Enzootic situation and molecular epidemiology of <i>Brucella</i> in livestock from 2011 to 2015 in Qingyang, China

A large-scale survey was conducted in domestic animal populations from 2011 to 2015 in Qingyang, China. A total of 448,398 animals from different districts of Qingyang were tested for the presence of <i>Brucella</i>-specific antibodies using the Rose Bengal Plate Test (RBPT) and the Standard Agglutination Test (SAT). From 2011 to 2015, the yearly average positive rates were between 0.04 and 4.75% in the eight counties tested. In addition, the prevalence rates were between 0 and 9.96% in these eight counties. Sheep was the dominant host of <i>Brucella</i> in Qingyang, and the prevalence rate in sheep (2.74%) was higher than those in the other animals tested. Identification of 10 <i>Brucella</i> isolates from sheep confirmed that the epidemic strains were <i>B. melitensis</i> biovar 3 (<i>n</i> = 9) and <i>B. melitensis</i> biovar 1 (<i>n</i> = 1). MLVA-11 (multiple-locus variable-number tandem repeat analysis) analysis of the 10 isolates showed three genotypes: genotype 116 (<i>n</i> = 8), genotype 115 (<i>n</i> = 1) and genotype 136 (<i>n</i> = 1). Furthermore, analysis of the whole-genome sequences of the representative <i>B. melitensis</i> strain QY1 indicated that this isolate was closely related to isolates from China and India. The results of serum epidemiology confirmed that the region of northern Qingyang was a critical <i>Brucella</i> epidemic area and that the disease showed a rising trend, especially from 2013 to 2015. An analysis of the isolate genotypes suggested that sheep brucellosis mainly resulted from conventional <i>B. melitensis</i> (East Mediterranean group), although the external strain (American group) also occurred in Qingyang.