Genotypic diversity in Babesia bovis field isolates and vaccine strains from South Africa.

Genotypic diversity in Babesia bovis (cause of Asiatic redwater in cattle) vaccine strains and field isolates from South Africa were investigated using the Bv80 gene as well as microsatellites. The S11 vaccine strain possessed both A and B alleles of the Bv80 gene, as well as genotypic diversity within each allele type as defined by repeat variation resulting in different amplicon sizes. Rapid serial passage of vaccine strain from passage S10 to S24 resulted in loss of genotypic diversity that yielded a single allele A genotype with an amplicon size of 558 bp. This suggested that clonal selection occurred during rapid passaging. Extensive genotypic diversity exists in 44 field isolates characterized with both Bv80 A and B alleles, but can be readily distinguished from the S24 vaccine strain using either the Bv80 allele specific PCR assays or using multi-locus micro-satellite typing. This indicated that no recent documented clinical cases of Asiatic redwater were caused by the reversion to virulence of the current vaccine strain.