Temporal human immune response to the avian schistosome cercariae of Trichobilharzia stagnicolae and T. physellae.

Abstract

Swimmer's itch is a human immune reaction to the accidental entrance of an animal schistosome cercaria. The cercaria dies in the skin of the human, causing a small red macule to form within a few hours and a larger, itchier and sometimes puss-filled papule to form within hours to a few days in sensitized individuals. In this study 22 people were exposed to Trichobilharzia stagnicolae cercariae four times over as many weeks and then exposed once to T. physellae cercariae. It was found that 100% of all people are susceptible to contracting swimmer's itch. The average papule size was significantly larger than the average macule size. Macules in people who have never had swimmer's itch before are not significantly different in size from those who have previously had swimmer's itch. Papules in the former group, however, are significantly larger than those in the latter group. There was also a significant increase in papule size from the first exposure to the last in people who have never previously been exposed. Finally, a cross-immunity reaction to the switched cercarial species was observed in people who had never previously had swimmer's itch after four weeks of exposure to the original species.