18S rDNA sequences from 4 isolates of Babesia gibsoni originating from Japan, Malaysia and Sri Lanka were compared
with a previously published, 0·5 kb portion of the 18S rDNA from a B. gibsoni isolate from California, USA, and with
the corresponding 18S rDNA sequences of other Babesia spp. Distance, parsimony and maximum likelihood analyses
showed almost identical genotypes among the small canine Babesia from Asia, but an unexpectedly distant genetic
relationship to that from the USA. While the American isolate segregated together with B. equi, the Asian isolates showed
a close relationship to B. divergens and B. odocoilei. These results indicate that small Babesia of dogs originating from
North America and Asia belong to different, genetically distantly related species.