First insight into phylogeography of Mycobacterium bovis and M. caprae from cattle in Bulgaria

Bovine tuberculosis (bTB) represents a significant economic burden to the agriculture. In spite of decades of the control program, Mycobacterium bovis infection levels in cattle in Bulgaria continued to rise over recent years. In order to gain a better understanding of the M. bovis diversity, we used spoligotyping for strain differentiation and the data were compared to the international databases Mbovis.org and SITVIT2 for shared type and clade assignment. Study sample included 30 M. tuberculosis complex isolates from cattle originating from different regions of Bulgaria. The isolates were subdivided by spoligotyping into 4 spoligotypes: 2 types shared by 20 and 8 isolates and 2 singletons. SITVIT2-defined types SIT645 and SIT647 belonged to the common and classical bovine ecotype M. bovis (9 isolates) while types SIT120 and SIT339 belonged to the M. caprae ecotype (21 isolates). A certain phylogeographic gradient of the spoligotypes and clades at the within-country level was observed: M. caprae was prevalent in the central/southwestern, while classical M. bovis in the northeastern Bulgaria. Whereas all four types have global or European circulation, neither was described in the neighboring Balkan countries. M. caprae isolates identified in this study mostly belong to the Central/Eastern European cluster. In summary, this study provided a first insight into phylogeography of M. bovis in Bulgaria and described, for the first time, M. caprae as an important infectious agent of bTB in this country.