Abstract
To know the infectivity of Babesia microti parasites in dogs, two dogs were experimentally inoculated with B.
microti and parasitemia levels were monitored. Number of erythrocytes gradually decreased until 32 days
after the inoculation and then recovered to normal levels thereafter. Parasites in the erythrocytes were first
observed at 35 days after the inoculation and parasitemia levels reached approximately 1% around 50 days
after inoculation in 2 dogs. Infected dogs showed transiently decreased number of erythrocytes but no
clinical signs during the experimental periods. Smears of the parasitized dog erythrocytes showed positive
reaction with anti-B. microti serum. The PCR assay in parasites DNA from the dogs showed the
amplification of B. microti marker gene and the sequence showed 99% homology with the 16S-like small
subunits from B. microti. These findings show the replication of B. microti in dogs and suggest the
possibility that B. microti is a source of canine babesiosis if the parasite can be transmitted by ticks.
