環境變遷以及不同尺度環境因子與宿主群聚對於節肢動物病媒的影響：以恙蟎為例

The effect of environmental change, environmental factors at different scales and host assemblage on arthropod disease vectors: A case study of chiggers

朱家瑩(Chu Chia-Ying)

指導教授 ： 郭奇芊

國立臺灣師範大學/理學院/生命科學系/碩士(2022年)

https://doi.org/10.6345/NTNU202201717

摘要

人類感染病媒傳染病的風險，和病媒的數量有關，而病媒數量除了受到環境因子控制外，亦會受到宿主種類影響，某些宿主種類能提供病媒較營養的食物來源。恙蟲病為由恙蟎幼蟎所傳播的立克次體疾病，主要流行於西太平洋地區，包括臺灣。恙蟎的生活史主要包括卵、幼蟎、若蟎和成蟎四個時期，幼蟎為寄生性，主要宿主為齧齒類動物，若蟎和成蟎則行自由生活，以土壤中其他節肢動物為食。本研究旨在探討兩個問題：一是不同尺度的環境因子，包括小尺度的微棲地特徵和較大尺度的土地利用，以及老鼠種類，如何影響花蓮－恙蟲病流行地區－的幼蟎數量，包括外來種緬甸小鼠入侵的可能影響；二是環境變遷對於該地區的幼蟎數量與當地的老鼠寄生恙蟎狀況的影響。2020-2021年於花蓮不同棲地環境的64個樣點，每樣點設置39個捕鼠籠連續捕捉老鼠3晚(共7,488個籠夜)，並計數老鼠身上寄生的幼蟎數量，同時測量每個樣點內30個捕捉籠位分別的微棲地特徵，以及計算樣點半徑一公里內的土地利用狀況和人口數。本研究基於人口密度的差異，將樣區分為人為干擾程度相對較高的北部區域(包括花蓮市、吉安鄉以及壽豐鄉中部以北的區域)以及干擾相對較低的南部區域(包括壽豐鄉中部以南至鳳林鎮的區域)。結果顯示緬甸小鼠和赤背條鼠分別是北部和南部區域最常捕捉到的種類。南部區域每樣點可採集到的恙蟎數量約為北部區域的25倍，數種恙蟎主要宿主的恙蟎寄生量也以南部區域顯著較北部區域高。恙蟎種類以英帕恙蟎(Leptotrombidium imphalum)(95.43%)為主。分析恙蟎數量與微棲地、土地利用和動物宿主數量的關係，發現區域會顯著影響恙蟎數量，恙蟎數量也和樹林面積以及小黃腹鼠、赤背條鼠的數量呈正相關，而旱田面積、田和植被鑲嵌面積以及緬甸小鼠數量在不同區域對恙蟎數量有不同的影響，微棲地則無顯著的影響。與2007-2008年在相同季節，採用相同捕捉方式的46個樣點相比，2020-2021年時恙蟎數量在南北兩區域均顯著變少，尤其是在人為干擾程度較嚴重的北部區域，推論可能與宿主數量減少以及環境改變有關。南部區域恙蟎數量的減少無法確定是否導因於緬甸小鼠的入侵，這是由於2007-2008年至2020-2021年間，還伴隨著棲地環境的改變，同時也會影響恙蟎的數量。本研究顯示人為干擾會顯著降低恙蟎的數量，日後研究應該同時探討土壤特性對於恙蟎的可能影響以及釐清緬甸小鼠與其他原生種齧齒類動物宿主的關係，以得知緬甸小鼠入侵是否會如何影響恙蟎的數量。

關鍵字

病媒傳染病 ； 恙蟎 ； 人為干擾 ； 微棲地 ； 土地利用

並列摘要

Human risk to vector-borne diseases is associated with number of vectors, which could be influenced by environmental factors and host assemblage. Scrub typhus, a vector-born disease caused by the rickettsia Orientia tsutsugamushi and transmitted by larval trombiculid mites, is prevalent in the western Pacific, including Taiwan. The life cycle of trombiculid mites involves four main stages: egg, larva (chigger), nymph and adult. Nymphs and adults are free-living while chiggers are parasitical and rodents are the main hosts. This study aims to investigate how environmental factors of different spatial scales (microhabitat and surrounding land use) and host species, including the invasion of Rattus exulans, would affect chiggers in Hualien of eastern Taiwan, a hotspot of scrub typhus. In addition, the effect of environmental change on chiggers was also be investigated. A field survey including small mammal trapping, chigger collection, microhabitat measurements, and inventory of land use and population density within 1-km radius was conducted at 64 sites in Hualien between September 2020 to March 2021. Each site was deployed with 39 traps for 3 consecutive nights (totaling 7,488 trap-nights), and chiggers were collected from trapped small mammals. I also divided the study area into northern and southern regions based on the difference in population density, with more human disturbance in northern than southern region. The results showed that R. exulans and Apodemus agrarius were the most common species in northern and southern regions, respectively. The number of chiggers per study site in southern region was 25 times that in northern region. Chigger loads of several major chigger hosts were significantly higher in southern than in northern regions. Leptotrombidium imphalum was the most common chigger species (95.43% of all identified chiggers). The number of chiggers was affected by region, area of forest, number of R. losea and number of A. agrarius. Besides, effect of area of rainfed cropland, area of natural vegetation/cropland mosaic, and number of R. exulans on chiggers varied with regions. Microhabitat had no effect on chiggers. Between 2007 and 2008, 46 sites were surveyed in Hualien with the same sampling design and in the same seasons. Number of chiggers was significantly lower in 2020-2021 than in 2007-2008 in both regions, particularly in northern region with more human disturbance. Such reduction in the number of chiggers was likely related to the reduced number of hosts and environmental change. It cannot be confirmed that the decreasing number of chiggers in southern region was attributed mainly to the invasion of R. exulans. This is due to that, from 2007-2008 to 2020-2021, environmental change which can also affect chiggers through effect on soils also occurred. This study demonstrates the suppressive effect of human disturbance on chiggers. Further studies could investigate how properties of soil would affect chiggers. Additionally, elucidating interactions between R. exulans and other rodent species would help reveal the potential effect of R. exulans expansion on chiggers.

並列關鍵字

vector-borne disease ； chigger ； human disturbance ； microhabitat ； land use

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