囓齒動物外寄生蟲印度鼠蚤感染鼠型斑疹傷寒立克次體及貓立克次體之分子檢驗

Abstract

由跳蚤傳播的地方性斑疹傷寒立克次體 (Rickettsia typhi) 所引起的地方性斑疹傷寒 (Murine typhus)，在臺灣已發現一個多世紀，但監測幾乎完全依賴於人類臨床病例的發現，而維持囓齒動物與人類之間傳播的病媒蚤在臺灣從未進行過系統性的分子檢驗。本研究旨在釐清環境中病媒蚤的立克次體陽性率，以嘗試填補此知識缺口。取 2023 年 2月至 2024 年 10 月間，自全島鼠型動物體外寄生蟲之調查中所收集的印度鼠蚤 (Xenopsylla cheopis) 進行橫斷性分子檢驗。這些跳蚤之鼠型動物宿主來自 23 個地點中的 30 個採樣點，共有溝鼠 (Rattus norvegicus)、錢鼠(Suncus murinus)、亞洲家鼠 (Rattus tanezumi) 三種動物宿主。將來自 167 隻鼠型動物宿主的 780 隻印度鼠蚤，根據宿主將樣本分成 167 個混合樣本，並對其中 336 隻跳蚤個體以聚合酶連鎖反應 (PCR) 進行分子檢驗。採用三基因 PCR 流程，COI 作為核酸萃取物的對照目標基因、gltA 為立克次體篩檢廣用基因以及以 ompB 作為二次篩選與後續定序的目標基因。陽性樣本再以 Sanger 定序法獲得核酸序列，並與 NCBI 之基因資料庫以 BLAST 法比對。結果顯示在 167 個混合樣本中，有 164 個池 (98.2%) 的 COI 基因被成功擴增以確認核酸萃取成功。然在任何地點、宿主或時間中，均未檢測到屬於 R. typhi 的 gltA 或 ompB 基因，因此未計算最小感染率 (Minimum Infection Rate)。僅有一個來自高雄之錢鼠的混合樣本 (CY23-28) 呈現陽性，經序列比對鑑定為貓立克次體 (Rickettsia felis)。在本研究中所有混合樣本的傷寒立克次體檢測結果均為陰性，這與臺灣有較低的地方性斑疹傷寒感染率 (約 0.11/100,000) 一致，亦與國際跳蚤調查中跳蚤對傷寒立克次體感染率普遍低於貓立克次體的現象相符；且貓立克次體的檢出證實檢測方法的靈敏度無疑。本研究首次在臺灣對印度鼠蚤進行全島範圍內的傷寒立克次體之系統性分子檢驗，並建立一個可重複檢驗的病媒水準基線和篩檢流程，以支持未來在台灣進行蚤媒立克次體病的綜合監測。 關鍵詞：地方性斑疹傷寒、傷寒立克次體、印度鼠蚤、蚤媒立克次體病、病媒監測、台灣、貓立克次體。

Murine typhus, caused by the flea-borne bacterium Rickettsia typhi, has been recognized in Taiwan for more than a century, yet surveillance has relied almost entirely on human clinical case detection, and the flea vectors that maintain transmission between commensal rodents and humans have never been screened systematically by molecular methods in Taiwan. This study addresses that gap with a cross-sectional molecular survey of Xenopsylla cheopis fleas archived from islandwide rodent and ectoparasite surveillance between February 2023 and October 2024. A total of 780 X. cheopis fleas from 167 small mammal hosts spanning 30 site-visits across 23 localities and three host taxa (Rattus norvegicus, Suncus murinus, and Rattus tanezumi) were pooled by host into 167 pools, of which 336 fleas were tested, and subjected to a sequential three-gene PCR pipeline (CO1 extraction control, gltA primary Rickettsia target, and ompB secondary screen and sequencing target), with positive amplicons confirmed by Sanger sequencing and BLAST. Extraction was confirmed by CO1 amplification in 164 of 167 pools (98.2%). No pool produced a confirmed R. typhi amplicon at gltA or ompB in any geographic, host, or temporal stratum; a single pool (CY23-28, from a Suncus murinus host in Kaohsiung) was sequence-confirmed as Rickettsia felis, and because no pool was positive no Minimum Infection Rate was calculated. This all-negative R. typhi result is consistent with Taiwan’s low human incidence (approximately 0.11 per 100,000) and with the characteristically low per-flea R. typhi prevalence and predominance of R. felis in flea surveys internationally; the R. felis detection confirms assay sensitivity. This study provides the first islandwide, systematic molecular screen of Xenopsylla cheopis fleas for Rickettsia typhi in Taiwan and establishes a reproducible vector-level baseline and screening pipeline to support future integrated surveillance of flea-borne rickettsioses in Taiwan. Keywords: murine typhus; Rickettsia typhi; Xenopsylla cheopis; flea-borne rickettsioses; vector surveillance; Taiwan; Rickettsia felis.