Abstract: Objective  To establish the experimental animal model for the study of Babesia mocroti.  Methods  BALB/c mice, immunosuppressive BALB/c mice, SCID mice and NOD-SCID mice were inoculated with B. mocroti-infected red blood cells（RBC） by intraperitoneal injection respectively. After inoculation, thin blood smears were prepared every day, stained with Giemsa staining and examined for the presence of parasitemia. Three mice were dissected to examine the infectiosity in bone marrow, brain, spleen, heart, lung, kidney and liver tissues. The infection rate of erythrocytes in different tissues was recorded, and the relationship between the infectiosity of tissues and infection rate in peripheral blood was analyzed. Blood samples infected with B. microti were preserved in liquid nitrogen with dimethyl sulfoxide（DMSO） for 2 months. The thawed parasitized blood was injected into the BALB/c mice by same route and the parasitemia was monitored.  Results  The four kinds of mice were all infected by B. microti with parasitemia. The percentage of parasitized red blood cells from peripheral blood were 82.4% （BALB/c mice, d7）, 73.2%（immunosuppressive BALB/c mice, d5）， 86.4% （SCID mice, d8） and 72.5% （NOD-SCID mice, d8） at the maximum, respectively. Parasitemia decreased rapidly in BALB/c mice，　whereas decreased slowly in immunosuppressive BALB/c mice. Only the parasitemia in SCID mice and NOD-SCID mice decreased significantly and tended to picking up again. The parasites were observed in RBCs from bone marrow, brain, spleen, heart, lung, kidney and liver tissues. The infection rate of erythrocytes in tissues increased with an increase of infection in peripheral blood. After cryopreservation, the parasites proliferated in BALB/c mice. Parasitemia appeared after inoculation with frozen infected blood two days later than that of fresh infected blood. The infection rate reached its peak after inoculation with frozen infected blood one day later than that of fresh infected blood.  Conclusion  The experimental animal model of B.　mictoti has been established. The infection rate of erythrocytes is related to the immune status of the host mice.

Key words: Babesia mocroti, Mouse, Animal model