Trypanosoma lewisi: Termination of pregnancy in the infected rat

Abstract

Trypanosoma lewisi has previously been described as a nonpathogenic parasite of the rat, but these experiments demonstrate that both embryonal and maternal death may occur in the pregnant rat after infection with this parasite. Rats infected early in the first week of pregnancy resorbed their young with little apparent difficulty, and exhibited parasitemia curves typical of nonpregnant infected females of similar age. Rats infected late in the first week of pregnancy experienced greater difficulty resorbing the young, with half of the females dying shortly before parturition. The parasitemia counts were also similar to those of nonpregnant infected rats. The majority of rats infected during the midterm of pregnancy died at the time of parturition, without giving birth to their young. The number of parasites in these animals was abnormally high compared to nonpregnant infected females. Unusually large numbers of dividing trypanosomes were present in the placentae of these animals, many of them containing 8–16 nuclei and kinetoplasts. Animals infected during the last week of pregnancy gave birth to litters of normal size with little apparent difficulty, and had extremely low parasite counts. The hematocrits of all groups of infected animals showed a decrease at the time of peak parasitemia, and the hematocrits of all groups of pregnant rats showed a decrease at the time of birth, except for those infected when day 2 pregnant. These animals completely resorbed their young. The weight losses of rats infected on day 2 and day 6 of pregnancy reflected a termination of pregnancy.