Bovine tuberculosis (BTB) remains a major threat to animal and human health, and obstructs
international and inter-regional livestock trade in Ethiopia. Many aspects of epidemiology of BTB and
its causative agent, Mycobacterium bovis (M. bovis) are not well known. Aims of the study were to
elucidate molecular characteristics of M. bovis strains using MLVA typing method. Further aim was to
determine infection pressure associated with occurrence of multiple genotypes in individual infected
cattle. Data and samples were collected in the period July 2006–January 2007 in cattle slaughtered at five
representative abattoirs across the country. Molecular investigation of the isolates was carried out using
multilocus variable-number tandem-repeat analysis (MLVA) of 28 variable numbers of tandem repeat
(VNTR) loci, and the results were compared to spoligotyping. This study is believed to contribute to
the knowledge of molecular genetics and epidemiology of M. bovis in Ethiopia and elsewhere with similar
BTB epidemic situation and livestock production settings. Four-hundred and six tissue samples from 337
carcasses revealing gross pathologic lesions compatible with BTB were collected from five abattoirs.
Fifty-eight isolates obtained from cultured samples were subjected to region of difference (RD) analysis
and MLVA typing. RD confirmed all isolates as being M. bovis. MLVA revealed a high heterogeneity of
M. bovis (19 genotypes) and the discriminatory power of MLVA was higher than for spoligotyping
(Hunter–Gaston Diversity Index (HGDI) 0.92 vs. 0.82). Adoption of the nine VNTR loci with P3 alleles
provided good differentiation between the isolates. However, differentiation was optimized when MLVA
was combined with spoligotyping (HGDI = 0.99). MLVA confirmed infections with multiple genotypes in
38.5% (10/26) of individual animals. In conclusion, the usefulness of MLVA for genotyping M. bovis in high
prevalence settings was demonstrated. BTB in Ethiopia is caused by heterogeneous populations of
M. bovis and individual carcasses were often infected with different genotypes, indicating a high infection
pressure perhaps related to the absence of protective immunity conferred by infection.