台灣牛結核病的病理變化及菌株基因型分析

Abstract

牛隻的結核菌素檢驗及撲殺政策在台灣至今已施行超過五十年，但每年仍有零星的結核菌素檢驗陽性病例被檢測出來。本研究收集台灣中西部地區的四個牧場、共 57 頭結核菌素檢測陽性的牛隻，進行完整的病理學檢查，分子生物學診斷以及菌株基因型別鑑定。結果顯示，所收集的結核菌素檢測陽性牛中，有 27 頭（47.4%; n = 57）在肉眼或／及顯微檢查下發現有結核樣病灶，其中最常出現病變的位置為咽背淋巴結，其次依序為縱膈淋巴結、肺門淋巴結和腸繫膜淋巴結。透過聚合酶鏈鎖反應檢測，牛型分枝桿菌（Mycobacterium bovis）為引起結核樣病變的主要原因（88.9%; 24/27）。異數重複序列分析（variable number tandem repeat; VNTR）從 15 株牛型分枝桿菌中鑑別出三種不同的基因型別。本研究顯示台灣區的牛隻在長期例行性結核菌素檢驗篩選下，結核病在患畜體內的感染情形，並證實異數重複序列分析能實際運用於台灣地區牛型分枝桿菌基因型別鑑定的檢驗工作。

The campaign against bovine tuberculosis has been carried out in Taiwan based on a principle of test-and-slaughter program for more than 50 years, however, sporadic outbreaks contributed to a fluctuant prevalence of tuberculin test reactors still remained on the present day. A total of 57 cattle with skin test-positive reaction, which originated from 4 individual farms in a central-western county in Taiwan, were slaughtered and sampled for pathologic investigation, molecular diagnosis and bacterial strains genotyping. Tuberculous lesions were identified in 27 cattle (47.4%; n = 57) with the evidence on gross and/or microscopic examination in 1 or more sites. The most frequently affected site was retropharyngeal lymph node, followed by mediastinal lymph node, hilar lymph node, and mesenteric lymph node. Most of the etiologies of these tuberculous lesioned cattle (88.9%; 24/27) were identified as Mycobacterium bovis infection through the PCR assays. Three genotypes of Mycobacterium bovis were found among fifteen skin test positive cattle from three different farms by a molecular genotyping method based on variable number tandem repeat (VNTR) analysis. The findings uncovered the infective status of bovine tuberculosis in the cattle under routine tuberculin test survey, and suggested the application of VNTR to use in distinguish variant strains of Mycobacterium bovis in Taiwan.