Impact of Babesia microti on the initiation and course of pregnancy in murine model of vertically transmitted infection

Genus Babesia groups tick-transmitted protozoa causing babesiosis, a malaria-like disease. Vertical transmission of Babesia spp. was reported in mammals, however, the exact timing and mechanisms involved in this mode of transmission are not currently known. In this experimental study we evaluated: 1) the reproductive success, and success of vertical transmission of Babesia microti in mice mated in acute and chronic phases of the infection and in pregnant mice infected during early and advanced pregnancy; 2) possible influence of the pregnancy on the course of parasite infection (parasitaemia) in females; and 3) pathological changes in females and their embryos induced by infection. Blood smears and PCR targeting the 550 bp 18S rRNA gene fragment were used for the detection of B. microti. Histopathological examination was performed on collected tissues. Successful development of pregnancy was recorded only in females in the chronic phase of infection. The success of vertical transmission of B. microti in this group was 63% (71/112). In females mated in the acute phase of infection or on the 4th day of pregnancy, no evidence for pregnancy development were observed. In the group infected on the 12th day of pregnancy, numerous complications including pregnancy loss and stillbirth were recorded. During the acute phase of infection, parasitaemia was lower in pregnant females in comparison to infected, non-pregnant control females. Acute B. microti infection prevents pregnancy initiation and development of pregnancy at a very early stage, and causes severe complication in BALB/c mice in the second and third trimester of pregnancy. Chronic B. microti infection has no negative impact on the initiation and development of pregnancy, but resulted with congenital infections. Further study is required to determine to what extent maternal antibabesial immune responses and potential placental accumulation of parasites contribute to compromised pregnancy in the murine model of congenital Babesia infection. Author summaryThe mouse is the most common mammalian model for studying human parasitic diseases, including malaria, toxoplasmosis, Chagas disease, and babesiosis. Babesiosis is an emerging intraerythrocytic infection caused by protozoal parasites, mostly Babesia microti. Our previous work in murine model proved that vertical transmission of Babesia microti, is a third way - after tick-bite and blood/organ transfusion - to acquire babesiosis. In this study we focused on investigating how the infection influences the course of pregnancy. We were interested in how variations in infection acquisition time and infection phase influence the reproductive success of mice and vertical transmission of parasites. We expected that the infection causes severe pathological changes in the organs of infected females and their offspring. Results obtained in this study have shown that vertical transmission of B. microti was only possible in chronically infected mice, in which health status and reproductive success were not compromised by the infection. Acute infection made successful reproduction impossible, however, the infection had no significant effect on the histopathological condition of tissues. We hope that these insights into B. microti vertical transmission will lead to the better understanding of congenital babesiosis.