Morphological changes of Babesia gibsoni grown in canine red blood cell-substituted severe combined immune deficiency mice

Canine red blood cell-substituted severe combined immune deficiency (Ca-RBC -SCID) mice were prepared for canine Babesia gibsoni infection. The Ca-RBC- SCID mice infected with B. gibsoni developed a high level of parasitemia, a nd showed clinical symptoms such as anemia and hemoglobinuria, which are si milar to those observed in dogs infected with B. gibsoni. The B. gibsoni pa rasites grown in Ca-RBC-SCID mice showed marked morphological changes, incl uding a significantly larger size of parasites than those in dogs and abund ant RBCs containing 4, 8, 16, and 32 parasites. The multiple infection may have resulted from 1 parasite because the posterior end of each parasite in a multiply infected cell was connected. The parasites grown in SCID mice r etained their infectivity and virulence to dogs and their morphology was dr amatically restored to the original state when they were returned to dogs.