Early dynamics of Toxoplasma gondii infection in sheep inoculated at mid-gestation with archetypal type II oocysts.

Early abortion is a clinical presentation of ovine toxoplasmosis that occurs in the second week post-infection (pi), which is characterised by placental infarcts, foetal leukomalacia and absence of parasites in the placenta and foetal tissues. The pathogenic mechanism of early abortion is unknown, and descriptions of the early dynamics of T. gondii infection in pregnant sheep are scarce. The aim of this study was to investigate the presence of lesions and parasite DNA in the small intestine, mesenteric lymph nodes and placenta/foetus, that could be key during the first week after oral infection in sheep at mid-pregnancy. In the small intestine, lesions were rare and parasite DNA detection rates were low (3-8%), with the highest parasite DNA detection and burden found on day 6 pi in the Peyer's patches of the medial jejunum. In the mesenteric lymph nodes, adenomegaly and microscopic lesions were mainly observed on day 6 pi. Parasite DNA was detected in 11% and 61.2% of the samples from mesenteric lymph nodes on days 3 and 6 pi, respectively, with higher parasite DNA detection rates and burdens in the medial and distal jejunal lymph nodes on day 6 pi. In the placentomes, on day 6 pi, gross lesions were not observed, although significant histological changes, such as endothelial activation and vascular thrombosis, were found in 18.6% and 8.3% of the placentomes, respectively. These findings lay the groundwork for future research aimed at elucidating the precise mechanisms underlying early abortions following T. gondii infection in pregnant sheep.