Experimental Babesia microti infections in Macaca mulatta: recurrent parasitemia before and after splenectomy.

To learn more about the course of Babesia microti infections in primates, six Macaca mulatta monkeys with blood-induced B. microti infections were followed for 270 days with regular thick blood smears. Three of the monkeys experienced from 1--3 recurrences of parasitemia defined here as greater than or equal to 200 organisms/mm3 blood. Following splenectomy on day 297, parasitemia recurred in all animals, reaching levels of 1.9 x 10(5) to 2.7 x 10(6) organisms/mm3, and was associated with a moderately severe hemolytic anemia. These findings suggest that similar recurrences of parasitemia may occur in human cases, and that splenectomy may present a risk to persons with a past history of B. microti infection.