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Age-dependent survival and infectivity of Schistosoma mansoni cercariae

Published online by Cambridge University Press:  09 October 2003

P. J. WHITFIELD ,
A. BARTLETT ,
N. KHAMMO  and
R. H. CLOTHIER
P. J. WHITFIELD
Affiliation:
Division of Life Sciences, King's College London, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NN
A. BARTLETT
Affiliation:
Division of Life Sciences, King's College London, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NN
N. KHAMMO
Affiliation:
University of Nottingham, Faculty of Medicine and Health Sciences, School of Biomedical Sciences, Medical School, Queens Medical Centre Nottingham NG7 2UH
R. H. CLOTHIER
Affiliation:
University of Nottingham, Faculty of Medicine and Health Sciences, School of Biomedical Sciences, Medical School, Queens Medical Centre Nottingham NG7 2UH
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Abstract

The age dependency of the mortality, spontaneous de-tailing and infectivity of cercariae of Schistosoma mansoni has been determined at 25 °C. Infectivity was assessed with respect to stratum corneum-like differentiated human keratinocyte cultures (validated by comparison with fresh human skin samples) and displayed a complex age-dependent pattern. From 1 to 9 h post-emergence cercariae showed a plateau of maximal infectivity (around 90% attachment). Thereafter, infectivity declined. Immediately after release, infectivity at around 60% was significantly lower than the plateau values and this could be an adaptation for spatial dispersal of cercariae. Age-dependent patterns of cercarial mortality and spontaneous de-tailing closely mirrored the infectivity pattern except in relation to the low initial infectivity value. These findings suggest that, at a population level, the age-dependent decline in cercarial infectivity towards human skin is essentially driven by cercarial mortality. The recently described phenomenon of delayed tail loss (DTL) in S. mansoni cercariae infecting human skin is confirmed in the present study. For cercariae aged up to 13·5 h post-emergence, 90% or more of invading cercariae took their tails with them into the keratinocyte culture. The infection dynamics described in this study suggest that diurnally shed S. mansoni cercariae, with peak emergence around mid-day, will have near maximal infectivity towards humans in contact with water through all remaining daylight hours in the tropics.

Keywords

Schistosoma mansonicercariaeinfectivitysurvivaltail loss
Type
Research Article
Information
Parasitology , Volume 127 , Issue 1 , July 2003 , pp. 29 - 35
Copyright
2003 Cambridge University Press

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