貓蚤對系統性殺蟲劑的感受性試驗

Abstract

貓蚤 (Ctenocephalides felis) 是為害貓狗及野生動物的主要外寄生性昆蟲，也會騷擾人類並傳播貓抓病、鼠疫等人畜共通疾病。目前主要以化學藥劑進行防治，而近年來的研究指出貓蚤對常用藥劑已逐漸發展出抗藥性。另一方面，過去有關貓蚤對藥劑感受性的研究多侷限於以成蟲進行測試，而貓蚤幼蟲的感受性研究甚少，且無國際公認的標準幼蟲檢測法。本研究利用 96 孔盤 (96-well plates) 進行單隻幼蟲生物檢測法，針對台灣已經上市和未上市的貓蚤防治藥劑，比較台北市貓蚤品系和實驗室內飼養近二十年的貓蚤品系的幼蟲，在餵食及接觸藥劑的兩種方式下對不同藥劑的感受性，藉此了解系統性殺蟲劑防治貓蚤幼蟲的潛力，並建立未來抗性監測的基礎資料。除此，也就成蟲的藥劑試驗與幼蟲的感受性結果進行討論。幼蟲接觸法結果顯示，貓蚤幼蟲對於市面上常用藥劑芬普尼 (商品名：蚤不到®) 的抗性比 (Resistance ratios, RR = 4.9) 較尚未引進台灣的賜諾殺 (RR = 0.65) 及在台較少使用的益達胺 (商品名：蚤安®) (RR = 1.10) 相對為高；但在幼蟲餵食法則無此明顯差異。此外，由兩種不同幼蟲試驗法，可知賜諾殺適合以餵食的方式毒殺幼蟲，而幼蟲對殺蟲劑的感受性由高至低分別為芬普尼、賜諾殺及益達胺。針對除蚤動物用藥品進行 WHO 成蟲濾紙紙條法感受性測試，得知對益達胺滴劑的感受性高於芬普尼噴劑，而野外品系和實驗室成蟲對兩種商品無感受性的差異。幼蟲接觸法結果意含著台灣野外的貓蚤對於常用防治藥劑的感受性有下降的趨勢；反之，對於不常被使用的藥劑之感受性則無明顯改變。故本研究有關貓蚤幼蟲感受性的試驗結果與台灣用藥情況是吻合的。

The cat flea (Ctenocephalides felis) is a common pet ectoparasite. Besides the discomfort caused to humans, the cat flea may also carry zoonotic organisms. Spraying insecticides on pets and around homes are effective ways to control fleas. Chemical control has been demonstrated to be effective at cutting the flea’s life cycle; however, this may result in rapid development of resistance. There is growing evidence to suggest that fleas have developed resistance to several insecticides. At present, systemic pesticides used for flea control in Taiwan are fipronil and imidacloprid, which are spot-on and spray formulations. Overseas, spinosad in tablet form is currently the latest systemic pesticide in use. We were curious as to whether fleas in the field develop resistance to these newer systemic insecticides over time, therefore, we examined the susceptibility of cat flea larvae and adults from two sources, using a single larval bioassay with 96-well plates (a new technique for detecting flea susceptibility), and WHO filter paper adult bioassay. The first source of cat fleas was from a laboratory colony, and the second from a recent field collection at Taipei animal shelter. The responses to insecticides were different between larvae and adult fleas. Both sources of flea larvae exhibited the lowest susceptibility to imidacloprid and the highest to fipronil. However, adult flea susceptibility to Advantage™ (imidacloprid) was higher than for Frontline®spray (fipronil). The results also indicated that flea larvae had a higher resistance ratio (RR) to fipronil (RR = 4.9) than imidacloprid (RR = 1.10) and spinosad (RR = 0.65). This implies that frequent use of systemic pesticides may reduce susceptibility. Because of this, the susceptibility of cat flea populations to these systemic insecticides should be closely monitored. Detecting flea resistance distribution in the field can help us formulate suitable management strategies to overcome or avoid its effects on flea control in the future.