Non-resident definitive host presence is sufficient to sustain avian schistosome populations.

To control swimmer's itch in northern Michigan inland lakes, USA, one species of bird, the common merganser (Mergus merganser), has been relocated from several lakes since 2015. Relocation efforts are driven by a desire to reduce the prevalence of the swimmer's itch-causing parasite Trichobilharzia stagnicolae. The intention of this state-sponsored control effort was to interrupt the life cycle of T. stagnicolae and reduce parasite egg contribution into the environment from summer resident mergansers such that infections of the intermediate snail host Stagnicola emarginata declined. Reduced snail infection prevalence was expected to substantially reduce the abundance of the swimmer's itch-causing cercarial stage of the parasite in water. With no official programme in place to assess the success of this relocation effort, we sought to study the effectiveness and impact of the removal of a single definitive host from a location with high definitive host and parasite diversity. This was assessed through a comprehensive, lake-wide monitoring study measuring longitudinal changes in the abundance of three species of avian schistosome cercariae in four inland Michigan lakes. Environmental measurements were also taken at these lakes to understand how they can affect swimmer's itch incidence. This study demonstrates that the diversity of avian schistosomes at the study lakes would likely make targeting a single species of swimmer's itch-causing parasite meaningless from a swimmer's itch control perspective. Our data also suggest that removing the common merganser is not an effective control strategy for the T. stagnicolae parasite, likely due to contributions of the parasite made by non-resident birds, possibly migrants, in the autumn and spring. It appears likely that only minimal contact time between the definitive host and the lake ecosystem is required to contribute sufficient parasite numbers to maintain a thriving population of parasite species with high host specificity.

qPCR-based environmental monitoring of Myxobolus cerebralis and phylogenetic analysis of its tubificid hosts in Alberta, Canada.

Myxobolus cerebralis is the causative agent of whirling disease in salmonid fishes. In 2016, this invasive parasite was detected in Alberta, Canada, for the first time, initiating a comprehensive 3 yr monitoring program to assess where the parasite had spread within the province. As part of this program, a qPCR-based test was developed to facilitate detection of the environmental stages of M. cerebralis and from the oligochaete host, Tubifex tubifex. During this program, ~1500 environmental samples were collected and tested over 3 yr. Fish were collected from the same watersheds over 2 yr and tested as part of the official provincial monitoring effort. Substrate testing identified sites positive for M. cerebralis in 3 of 6 watersheds that had been confirmed positive by fish-based testing and 3 novel detections where the parasite had not been detected previously. Testing of individually isolated Tubifex from each sample site was used to further confirm the presence of M. cerebralis. DNA barcoding of the cytochrome oxidase I (cox1) gene of 567 oligochaete specimens collected from 6 different watersheds yielded 158 unique sequences belonging to 21 genera and 37 putative species. Phylogenetic analyses of sequences assigned to the genus Tubifex predicted 5 species of Tubifex arising from this assessment. Based on our results, we propose that environmental and worm samples can be a valuable complement to the gold-standard fish testing and will be especially useful for monitoring in areas where fish collection is challenging or prohibitive because of site accessibility or vulnerability of the fish populations.

Evidence of a Putative Novel Species of Avian Schistosome Infecting Planorbella trivolvis.

Freshwater gastropods of the genera Lymnaea Lamarck, 1799, Physa Draparnaud, 1801, Gyraulus Charpentier, 1837, Radix Montfort, 1810, and Stagnicola Jeffreys, 1830 are considered suitable intermediate hosts for avian schistosomes. A large trematode biodiversity survey performed across 3 yr on 6 lakes in Alberta confirmed 3 already-reported snail hosts for 7 North American avian schistosomes; however, the cytochrome c oxidase subunit 1 (COI) nucleotide sequence from 1 cercarial sample (from a single specimen of Planorbella trivolvis) was distinct from all other COI schistosome sequences. As part of a simultaneous, comparable study of P. trivolvis by us in Michigan, we collected another cercarial type from 6 lakes that was 99% similar (COI) to the aforementioned cercarial type. Phylogenetic analyses of the COI and 28S rDNA genes recovered the former cercaria in a clade of avian schistosomes. In Michigan, the feces of a Canada goose (Branta canadensis Linnaeus, 1758) had a miracidium with an identical COI nucleotide sequence. Preliminary swimmer's itch and cercarial emergence studies were performed to determine if the cercariae could cause swimmer's itch and to study the emergence pattern as compared with species of Trichobilharzia Skrjabin and Zakharow, 1920.

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

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.