Abstract
The relation between gestational age and foetal death risk in ovine toxoplasmosis is already known, but the mechanisms involved are not yet clear. In order to study how the stage of gestation influences these mechanisms, pregnant sheep of the same age and genetic background were orally dosed with 50 oocysts of Toxoplasma gondii (M4 isolate) at days 40 (G1), 90 (G2) and 120 (G3) of gestation. In each group, four animals were culled on the second, third and fourth week post infection (pi) in order to evaluate parasite load and distribution, and lesions in target organs. Ewes from G1 showed a longer period of hyperthermia than the other groups. Abortions occurred in all groups. While in G2 they were more frequent during the acute phase of the disease, in G3 they mainly occurred after day 20 pi. After challenge, parasite and lesions in the placentas and foetuses were detected from day 19 pi in G3 while in G2 or G1 they were only detected at day 26 pi. However, after initial detection at day 19 pi, parasite burden, measured through RT-PCR, in placenta or foetus of G3 did not increase significantly and, at in the third week pi it was lower than that measured in foetal liver or placenta from G1 to G3 respectively. These results show that the period of gestation clearly influences the parasite multiplication and development of lesions in the placenta and foetus and, as a consequence, the clinical course in ovine toxoplasmosis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-016-0327-z) contains supplementary material, which is available to authorized users.
Highlights
Ovine toxoplasmosis is an important infectious disease caused by the protozoan parasite Toxoplasma gondii, leading to important losses in the sheep industry worldwide due to abortions after primo-infection of pregnant sheep [1]
Despite the fact that the influence of pregnancy on the pathogenesis of ovine toxoplasmosis has been already highlighted [2, 12], the mechanisms responsible for this effect are yet unknown and there are few experimental studies that focused on this aspect of congenital toxoplasmosis, especially in sheep [1]
In order to provide insights into the pathogenesis of ovine toxoplasmosis, in this work an experimental study has been conducted for a detailed comparison of the influence of the stage of gestation on the pathogenesis of the disease
Summary
Ovine toxoplasmosis is an important infectious disease caused by the protozoan parasite Toxoplasma gondii, leading to important losses in the sheep industry worldwide due to abortions after primo-infection of pregnant sheep [1]. This disease is characterized by the presence of multifocal necrotic foci in the placenta and several organs of the foetus, mainly liver and brain, with mild infiltration of inflammatory cells [2, 3]. It is not clear whether the cause of abortion is a direct consequence of the multiplication of the parasite in the foetus or the placenta, or if it is caused by a deregulation of hormones or immune responses in the placenta [1, 7].
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