The blood picture resulting from Nuttallia (= Babesia) rodhaini and Nuttallia (= Babesia) microti infections in rats and mice

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Abstract
The parasitaemia and associated blood picture following infections of Nuttallia rodhaini in rats and mice, and N. microti in rats are described. After inoculation of the blood stages of these parasites, it is evident that only further blood stages occur in the host animal. Infections with both piroplasms follow a similar course, there being a prepatent period followed by a patent infection which reaches a peak and then disappears. The prepatent period is an artifact due to the rarity of the parasites in the peripheral blood. The patent infection of N. rodhaini in rats and mice rapidly reaches a peak of up to 90% R.B.C. infected. That of N. microti develops more slowly and rarely reaches 20%. Rats show age resistance to both piroplasmoses but none is shown by mice aged up to 1 year against N. rodhaini infection. Increase of the parasite inoculum dose decreases the prepatent period and also the time from infection to the peak. In rats there is a corresponding increase of the peak but in mice this remains constant. N. microti infections in rats are enhanced by splenectomy, the peak being higher but the time from infection to the peak not altering. The parasitaemia produced by both piroplasms results in a temporary anaemia and reticulocytosis. The anaemia is not prolonged which does not suggest autoimmune reactions. Both piroplasms preferentially invade reticulocytes as compared with mature erythrocytes although this is apparently reversed at the onset of reticulocytosis.An explanation of the mechanism of the parasitaemia of the piroplasms in rats and mice is suggested.This paper is a report of work carried out in part for a thesis submitted for the degree of Ph.D. in the University of London. The work was aided by an S.R.C. research studentship. I would like to thank Dr F. E. G. Cox for his supervision and also for performing the splenectomies.