台灣地區犬隻感染巴東體屬細菌之流行病學探討

Abstract

巴東體屬細菌(Bartonella spp.)為近20年來新興的人畜共通傳染病原。本研究針對台灣地區犬隻進行B. vinsonii subsp. berkhoffii(以下簡稱B.v.b)及B. henselae(以下簡稱B.h)病原感染的流行病學調查，探討此兩種巴東體屬細菌在犬隻的感染情形以及可能對人類的威脅性。採集的樣本來源包括有台灣地區流浪犬、門診犬、檢疫犬以及外島義診犬（金門及澎湖）共1630個血液檢體樣本。血清以免疫螢光抗體法(簡稱IFA)檢測，抗體力價≧ 1：64 者判定為血清抗體陽性。血液檢體再進一步以全血培養及PCR快速檢測病原特定核酸片段。研究結果顯示總體血清陽性率B.v.b為4.1%，B. h為4.0%，之中以門診犬族群最高(B.v.b為6.3%；B. h為6.3%)，其次為流浪犬(B.v.b為3.5%；B. h為3.5%)；本島犬陽性率顯著高於外島犬(B.v.b：4.9% vs. 0.6%；B. h：4.9% vs. 0% ) (p<0.05)。檢疫犬方面，僅少數來自泰國(B.v.b為5.7%；B. h為1.9%)和美國(B.v.b為1.3%；B. h為5.2%)的犬隻有檢測出血清抗體陽性。另將B.v.b及B. h 的IFA陽性結果做比較，發現兩者之間有顯著相關。表示此兩種病原可能有共同感染或抗體交叉反應的情形發生。另外在性別、年齡、季節、疾病及犬種因子方面，與抗體陽性狀況無顯著相關。此外在全血培養的結果皆呈現陰性，而經PCR快速檢測，發現有1.9% ( 15 / 796 )的檢體為疑似陽性個案，以上檢體在經過定序及與利用Blast軟體進行與基因庫中細菌DNA序列比對後，發現有部分樣本與來自小型哺乳類動物所分離出之Bartonella spp.相吻合，相似度為96%-100%，有待進一步的探討。綜合以上結果顯示，在台灣地區犬隻中確實有B.v.b及B. h的抗體存在，但感染此兩種病原的血清抗體陽性率偏低(B.v.b：4.1%；B. h：4.0%)，且根據細菌培養及PCR結果推測台灣犬隻可能非B.v.b及B. h 的自然保菌宿主。以目前台灣環境下，此兩種巴東體屬細菌對於犬隻以及傳染給人類的危險性並不大，但根據犬隻來源比較，流浪犬、就診犬以及美國、泰國進口的檢疫犬隻是較為需要注意的易感族群。未來仍應注意人類因意外接觸感染的犬隻而得到此類疾病的風險。

Bartonellae were recognized as emerging zoonoses during the recent 20 years. This study was conducted to understand the epidemiology of Bartonella vinsonii subsp. berkhoffii (B.v.b) and Bartonella henselae (B. h) infections in dogs in Taiwan, and the potential threat to human health. A total of 1630 blood specimens were collected from various sources of dogs in Taiwan, including stray dogs, sick dogs, quarantine dogs and healthy dogs. Indirect fluorescence immunoassay was used for serological testing. Whole blood was tested by culture and direct PCR method. No animals were found to be Bartonella bacteremic, but 15 animals (1.9%) were PCR-positive for Bartonella. After sequencing analyses, the results showed that 3 of the PCR-positive samples were closely related to the sequences of Bartonella spp. previously isolated from small mammals (DNA similarity: 96% - 100%). The seroprevalences of B.v.b and B. h were 4.1% and 4.0% in dogs, respectively. The highest ones were identified in sick dogs (B.v.b 6.3%; B. h 6.3%) and stray dogs (B.v.b 3.5%; B. h 3.5%). The seroprevalences in dogs from the main island were significantly higher than those in dogs from isolated islands (B.v.b 4.9% vs. 0.6%; B. h 4.9% vs. 0%) (p<0.05). In the quarantine population, only several dogs from the United States and Thailand were found to be seropositive. Furthermore, significant association of B.v.b and B. h seropositivity was identified in this study. The possible reasons could be coinfection by these two pathogens or cross-reactivity of serological testings in dogs. By univariate analysis, there was no significant difference of seroprevalences by age, sex, breed, season of collection and clinical status. In conclusion, natural infections of B.v.b and B. h was existing in dogs in Taiwan, but seroprevalences of B.v.b and B. h infections were low and no Bartonella isolates were obtained by blood culture in this study. Therefore, domestic dogs might not be the major reservoir for B.v.b and B. h in Taiwan, and the likelihood of Bartonella spp. transmitted from dogs to humans is thus considered to be low. Nevertheless, people must be aware of acquiring the infections accidentally through dog exposure in Taiwan