High levels of congenital transmission of Toxoplasma gondii in a commercial sheep flock

https://doi.org/10.1016/S0020-7519(01)00282-XGet rights and content

Abstract

Our current understanding of congenital transmission of Toxoplasma gondii from ewe to lamb dictates that infection frequently results in abortion and the death of the developing foetus, that the birth of live infected lambs occurs rarely and that the cat is the predominant source of infection in ewes. Using direct polymerase chain reaction detection of T. gondii, we report high levels of congenital transmission occurring in a commercially managed sheep flock. We sampled foetal-derived placental tissue and tissues from aborted lambs and showed that congenital transmission was detected in these tissues from 61% of all pregnancies. Where pregnancies resulted in the death of one or more lambs, T. gondii was detected in the lamb tissue for all but one of 18 (94%) pregnancies. Of the successful pregnancies resulting in the birth of live lambs we were able to detect T. gondii in foetal-derived placental tissue from 37 of 70 (42%) pregnancies. These results show that congenital transmission is occurring in a high percentage of lambings including normal healthy lambings, at this farm, suggesting that this route of transmission from generation to generation may be much more significant than that reported previously. These results may have implications for sheep husbandry and future epidemiological studies of T. gondii.

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Acknowledgements

We would like to thank the University of Salford, The Wellcome Trust and the Yorkshire Agricultural Society for funding. We gratefully acknowledge the contribution of Allan Maiden and family to this research.

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      Citation Excerpt :

      Transplacental or congenital transmission is the most frequent and severe form of transmission, with natural spread in the acute or acute relapse of chronic disease during pregnancy [27]; thus, the disease spread is inevitable in flocks with the presence of positive animals. Duncanson et al. [28], while detecting T. gondii DNA from aborted lambs of a commercial sheep flock, found high levels (94%) of transplacental transmission. In lambs born alive, 42% were seropositives for T. gondii, which represents lower levels compared to those found in this study (68%).

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