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

In the present study, a total of 7,793 samples from five different types of hosts were collected and tested, with a seroprevalence of 2.4% (184/7,793). 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 four biotypes were obtained, including <i>Brucella melitensis</i> bv.1 (n = 8) and bv.3 (n = 106), <i>Brucella abortus</i> bv.3 (n = 3) and bv.7 (n = 1). Both <i>B. abortus</i> bv.3 and bv.7 were first reported to have been obtained from humans in recent years. <i>B. melitensis</i> was obtained from dogs, sheep blood (food), and laboratory staff members, suggesting that <i>B. melitensis</i> is a crucial threat to the occupational population. Twenty-one shared genotypes, each composed of two to nineteen 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种不同宿主的7793份样本，血清阳性率为2.4%（184/7793）。尽管人畜共患布鲁氏菌病的血清阳性率相对较低，但2004年至2018年期间报告的人类布鲁氏菌病病例数持续攀升。本次研究共分离得到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型（n=8）、bv.3型（n=106），以及牛种布鲁氏菌（*Brucella abortus*）bv.3型（n=3）和bv.7型（n=1）。近年来，牛种布鲁氏菌bv.3型与bv.7型均为首次从人类样本中分离报道。本次研究从犬、羊血（食品）及实验室工作人员样本中分离得到羊种布鲁氏菌，提示该菌对职业暴露人群构成严重威胁。存在21个共有基因型，每个基因型包含2至19株来自不同宿主的菌株，这表明本次布鲁氏菌病疫情存在多疫源点及实验室感染事件。此外，来自中国浙江省的68株羊种布鲁氏菌分离株（占该地区分离株的59.6%，68/114），与中国其他21个省份（尤其是北方省份）的菌株共存在30个共有多位点可变数目串联重复序列分型16（MLVA-16）基因型。分析结果显示，北方省份的菌株均为输入性菌株，其中大部分来自畜牧业发达地区。上述数据揭示了本地区布鲁氏菌病的潜在传播模式：引入带菌羊引发布鲁氏菌病暴发流行，最终导致多起实验室感染事件。当前亟需强化引入动物的检验检疫工作。