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.

Schistosoma species detection by environmental DNA assays in African freshwaters

“…It is possible that the use of pre-filtration steps may be required to exclude whole organisms, potentially providing more standardised quantitative spatial and temporal comparisons [33]. Alternatively, it would be possible to modify the environmental DNA methods used here to focus sampling exclusively cercariae [46,47]. Such "qPCR cercariometry" requires relatively large volumes of water (e.g.…”

“…Such "qPCR cercariometry" requires relatively large volumes of water (e.g. 25 litres) that are filtered through a 20μm mesh zooplankton net, before residual material is collected and concentrated allowing qPCR analyses [46,47]. This cercariometry method would allow the collection of large volumes of genetic material from the environment; however such zooplankton nets are expensive and their re-use requires decontamination between sampling events if they are to remain effective.…”

Development of a Molecular Snail Xenomonitoring Assay to Detect Schistosoma haematobium and Schistosoma bovis Infections in their Bulinus Snail Hosts

“…Although able to quantify levels of DNA within a sample, qPCR is more arduous to carry out and lesser suited for use in endemic settings. However, recent technological advances in sample preparation and DNA extraction methods have demonstrated robust field setting methodologies to conduct qPCR analysis capable of detecting avian trematodes and host species in Canadian lakes [ 56 – 58 ], which could potentially be modified to suit the detection of human and bovine schistosomes in sub-Saharan Africa, although cost and throughput would need to be considered.…”

Direct onshore wind predicts daily swimmer's itch (avian schistosome) incidence at a Michigan beach

“…We tested these hypotheses using a dataset of SI reports collected at Congressional Summer Assembly (CSA) Beach on Crystal Lake, Michigan, where the dominant SI parasite is thought to be Trichobilharzia stagnicolae and the dominant host snail is Lymnaea catescopium [ = Stagnicola emarginata; Laman et al, 1984;Correa et al, 2010] (Rudko et al, 2018). While traditional methods for determining SI risk are labour-intensive and require specialized expertise to identify parasites (Kolářová et al, 2010), recent DNA detection and quantification methods are faster and more accurate (Rudko et al, 2018(Rudko et al, , 2019. However, the distinctive rash caused by SI makes it amenable to data collection by citizen scientists, and public beaches have staff (e.g.…”