Direct evidence for preferential multiplication of Babesia gibsoni in young erythrocytes.

To clarify the effect of the age of host erythrocytes on the multiplication of Babesia parasites, B. gibsoni was cultured together with reticulocytes, immature erythrocytes, or mature erythrocytes from dogs. Parasitemia reached peak levels (34.1% +/- 15.8%) at cultivation day 8 in immature-erythrocyte culture, whereas the highest parasitemia attained in mature-cell culture was only 3.6% +/- 2.2% at day 5. These results clearly demonstrate that B. gibsoni parasites preferentially invade and multiply in young erythrocytes rather than in mature cells.