Species-specific qPCR assays allow for high-resolution population assessment of four species avian schistosome that cause swimmer's itch in recreational lakes

Abstract

Swimmer's itch is an allergic condition that occurs when the motile and infectious stage of avian schistosomes penetrate the skin of an individual. Flatworm parasites that cause swimmer's itch belong to the family Schistosomatidae. They utilize a variety of different species of bird and mammal as definitive hosts, and rely on different species of snail, in which they complete their larval development to culminate in a motile, aquatic, infectious stage called a cercaria. Recently, qPCR-based assays have been developed to monitor for swimmer's itch-causing trematodes in recreational water. This environmental DNA approach has been useful for quantifying the abundance of the free-living cercaria, the causative agent of swimmer's itch. However, the existing qPCR test amplifies from all known schistosome species, making it excellent for assessing a site for swimmer's itch potential, but not useful in determining the specific species contributing to swimmer's itch or the likely hosts (snail and bird) of the swimmer's itch-causing parasites. Thus, species-specific resolution built into a qPCR test would be useful in answering ecological questions about swimmer's itch cause, and efficacy of control efforts. This paper details bird, snail, and cercaria surveys conducted in the summer of 2018, that culminated in the development and deployment of four species-specific qPCR assays, capable of detecting Trichobilharzia stagnicolae, Trichobilharzia szidati, Trichobilharzia physellae, and Anserobilharzia brantae in recreational water. These assays were used to assess the relative abundance of each parasite in water samples collected from lakes in Northern Michigan.

Keywords: Environmental transmission; Recreational water; Schistosoma; Swimmer's itch; Trematodes; Trichobilharzia; eDNA; qPCR.

Graphical abstract

Fig. 1

Abundance of cercariae by sampling site. Water samples were obtained in mid-June and cercariae abundance was determined using the pan-avian schistosomes qPCR.

Fig. 2

Percent contribution of T. stagnicolae, T. szidati, T. physellae and A. brantae species to each lake. Water samples from different locations and dates were tested using the species-specific qPCR assay and results were pooled by lake to understand the relative contribution overall of each species to each lake. The percent contribution (based on gene copy number) of each species was calculated.

Fig. 3

Lifecycles of T. stagnicolae, A. brantae, T. szidati, and T. physellae. life cycle summary of the avian schistosome species targeted for species-specific qPCR tests designed in this study.

SuppFigure1-2.0

Primer and probe locations for each assay. Alignments of the CO1 gene regions with the primer and probe locations for each assay.