A study of the death of Schistosoma mansoni cercariae during penetration of mammalian host skin: The influence of the ages of the cercariae and of the host

A study of the death of Schistosoma mansoni cercariae during penetration of mammalian host skin: the influence of the ages of the cercariae and of the host. International Journal for Parasitology 3: 789–794. The number of cercariae of S. mansoni which die during penetration of mouse abdominal skin steadily increases with age following emergence from the snail. An initial mortality level of about 30 per cent is observed for 2-h-old cercariae which rises to 50 per cent at 8 h and 85 per cent at 24 h. These increased losses in the skin are shown to account substantially for the known decrease in infectivity which accompanies ageing of cercariae. The number of cercariae which die in the skin of very young mice (2 days old) is less than one-third of the level in adult mice. Losses in the skin increase with age of the host up to about 28–35 days. This increased mortality in the skin is shown to account for the observed age resistance of mice, where fewer cercariae mature into adult worms in mice of 1 month or more, than in very young mice.