Molecular characteristics of Brucella strains and epidemiological characteristics of human brucellosis in Ulanqab, Inner Mongolia, 2004−2021

  Objective  To analyze the epidemiological characteristics of human brucellosis in Ulanqab, Inner Mongolia, from 2004 to 2021, and provide theoretical support for the development of human brucellosis prevention and control strategies in this area.

  Methods  The number of cases, incidence rate, and composition ratio of human brucellosis were used to describe the characteristics of the epidemic. The strains isolated in 2016 in this region were identified and genoryping by AMOS-PCR and MLVA assay. Moreover, based on the MLVA-16 typing approach, the strains in this study were compared with Brucella melitensis from the international Brucella MLVA database to investigate the molecular epidemiological relationship between the strains.

  Results  The prevalence of human brucellosis in Ulanqab increased year by year from 2004 to 2011, reaching its peak in 2011, showed a decline trend from 2012 to 2108 and increased again during 2019−2021. From 2004 to 2021, a total of 29 713 human brucellosis cases were reported in this area, with 1,650 cases being reported in each year and an average annual incidence rate of 75.46/100 000. The prevalence of human brucellosis in the back mountain area of Ulanqab was significantly higher than that in the front mountain area. The identification by two molecular methods (AMOS-PCR and MLVA-8) showed that the 22 strains isolated were all Brucella melitensis, and the strains belonged to the Eastern Mediterranean lineage. These strains had high genetic similarity (80%−100%), suggesting a single common ancestor. Likewise, the 20 strains from this study had complete identical MLVA-16 genotype with the previous isolates in this area and in other areas, respectively, indicating that the strains can not only spread in the area in the future but also has the characteristics of cross-regional or cross-border spread.

  Conclusion  The human brucellosis epidemic in Ulanqab has been controlled to a certain level, but the epidemic is still serious. There is a risk of epidemic importation or exportation, so it is suggested to strengthen the control of the source of infection (infected sheep) for the prevention of human brucellosis.