Genetic diversity of Ehrlichia ruminantium based on multilocus sequence typing of isolates from indigenous goats and Amblyomma hebraeum ticks

Heartwater, caused by Ehrlichia ruminantium and transmitted by Amblyomma ticks, remains a major constraint on ruminant production in sub-Saharan Africa. This study investigated genetic diversity of isolates from South African indigenous goats and A. hebraeum ticks using MLST. Screening of 381 goat blood and 70 tick samples yielded 14.7% and 44.3% positives respectively. Sequencing of gltA, groEL, sucA2, and pCS20 identified 11 unique sequence types among 44 sequences (haplotype diversity 0.77). Phylogenetic analyses revealed multiple co-circulating lineages related to Gardel, Kümm2, and Grootvallei, alongside divergent local genotypes. Host-associated structuring was weak (FST = 0.0247), with 97% of variation within host groups, supporting a shared goat–tick transmission system.