Abstract:
The rickettsial bacterium Ehrlichia ruminantium is the causative agent of heartwater, a serious tick-borne disease in
ruminants. The genetic diversity of organisms in the field will have implications for cross-protective capacities of any
vaccine developed, and for an effective vaccine design strategy proper genotyping and understanding of existing genetic
diversity in the field is necessary. We searched for variable-number tandem-repeat (VNTR) loci for use in a multi-locus
VNTR analysis (MLVA). Sequencing analysis of 30 potential VNTRs using a panel of 17 reference strains from
geographically diverse origins identified 12 VNTRs with allelic profiles differing between strains. Application of MLVA to
38 E. ruminantium-infected Amblyomma variegatum collected from indigenous cattle in 6 different districts of Uganda
identified 21 MLVA types. The discriminatory power of MLVA was greater than that of map1 PCR-restriction fragment
length polymorphism analysis, with which only 6 genotypes were obtained. The high discriminatory power as well as costeffective
performance of MLVA provide the potential for this technique to be applied in the future with respect to
optimizing vaccine trials by identifying local strain diversity, and also raise the possibility of exploring the association
between E. ruminantium genotypes and phenotypes such as pathological outcome in the ruminant host.
