First identification of a Brucella abortus biovar 4 strain from yak in Tibet, China.

Brucellosis is one of the major zoonotic diseases in the world. In China, understanding on its causative agent Brucella is still limited. Recently, we isolated a Brucella strain XZ19-1 from yak in Lhasa, Tibet. Phenotypical characterization proved that it belongs to B. abortus biovar 4, a biotype that has never been reported in China. MLVA-16 genotyping revealed a novel profile (4-5-3-12-2-2-3-3-8-32-8-5-4-3-3-3) in this strain, while MLST sequence typing demonstrated that it belongs to ST 71. Furthermore, the whole genome of XZ19-1 strain was sequenced. Subsequent phylogenetic analysis demonstrated that XZ19-1was genetically more closely related to B. abortus strains originated from European countries rather than to those collected from China previously. Isolation and identification of XZ19-1 strain may thus indicate a unique Brucella lineage existing in Qing-Tibet plateau. These findings will help to improve the diagnosis and epidemiological studies of brucellosis in animals and human in this part of China.