Cercaria are infectious larvae of nematodes (trematodes), which develop in snails and, after hatching, infect other intermediate or final hosts. In Central Europe, mainly water birds serve as final hosts, but also humans that are spending time in natural waters can be infected. Although the cercaria die when penetrating the human skin, they can cause an annoying skin inflammation (dermatitis), the so-called cercarial dermatitis or swimmer’s itch. In Central Europe the cercarial dermatitis is caused mainly by cercaria of the genus Trichobilharzia. Traditionally cercaria are detected by collecting water snails, which subsequently are subjected to cercarial hatching experiments. However, this method is very time consuming. In addition, the collection of many molluscs is questionable for nature conservation reasons. DNA barcoding is a promising method for the detection of cercarial dermatitis pathogens in water bodies. This pilot study generated the basis for future investigations by establishing a reference database of DNA barcodes of potential pathogens and their intermediate hosts (freshwater molluscs). In addition, the basis was laid for an environmental DNA (eDNA) approach, in which filtered water samples serve as DNA source for barcoding.

Within the project 10 lakes in Upper Austria were investigated. During 23 excursions a total of 839 water molluscs (23 snail and 7 bivalve species) were collected. During hatching experiments it could be shown that about 15% of the individuals were infected with cercaria. A total of 100 trematode individuals were genetically analysed, whereby 59 COI barcodes were created. This dataset is supplemented by 29 barcodes, which were derived from samples from the NHMW collection material. In the course of the project, Trichobilharzia franki was firstly recorded for Austria, both morphologically and with a DNA barcode. Beyond that, cercariae of the genus Trichobilharzia could only be detected at a single sampling point. For trematodes of the family Echinostomatidae also sequences of the Nd1-marker were generated. 10 DNA barcodes from water snails complete the molecular results. All obtained DNA barcodes will be available on BOLD.

The detection of cercaria using by eDNA was establishedfor the 18S marker up till now. As the sequences are not suitable for the determination on the species level, the marker is only suitable for general trematode detection. Species-specific COI primers for the detection of Trichobilharzia were designed but could not be tested on water samples due to the lack of “cercaria alerts”.

Findings from the project will directly flow into the follow-up project “Sensitivity of eDNA detection of cercaria dermatitis pathogens in Upper Austrian lakes“.