Parasitology

Research Article

Evidence for high levels of vertical transmission in Toxoplasma gondii

G. HIDEa1 c1, E. K. MORLEYa1, J. M. HUGHESa1, O. GERWASHa1, M. S. ELMAHAISHIa2, K. H. ELMAHAISHIa2, D. THOMASSONa1, E. A. WRIGHTa1, R. H. WILLIAMSa1, R. G. MURPHYa1 and J. E. SMITHa3

a1 Centre for Parasitology and Disease Research, School of Environment and Life Sciences, University of Salford, Salford, M5 4WT, UK

a2 Misurata Central Hospital, PO Box 65 Misurata, Libya

a3 Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK

SUMMARY

Toxoplasma gondii is a highly ubiquitous and prevalent parasite. Despite the cat being the only definitive host, it is found in almost all geographical areas and warm blooded animals. Three routes of transmission are recognised: ingestion of oocysts shed by the cat, carnivory and congenital transmission. In natural populations, it is difficult to establish the relative importance of these routes. This paper reviews recent work in our laboratory which suggests that congenital transmission may be much more important than previously thought. Using PCR detection of the parasite, studies in sheep show that congenital transmission may occur in as many as 66% of pregnancies. Furthermore, in families of sheep on the same farm, exposed to the same sources of oocysts, significant divergent prevalences of Toxoplasma infection and abortion are found between different families. The data suggest that breeding from infected ewes increases the risk of subsequent abortion and infection in lambs. Congenital transmission rates in a natural population of mice were found to be 75%. Interestingly, congenital transmission rates in humans were measured at 19·8%. The results presented in these studies differ from those of other published studies and suggest that vertical transmission may be much more important than previously thought.

(Received June 12 2009)

(Reviewed July 19 2009)

(Accepted July 22 2009)

(Online publication September 21 2009)

Correspondence:

c1 Corresponding author: Geoff Hide, Centre for Parasitology and Disease, School of Environment and Life Sciences, University of Salford, Salford, UK, M5 4WT. Tel: 0044-161-295-3371. Fascimile No: 0044-161-295-5015. E-mail: g.hide@salford.ac.uk

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