Impact ofBabesia microtion the initiation and course of pregnancy in murine model of vertically transmitted infection
Authors: Tołkacz Katarzyna , Rodo Anna , Wdowiarska Agnieszka , Bajer Anna , Bednarska Małgorzata 
Published: October 2020

GenusBabesiagroups tick-transmitted protozoa causing babesiosis, a malaria-like disease. Vertical transmission ofBabesiaspp. 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 ofBabesia microtiin 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 ofB. 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 ofB. microtiin this group was 63% (71/112). In females mated in the acute phase of infection or on the 4thday of pregnancy, no evidence for pregnancy development were observed. In the group infected on the 12thday 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.

AcuteB. microtiinfection 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. ChronicB. microtiinfection 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 congenitalBabesiainfection.

Author summary

The 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, mostlyBabesia microti. Our previous work in murine model proved that vertical transmission ofBabesia 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 ofB. microtiwas 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 intoB. microtivertical transmission will lead to the better understanding of congenital babesiosis.