Enzootic situation and molecular epidemiology of <i>Brucella</i> in livestock from 2011 to 2015 in Qingyang, China

A large-scale survey was conducted in domestic animal populations from 2011 to 2015 in Qingyang, China. A total of 448,398 animals from different districts of Qingyang were tested for the presence of <i>Brucella</i>-specific antibodies using the Rose Bengal Plate Test (RBPT) and the Standard Agglutination Test (SAT). From 2011 to 2015, the yearly average positive rates were between 0.04 and 4.75% in the eight counties tested. In addition, the prevalence rates were between 0 and 9.96% in these eight counties. Sheep was the dominant host of <i>Brucella</i> in Qingyang, and the prevalence rate in sheep (2.74%) was higher than those in the other animals tested. Identification of 10 <i>Brucella</i> isolates from sheep confirmed that the epidemic strains were <i>B. melitensis</i> biovar 3 (<i>n</i> = 9) and <i>B. melitensis</i> biovar 1 (<i>n</i> = 1). MLVA-11 (multiple-locus variable-number tandem repeat analysis) analysis of the 10 isolates showed three genotypes: genotype 116 (<i>n</i> = 8), genotype 115 (<i>n</i> = 1) and genotype 136 (<i>n</i> = 1). Furthermore, analysis of the whole-genome sequences of the representative <i>B. melitensis</i> strain QY1 indicated that this isolate was closely related to isolates from China and India. The results of serum epidemiology confirmed that the region of northern Qingyang was a critical <i>Brucella</i> epidemic area and that the disease showed a rising trend, especially from 2013 to 2015. An analysis of the isolate genotypes suggested that sheep brucellosis mainly resulted from conventional <i>B. melitensis</i> (East Mediterranean group), although the external strain (American group) also occurred in Qingyang.2011年至2015年，中国庆阳市针对家畜种群开展了一项大规模流行病学调查。共计采集庆阳各区县的448398头（只）动物样本，采用虎红平板凝集试验（Rose Bengal Plate Test, RBPT）与标准试管凝集试验（Standard Agglutination Test, SAT）检测布鲁氏菌（Brucella）特异性抗体。2011至2015年间，8个受检区县的年均阳性率介于0.04%至4.75%之间；各区县的布鲁氏菌流行率范围为0至9.96%。绵羊为庆阳市布鲁氏菌的主要宿主，其布鲁氏菌感染率达2.74%，高于其余受检动物。从绵羊中分离得到的10株布鲁氏菌经鉴定，流行菌株为羊种布鲁氏菌3生物型（B. melitensis biovar 3，n=9）与羊种布鲁氏菌1生物型（B. melitensis biovar 1，n=1）。对这10株分离菌开展MLVA-11（多位点可变数目串联重复序列分析，multiple-locus variable-number tandem repeat analysis）分型，结果显示存在3种基因型：基因型116（n=8）、基因型115（n=1）及基因型136（n=1）。此外，对代表性羊种布鲁氏菌菌株QY1的全基因组序列分析表明，该分离株与中国及印度的分离株亲缘关系紧密。血清流行病学结果证实，庆阳市北部区域为布鲁氏菌重点流行区，且该病呈上升趋势，尤以2013年至2015年期间为甚。分离菌基因型分析显示，绵羊布鲁氏菌病主要由经典羊种布鲁氏菌（东地中海群）引起，但庆阳市也存在外来菌株（美洲群）。