Molecular characterization of Mycobacterium bovis isolates from Ethiopian cattle
1 Center for Epidemiology and Biostatistics, Norwegian School of Veterinary Science, P.O. Box 8146, N-0033, Oslo, Norway
2 Department of Veterinary Public Health and Preventive Medicine, Makerere University P.O. Box, 7062, Kampala, Uganda
3 College of Veterinary Medicine, Nursing and Allied Health Sciences, Tuskegee University, Williams-Bowie, Bldg 114, Tuskegee, AL 36088, USA
4 Institute of General Practice and Community Medicine, Faculty of Medicine, University of Oslo, P.O. Box 1130 Blindern, Oslo, Norway
5 Department of Bacteriology and Immunology, Division of Infectious Disease Control, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen N0-0403 Oslo, Norway
6 Department of Animal Health, National Veterinary Institute, P.O. Box 750 dep, N-0106 Oslo, Norway
BMC Veterinary Research 2010, 6:28 doi:10.1186/1746-6148-6-28Published: 27 May 2010
Bovine Tuberculosis (BTB) is a widespread and endemic disease of cattle in Ethiopia. Information relating to genotypic characteristics of Mycobacterium bovis strains affecting the cattle population in Ethiopia is limited. We carried out molecular characterization of M. bovis strains isolated from BTB infected cattle using the spoligotyping technique. The relationship between distribution of spoligotypes and recorded variables was also investigated. A new approach that can numerically reflect the degree of genetic polymorphism in a M. bovis population was also developed. The study was conducted from July 2006 to January 2007 in cattle slaughtered at five representative abattoirs in Ethiopia.
Forty-five M. bovis isolates were obtained from 406 pathologic tissue specimens collected from 337 carcasses with lesions compatible with BTB. Twelve spoligotypes were identified from 34 distinct strains; with SB1176 as a dominant spoligotype (41.2% of the isolates) followed by SB0133 (14.7%). Comparison of spoligotypes with an M. bovis global database http://www.mbovis.org webcite revealed six new spoligotypes which were subsequently registered in the database with international identification codes of SB1517, SB1518, SB1519, SB1520, SB1521 and SB1522. The majority of strains were obtained from cattle slaughtered at Addis Ababa abattoir. On the basis of the Spoligotype Evolutionary Index, SEI (a numeric expression approach to make standardized comparison of spoligotype evolution), M. bovis isolates from Ethiopia were relatively more heterogeneous (SEI = 3.2) compared to isolates from other countries. This might be attributed to extensive livestock movement linked to trading or seasonal migration, high degree of livestock mingling, and also diversities of the country's agricultural and livestock ecosystems, in addition to lack of disease control measures that led to high infection prevalence. Multiple spoligotype infection was recorded in nine (50%) of infected carcasses and this may indicate the prevailing high degree of super infection.
This study provided molecular evidence for the widespread distribution of M. bovis in the cattle population in Ethiopia. It also demonstrated a relatively high degree of genetic polymorphism of the isolates. Further molecular investigation of M. bovis strains in humans and other domestic animals is recommended in order to elucidate the zoonotic importance as well as reservoirs and pattern of transmission among various hosts.