Molecular investigation of infection sources and transmission chains of brucellosis in Zhejiang, China

In the present study, a total of 7793 samples from 5 different types of hosts were collected and tested, with a seroprevalence of 2.4% (184/7793). Although the seroprevalence of human and animal brucellosis is relatively low, numbers of human brucellosis cases reported have increased continuously from 2004 to 2018. A total of 118 <i>Brucella</i> strains containing 4 biotypes were obtained, including <i>Brucella melitensis</i> bv.1 (<i>n</i> = 8) and bv.3 (<i>n</i> = 106), <i>Brucella abortus</i> bv.3 (<i>n</i> = 3) and bv.7 (<i>n</i> = 1). Twenty-one shared MLVA-16 genotypes, each composed of 2 to 19 strains obtained from different hosts, suggest the occurrence of a brucellosis outbreak epidemic with multiple source points and laboratory infection events. Moreover, 30 shared MLVA-16 genotypes were observed among 59.6% (68/114) <i>B. melitensis</i> isolates from Zhejiang and strains from other 21 different provinces, especially northern provinces, China. The analysis highlighted the imported nature of the strains from all over the northern provinces with a dominant part from the developed areas of animal husbandry. These data revealed a potential transmission pattern of brucellosis in this region, due to introduced infected sheep leading to a brucellosis outbreak epidemic, and eventually causing multiple laboratory infection events. It is urgent to strengthen the inspection and quarantine of the introduced animals.

本研究共收集并检测了来自5类不同宿主的7793份样本，血清阳性率为2.4%（184/7793）。尽管人类与动物布鲁氏菌病（brucellosis）的血清阳性率相对较低，但2004年至2018年报告的人类布鲁氏菌病病例数持续攀升。本研究共分离获得118株布鲁氏菌（Brucella），涵盖4个生物型，包括羊种布鲁氏菌（Brucella melitensis）bv.1（n=8）、bv.3（n=106），以及牛种布鲁氏菌（Brucella abortus）bv.3（n=3）、bv.7（n=1）。本次获得的21个共有MLVA-16（MLVA-16）基因型，每个基因型包含2至19株来自不同宿主的菌株，提示存在多源头布鲁氏菌病暴发流行及实验室感染事件。此外，在来自中国浙江的59.6%（68/114）羊种布鲁氏菌分离株，以及国内其他21个省份（尤以北方省份为主）的菌株中，共观察到30个共有MLVA-16基因型。分析结果凸显了北方各省菌株的输入性特征，其中大部分菌株来自畜牧业发达地区。上述数据揭示了本区域布鲁氏菌病的潜在传播模式：引入受感染绵羊引发布鲁氏菌病暴发流行，并最终导致多起实验室感染事件。当前亟需加强引入动物的检验检疫工作。