Abstract
Neospora caninum is considered one of the main causes of abortion in cattle, yet recent studies have also emphasised its relevance as an abortifacient in small ruminants. In order to gain deeper insight into the pathogenesis of ovine neosporosis, pregnant ewes were intravenously inoculated with 106 tachyzoites of the Nc-Spain7 isolate at days 40, 90 or 120 of gestation. Infection during the first term resulted in the death of all foetuses between days 19 and 21 post-infection, showing mainly necrotic lesions in foetal liver and the highest parasite DNA detection and burden in both placenta and foetal viscera. After infection at day 90, foetal death was also detected in all ewes, although later (34–48 days post-infection). In this group, lesions were mainly inflammatory. Foetal livers showed the lowest frequency of lesions, as well as the lowest parasite detection and burden. All ewes infected at day 120 delivered viable lambs, although 3 out of 9 showed weakness and recumbency. Neospora DNA was detected in all lambs but one, and parasite burden was similar to that observed in day 90 group. Lesions in this group showed more conspicuous infiltration of inflammatory cells and higher frequency in foetal brain and muscle when compared to both previous groups. These results highlight the crucial role that the stage of gestation plays on the course of ovine neosporosis, similar to that reported in bovine neosporosis, and open the doors to consider sheep as a valid model for exogenous transplacental transmission for ruminant neosporosis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-014-0139-y) contains supplementary material, which is available to authorized users.
Highlights
Neospora caninum (Apicomplexa: Eimeriina: Sarcocystidae) is an obligate intracellular parasite, which is regarded as one of the most important infectious causes of abortion in cattle worldwide [1]
Foetal death was not detected in control groups; dams from the pregnancy control group (G5) gave birth to healthy lambs between 147 and 150 dg, and foetuses from the negative control group (G4) remained alive just before the euthanasia of their dams on day 20 pi, 40 pi and at parturition
In G3, placenta and uterus could only be recovered from three animals, while in the remaining four animals from this group placentas were too autolytic when recovered after lambing, rendering proper examination impossible
Summary
Neospora caninum (Apicomplexa: Eimeriina: Sarcocystidae) is an obligate intracellular parasite, which is regarded as one of the most important infectious causes of abortion in cattle worldwide [1]. Cattle represent the most relevant and economically important target host, the presence of Neospora infection and transplacental transmission in small ruminants have been previously reported. N. caninum infections in sheep have been reported worldwide [5,6,7,8]. Toxoplasma gondii is regarded as the primary parasite cause for both sheep and goat abortion [1,6,8], and the epidemiological, clinical and economic importance of neosporosis in small ruminants has been traditionally considered to be much less relevant compared to cattle [9,10]. Recently acquired evidence suggests that N. caninum is an important abortifacient in small ruminants [6], or even the main
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