High levels of congenital transmission of Toxoplasma gondii in longitudinal and cross-sectional studies on sheep farms provides evidence of vertical transmission in ovine hosts

R. H. WILLIAMS a1, E. K. MORLEY a1, J. M. HUGHES a1, P. DUNCANSON a1, R. S. TERRY a2, J. E. SMITH a2 and G. HIDE a1c1
a1 Centre for Parasitology, Molecular Epidemiology and Ecology, Bioscience Research Institute, School of Environment and Life Sciences, University of Salford, Salford M5 4WT, UK
a2 School of Biology, University of Leeds, Leeds LS2 9TJ, UK

Article author query
williams rh   [PubMed][Google Scholar] 
morley ek   [PubMed][Google Scholar] 
hughes jm   [PubMed][Google Scholar] 
duncanson p   [PubMed][Google Scholar] 
terry rs   [PubMed][Google Scholar] 
smith je   [PubMed][Google Scholar] 
hide g   [PubMed][Google Scholar] 


Recent research suggests that vertical transmission may play an important role in sustaining Toxoplasma gondii infection in some species. We report here that congenital transmission occurs at consistently high levels in pedigree Charollais and outbred sheep flocks sampled over a 3-year period. Overall rates of transmission per pregnancy determined by PCR based diagnosis, were consistent over time in a commercial sheep flock (69%) and in sympatric (60%) and allopatric (41%) populations of Charollais sheep. The result of this was that 53·7% of lambs were acquiring an infection prior to birth: 46·4% of live lambs and 90·0% of dead lambs (in agreement with the association made between T. gondii and abortion). No significant differences were observed between lamb sexes. Although we cannot distinguish between congenital transmission occurring due to primary infection at pregnancy or reactivation of chronic infection during pregnancy, our observations of consistently high levels of congenital transmission over successive lambings favour the latter.

(Received March 2 2004)
(Revised August 11 2004)
(Accepted August 17 2004)

Key Words: Toxoplasma gondii; congenital transmission; ovine; abortion.

c1 School of Environment and Life Sciences, Peel Building, University of Salford, Salford M5 4WT, UK. Tel: +0161 295 3371. Fax: +0161 295 5015. E-mail: