Expanding the swimmer's itch pool: a first record of Trichobilharzia regenti in Belgium.

Introduction: Swimmer's itch (or cercarial dermatitis) is caused by avian and mammalian blood flukes, a parasitic infection affecting people worldwide. In particular, avian blood flukes of the genus Trichobilharzia, including Trichobilharzia regenti, are known for causing swimmer's itch. While these parasites typically infect waterfowl as final hosts, incidental infections in humans by cercariae can occur. Such infections trigger immune responses leading to painful, itchy skin lesions. In experimental animals, T. regenti has however shown the ability to evade immune responses, causing neuroinflammation. Recent decades have witnessed an increase in swimmer's itch cases across Europe, turning it into an emerging zoonosis. Methods: Following a swimmer's itch case in Kampenhout (Belgium) in 2022, a malacological and parasitological survey was conducted at the transmission site, consisting of a private pond and adjacent creek. Results: Six snail species were collected, including Ampullaceana balthica, a common intermediate host for Trichobilharzia parasites. Shedding experiments and DNA barcoding identified one snail specimen infected with T. regenti, a new species record for Belgium. This finding further strengthens the link between T. regenti and cercarial dermatitis. Additionally, Echinostomatidae sp. and Notocotylus sp. were isolated from other A. balthica specimens. However, the absence of reference DNA sequences hindered genus- and species-level identification for these parasites. Conclusions: The presence of T. regenti in Belgium may have significant clinical implications, emphasizing the need for heightened diagnostic awareness among medical professionals. The lack of species-level identification for other parasite species underscores the need for comprehensive DNA databases for trematodes. These findings reveal the necessity for a Belgian framework to promptly detect and monitor zoonotic outbreaks of trematode parasites within the One Health context.