The relationship between the age of Schistosoma mansoni cercariae and their ability to penetrate and infect the mammalian host.

The ability of the cercariae of Schistosoma mansoni to penetrate the tails of mice was shown to remain constant throughout their lives. However, their capacity to establish themselves and then reach maturity decreased as they aged. The abdominal route of penetration produced consistently higher maturation rates than the tail route. Significantly different maturation rates were obtained by modifying the standard tail infection technique. Evidence is presented that age-related mortality of schistosomula occurs within 24 h of penetration and may be associated with the exhaustion of energy reserves during the penetration of the stratum corneum. The relationship of this age-related mortality to 'mass mortality' is discussed.