Abstract
After oral administration of ewes during mid gestation with 2000 freshly prepared sporulated oocysts of T. gondii isolate M4, abortions occurred between days 7 and 11 in 91.6% of pregnant and infected ewes. Afterwards, a further infection was carried out at late gestation in another group of sheep with 500 sporulated oocysts. Abortions happened again between days 9 and 11 post infection (pi) in 58.3% of the infected ewes. Classically, abortions in natural and experimental ovine toxoplasmosis usually occur one month after infection. Few experimental studies have reported the so-called acute phase abortions as early as 7 to 14 days after oral inoculation of oocysts, and pyrexia was proposed to be responsible for abortion, although the underline mechanism was not elucidated. In the present study, all placentas analysed from ewes suffering acute phase abortions showed infarcts and thrombosis in the caruncullar villi of the placentomes and ischemic lesions (periventricular leukomalacia) in the brain of some foetuses. The parasite was identified by PCR in samples from some placentomes of only one sheep, and no antigen was detected by immunohistochemical labelling. These findings suggest that the vascular lesions found in the placenta, and the consequent hypoxic damage to the foetus, could be associated to the occurrence of acute phase abortions. Although the pathogenesis of these lesions remains to be determined, the infectious dose or virulence of the isolate may play a role in their development.
Highlights
Ovine toxoplasmosis is a zoonotic disease of sheep caused by the infection of the protozoan Toxoplasma gondii that results in heavy economic losses for the sheep industry as it is a major cause for reproductive failure
In the current study we report the occurrence of acute phase abortions during an experimental infection of sheep with sporulated oocysts of T. gondii at mid and late gestation
In this study we analyse the main clinical, pathological, parasitological and immunological findings associated with the occurrence of numerous acute phase abortions in experimentally infected sheep after oral inoculation with 2000 or 500 sporulated oocysts of T. gondii M4 isolate
Summary
Ovine toxoplasmosis is a zoonotic disease of sheep caused by the infection of the protozoan Toxoplasma gondii that results in heavy economic losses for the sheep industry as it is a major cause for reproductive failure. Foetal death is thought to be caused by the direct damage of the parasite replication in the foetus, while foetal death later in gestation may result from anoxia caused by extensive necrosis in the placentomes [4]. Lesions in the foetus could be found from day 15 post infection (pi), are more frequent from day 20, affecting the brain, heart, lung and liver. They are characterized by multiple foci of necrosis with an eosinophilic central area that can be surrounded by glial cells in the brain or mononuclear inflammatory cells elsewhere when infection occurs at mid or late gestation [5]. Parasite can be identified in relation to microscopic lesions by immunohistochemical labelling of histological slides or PCR amplification of T. gondii [6]
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