Examination of the diversity and assembly processes of digenean trematode communities in Alberta, and the implications of spatio-temporal community dynamics on swimmer's itch transmission in recreational lakes

• Author / Creator

  Gordy, Michelle Ann

• The preservation of biodiversity on our planet is crucial to our health. However, we cannot preserve what we do not understand. Biodiversity surveys most often forget to include some of the most diverse organisms on our planet, the parasites. Historically given a bad rap because of the diseases they can cause, parasites are often not thought of as organisms we should preserve. What most do not realize is that parasites are engrained in food-webs and ecosystems, playing many different important roles in the processes that regulate populations and more. Parasites can also form their own communities, and the processes that underly their assembly can have important impacts on the transmission of certain diseases. The focus of my doctoral research has been to examine the diversity and assembly processes of digenean trematode communities in Alberta, and the implications of community dynamics on their transmission of in recreational lakes. Trematodes are parasitic flatworms that have complex life cycles involving two or more host species. Some of the underlying factors that can affect trematode community assembly in their snail hosts are environmental factors that relate to the quality of the ecosystem, and therefore the suitability for their hosts. As well, the ecological interactions, those occurring between species, such as competition and predation, can impact community assembly as well. So, if we have an understanding of how trematode communities are formed, we may predict how changes to the important factors may impact the transmission of diseases they can cause. I conducted a longitudinal species survey of snails and trematodes across six lakes in central Alberta over three summers. From the survey, we applied morphological and molecular genetic analyses to identify snail and trematode species. Overall, we uncovered an incredible diversity of trematodes, with 67 species and counting. Surprisingly, there were only five snail species needed to host them. From spatio-temporal analyses, we found no clear patterns for species composition in communities, though it does appear as if the ecoregion and the amount of nutrients in the water determining the trophic status may be playing a role. Furthermore, for some very abundant species, dissolved oxygen content in the water is an important predictor for their presence. All communities examined shared a trematode composition pattern of a few highly abundant and common trematode species, and many rare and inconsistent species. This information has important implications for the local public health issue of swimmer’s itch in Alberta. Swimmer’s itch is a re-emerging, neglected allergic condition caused by trematodes of the family Schistosomatidae. People are exposed to the larvae of schistosomes when swimming and recreating in natural water bodies. The larvae emerge from their snail first intermediate host and actively penetrate the skin of unsuspecting swimmers, causing a rash that can last up to two weeks. What these larvae are actually attempting to do is to infect a duck, their definitive host. These accidental exposures to humans have many downstream public health impacts, most being indirect effects as a result of discontinued use of lakes for recreation, due to the economic, cultural, and spiritual values associated with them. My doctoral research has laid the foundation for understanding the aspects of the swimmer’s itch issue, the biological side and the human perspective. From our species survey, we found seven schistosome species capable of causing swimmer’s itch, and all were rare in each community. This was a surprising result, given that our swimmer’s itch survey, a longitudinal survey of people who had experienced swimmer’s itch from across Canada, revealed many reports of swimmer’s itch every year, even from the lakes we had directly sampled snails from. In total, in Alberta there were 101 lakes that had reported swimmer’s itch over five years. One trend found among both surveys was the occurrence of peaks in trematode species diversity, snail infection prevalence, and swimmer’s itch occurrences during the months of July and August, which will be an interesting avenue for future research. Overall, my doctoral research has contributed to a broad understanding of swimmer’s itch transmission, as well as the spatio-temporal dynamics of trematode community assembly processes.

• Subjects / Keywords

  • Alberta
  • Digenea
  • Trematode
  • Diversity
  • Gastropod
  • Snail
  • Swimmer's itch
  • Cercarial dermatitis
  • cercariae
  • lake

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-xm78-5r91

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.