Discussion

Human cercarial dermatitis (CD) or cercariosis is a cutaneous allergic response caused by repeated penetration of avian and mammalian schistosome cercariae and possibly non-schistosomatid cercariae. It is an emerging and re-emerging disease frequently reported in Europe and the USA in association with recreational lakes inhabited by snail intermediate hosts and waterfowl definitive hosts for Trichobilharzia spp. There is insufficient information about the occurrence and causative agents of CD in the UK and the condition is under-diagnosed due to confusion with insect bites and lack of a reporting system. Reports of CD in the UK are increasing in frequency via social media, partly due to the popularity of open water swimming, although the full extent of CD as a health issue is not known. This is the first study in the UK to explore occurrence of CD and its impacts on open water swimmers. Following ethical approval from Kingston University Ethics Committee, open water swimmers were contacted via swimming clubs and on social media to complete a 14-question survey on Survey Monkey on CD and open water swimming behaviour during 2016. A total of 62 responses (61% female: 39% male, age range: <25 to >76) were received. Self-diagnosed reports of CD were recorded from 38 sites, mainly in England, comprising freshwater lakes and rivers except for one marine site in Cornwall. Interestingly, not all swimmers experienced symptoms at known CD sites and they reported symptoms from April to November, beyond the usual seasonal period of cercarial emergence.  CD does not discourage open water swimming for the majority due to strong motivators for the sport. Multiple preventative measures and treatments were undertaken, mainly following advice from friends, pharmacies and the internet. Wet suits were not worn by the majority and do not appear to be effective in preventing CD. The efficacy of removing snail intermediate hosts at one site is currently being tested and more demographic data will be needed in future studies to identify reasons for variable responses to exposure.