The Transmission of Digenetic Trematodes: Style, Elegance, Complexity

Abstract

Traditionally, the field of parasitology has dealt with eukaryotic animals, to the exclusion of viruses, bacteria, fungi, etc., which is the way it will be approached here. The focus of the present paper will be on certain ecological aspects of the life cycles and life-history strategies employed by the Digenea, a diverse group of platyhelminths that includes some 25,000 species. More specifically, the review will consider the nature of host/parasite interactions within molluscan intermediate hosts and the manner in which these interactions, or lack thereof, function in structuring trematode infracommunities within these molluscan intermediate hosts. Literature in this area suggests that predation/competition may be a significant structuring force for infracommunities in certain marine prosobranchs, but not others, and that temporal/spatial factors may be involved as structuring mechanisms in at least some freshwater pulmonates.

Helminth communities in the burrowing toad, Rhinella fernandezae, from Northeastern Argentina

“…Helminth communities were classified at the infracommunity level (i.e., all helminth infrapopulations within a single burrowing toad) and component community level (i.e., all helminth infracommunities within a population of burrowing toad) (Esch et al 2002). Spearman's rank test (rs) was used to assess the relationship between the host body size and infracommunity descriptors and calculate possible correlations between the host body size and parasite abundances.…”

“…Specifically, extensive examination of many additional host species is needed before the helminth diversity of Argentinean amphibians can be adequately known, as well as for making robust predictions about parasite specificity (generalist vs. specialist), importance of a species within the community, e.g., dominant helminth species, and characteristics of the helminth communities (interactive vs. isolationist). Likewise, the spatial and temporal variations of larval parasites and the colonization abilities of parasites which could also influence the parasite assemblage in the definitive host (Esch et al 2002). So far, the present study is the first one investigating the ecological aspects of all groups of parasitic helminths (i.e., platyhelminths, nematodes and acanthocephalan) in terrestrial amphibians from Argentina, at the component and infracommunity levels.…”

Factors affecting trematode infection rates in freshwater mussels

“…In contrast to monogeneans, digenean trematodes evolved complex life cycles which typically involve larvae that reproduce asexually in one or more intermediate invertebrate or vertebrate hosts and an adult stage that reproduces sexually in a definite vertebrate host. The asexual reproduction of larvae was postulated to play a major role in the origin of the spectacular diversity of digenean trematodes (Cribb et al, 2001Esch et al, 2002;Poulin & Cribb, 2002).…”

Ecophysiology meets conservation: understanding the role of disease in amphibian population declines

“…They hypothesized that a decrease in T-lymphocyte production would result in decreased signalling of B-lymphocytes, which would reduce antibody production and, in turn, compromise immunity during periods of lower temperature. Thus, it is likely that prevalence of ranaviruses in amphibian populations is influenced by water temperature [79] [80]. Owing to the biphasic life cycle of amphibians, which generally includes an aquatic larval stage followed by a more terrestrial adult stage, they function as both second intermediate or definitive hosts to hundreds of different trematode species [22,81 -83].…”