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Animal brucellosis is a re-emerging disease in China with high prevalence in the northwest region. A total of 66 isolates of Brucella were recovered from sheep and yaks in the Inner Mongolia, Xinjiang, Qinghai and Gansu provinces of northwest China in 2015 and 2016. Using classical biotyping and the Brucella AMOS PCR assay, all isolates were identified as Brucella melitensis biovar 3 (n = 58), B. melitensis biovar 1 (n = 1), Brucella abortus (n = 5), or Brucella suis biovar 3 (n = 2), and B. melitensis biovar 3 was found to be mainly responsible for sheep brucellosis in northwest China. Multilocus variable-number tandem-repeat analysis (MLVA) was used to identify the epidemiological relationships among the isolates and to assess their genetic diversity. Multilocus variable-number tandem-repeat analysis-16 identified 46 genotypes in these populations, including 37 unique and nine shared genotypes. Multilocus variable-number tandem-repeat analysis-11 showed that 71% of the isolates (47 of 66) were genotype 116 (1-5-3-13-2-2-3-2-4-41-8), a characteristic subgroup of the East Mediterranean group, showing that isolates from different geographical areas exhibit similar epidemiological characteristics in different regions and may be epidemiologically linked. Multilocus variable-number tandem-repeat analysis-11 also revealed that an isolate from Inner Mongolia had a novel genotype, 369 (1-5-3-13-2-2-3-2-7-41-8). Multilocus variable-number tandem-repeat analysis-16 genotyping of northwest China Brucella isolates allows a better understanding of the epidemiology of animal brucellosis in this region. This study is the first analysis of B. melitensis in Gansu province, and the results confirmed that in this province, isolates of this species are disorderly and unsystematic.

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