Seroprevalence and Molecular Characterization of Brucella abortus from the Himalayan Marmot in Qinghai, China.

Abstract

Brucellosis is a serious public health issue in Qinghai (QH), China. Surveying the seroprevalence and isolation of B. abortus strains from marmots is key to understanding the role of wildlife in the maintenance and spread of brucellosis. In this study, a set of methods, including a serology survey, bacteriology, antibiotic susceptibility, molecular genotyping (MLST and MLVA), and genome sequencing, were employed to characterize the two B. abortus strains. The seroprevalence of brucellosis in marmots was 7.0% (80/1146) by serum tube agglutination test (SAT); one Brucella strain was recovered from these positive samples, and another Brucella strain from a human. Two strains were identified as B. abortus bv. 1 and were susceptible to all eight drugs examined. The distribution patterns of the accessory genes, virulence associated genes, and resistance genes of the two strains were consistent, and there was excellent collinearity between the two strains on chromosome I, but they had significant SVs in chromosome II, including inversions and translocations. MLST genotyping identified two B. abortus strains as ST2, and MLVA-16 analysis showed that the two strains clustered with strains from northern China. WGS-SNP phylogenetic analysis showed that the strains were genetically homogeneous with strains from the northern region, implying that strains from a common lineage were spread continuously in different regions and hosts. Seroprevalence and molecular clues demonstrated frequent direct or indirect contact between sheep/goats, cattle, and marmots, implying that wildlife plays a vital role in the maintenance and spread of B. abortus in the Qinghai-Tibet Plateau.