundance was higher in forest and roadside transects in March and September, but was lower in all habitat types in January, and grassland in May, July, September and November. This study provided a detailed description of variation of ticks across space and time in Green Inland and attempted to associate the variation with habitat types and exotic feral species. My next step is to confirm the tick species with molecular methods as well as assay the infective prevalence of Rickettsia spp. Overall, these results can contribute to a better understanding of human risks to tick-borne diseases in Green Island.