<i>Brucella melitensis</i> , a latent “travel bacterium,” continual spread and expansion from Northern to Southern China and its relationship to worldwide lineages

Brucellosis caused by <i>Brucella melitensis</i> is considered to be one of the most important zoonotic diseases in China. In this study, Conventional bio-typing, MLVA (multiple locus variable-number tandem repeat analysis), and WGS (whole-genome sequencing)-SNP (single nucleotide polymorphism) were used to study the genetic similarity of <i>B. melitensis</i> in northern and southern China and analyze its relationship with worldwide lineages. Currently, the distribution of species/biovars of <i>B. melitensis</i> has obviously changed, and <i>B. melitensis</i> has become the dominant species in southern regions of China. Strains from the southern had a common geographic origin with strains from the northern. Many MLVA-16 events were shared in the genotypes of the southern and northern strains, suggest that genotypic movement occurred from north to south. Based on WGS-SNP analysis, strains from different provinces were closely related and may have descended from one common ancestor, suggests that the southern strains originated from northern China. These data indicate that <i>B. melitensis</i> is a latent "travel bacterium" that spread and expanded from North China to South China. Moreover, <i>B. melitensis</i> strains from China are also genetically related to strains from other Asian regions (Kazakhstan, Russia, Mongolia, and India). The movement of infected sheep and their products requires control.