Gerald W. Esch

Patterns in helminth communities in freshwater fish in Great Britain: alternative strategies for colonization

Examples of the apparently stochastic nature of freshwater fish helminth communities illustrating the erratic and unpredictable occurrence and distribution of many species are provided for six species of fish from several localities throughout Britain. By focussing on parasite colonization strategies two categories of helminths are recognized: autogenic species which mature in fish and allogenic species which mature in vertebrates other than fish and have a greater colonization potential and ability. Three groups of fish are distinguished: salmonids, in which helminth communities are generally dominated by autogenic species which are also responsible for most of the similarity within and between localities; cyprinids, in which they are dominated by allogenic species which are also responsible for most of the similarity within and between localities; and anguillids, whose helminth communities exhibit intermediate features with neither category consistently dominating nor providing a clear pattern of similarity. Recognition and appreciation of the different colonization strategies of autogenic and allogenic helminths in respect of host vagility and ability to cross land or sea barriers and break down habitat isolation, and their period of residence in a locality, whether transient or permanent, provides an understanding of, and explanation for, the observed patchy spatial distribution of many helminths. Comparison with other parts of the world indicates that colonization is a major determinant of helminth community structure.

An Analysis of the Relationship Between Stress and Parasitism

The impact of stress upon the dynamics of host and parasite populations is varied. It may be expressed physiologically or behaviorally in either the host or the parasite. The outcome of stress may be an increase or a decrease in natality and mortality which may then result in significant changes in the densities of the involved popula- tions. At the ecosystem level, stress may be manifested either directly or indirectly on individuals or populations, but the outcome is change in natality or mortality and, hence, in the density of the affected species. The varied response to stressor input at the individual, population and ecosystem levels is dictated by the capacity for adaptability present at each level; the response may be modified, however, by the unique com- bination of environmental characteristics at the time of stressor input.

Parasites in Human Tissues

Since there are myriad books in the field of parasitology and tropical medicine, the question one is likely to ask when first confronted with the title of this book is whether it is yet another parasitology text. Parasites in Human Tissues is neither a general parasitology text nor a tropical medicine text. For example, in the malaria selection the authors describe the malarial parasite within vessels and in tissues such as the liver. If one is in need of aid in the identification of the blood stages of the various malarial parasites, one should seek out standard parasitology texts or atlases. Similarly, this volume is not a reference for the morphology of intestinal protozoa or helminths. There is a companion Atlas of Parasitology that can be used for such purposes. Parasites in Human Tissues, however, is a superb reference text for the histological diagnosis of parasites. The book is divided into the familiar, albeit arbitrary, divisions that have become part of any parasitology text, namely, protozoa, nematodes, trematodes, and arthropods; in addition there is a valuable section on artifacts. Series of helpful colorful charts in the beginning of the book assist the reader in understanding both the usual and the unusual locations of parasites within host tissues. For each parasite, there is a short summary of the biology and life

Microbiology and Microbial Infections

Microbiology and Microbial Infections , Microbiology and Microbial Infections , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Impact of ecological succession on the parasite fauna in centrarchids from oligotrophic and eutrophic ecosystems.

Approximately 30 species of larval and adult parasites were collected from 549 centrarchid fish and 7718 gastropod molluscs from an oligotrophic and two eutrophic lakes in southwestern Michigan. The distribution pattern indicates that centrarchids from the oligotrophic lake harbor a wide range of species of adult parasites and a comparatively smaller number of larval forms, many of which complete their life cycles in predatory fish. On the other hand, bass and sunfish from the two eutrophic lakes harbor a proportionately larger number of larval parasites, most of which culminate their life cycles in fish-eating birds and mammals. A trophic hypothesis, based on the nature of predatorprey relationships in each of the two types of ecosystem, is proposed to explain the distribution patterns of parasites.

A perspective on the ecology of trematode communities in snails

This paper presents a perspective on the ecology of trematodes in snail hosts based on recent evidence. Because flukes use snails almost obligatorily as first intermediate hosts, we highlight the role of gastropods as keystone species for trematodes and their communities. After reviewing recent developments in the transmission of trematodes to and from snails, we discuss trematode communities within individual snails (infracommunities) and in snail populations (component communities). Results garnered using various protocols at the infracommunity level are reviewed. The few data available, all from marine systems, indicate that low colonization rates characterize infracommunities, suggesting that trematode infracommunities tend to be isolationist in character rather than interactive. The variety of trematode species present in a component community seems to be determined by spatial overlap of definitive hosts. Relative abundance of species in a component community shows little dependence on negative interspecific interactions at the level of the infracommunity. Temporal aspects of trematode communities are related to the life history of the host snail. The component communities of long-lived snails (mostly marine) integrate many infection episodes whereas shorter-lived snails (mostly freshwater) acquire new component communities each time host cohorts turnover.

Guild structure of larval trematodes in the snail Helisoma anceps : patterns and processes at the individual host level

Factors that influenced the infracommunity structure of trematodes parasitizing the pulmonate snail Helisoma anceps were studied over a 15-mo period; the guild included 8 species of parasites. Infracommunities were depauperate, with double patent infections observed in only 7 of 1,485 infected snails; a total of 4,899 was examined. Halipegus occidualis-Haematoloechus longiplexus was the most common dual infection. Both species share the same definitive host and, in both cases, eggs are the infective stage for the snail. Switches and losses of infections in individual snails were observed, suggesting the occurrence of dynamic interactions within the guild. A dominance hierarchy was constructed based on field observations and experimental infections. Echinostomatids were dominant; species without rediae in their life cycles were subordinates. Halipegus occidualis (which has rediae) was intermediate in dominance. Spatial and temporal heterogeneity in the distribution and abundance of trematode infective stages indicate that not all the snails have the same probability of becoming infected. Habitat structure, behavior of the definitive host, the nature of the infective stages, and snail population dynamics (mortality, recruitment, and size structure) generated spatial and temporal heterogeneity in this system. As a consequence, predictions of the probabilities of interspecific interactions based on an analysis of observed and expected frequencies of multiple infections could be inappropriate unless the potential sources of heterogeneity are considered.

Patterns and processes in helminth parasite communities: an overview

The structure of helminth communities, their dynamic components and processes and their range of diversities, have long held fascination for parasitologists. Perhaps the earliest body of work in this area was generated by the great Russian academician, V. A. Dogiel and his colleagues in the 1930s (Dogiel, 1964). While it is generally agreed that Crofton (1971a, b) was largely responsible for introducing a quantitative approach to the study of helminth population dynamics, most agree that Holmes (1961, 1962) initiated a quantitative approach to the study of helminth community dynamics. Since these bench-mark publications, significant advances have been made in each area, both empirically and conceptually. Indeed, some of the terminology and ideas which will be highlighted throughout this book were not in the literature at the time the idea for this publication was conceived a little over two years ago.

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.

The effects of spatial and temporal heterogeneity as structuring forces for parasite communities in Helisoma anceps and Physa gyrina

-A total of 1231 Physa gyrina and 1532 Helisoma anceps were collected over a 12-mo period from Charlies Pond, in Stokes County, North Carolina. Similarity in the infraand component parasite communities in Helisoma anceps and Physa gyrina provided an opportunity to compare the effects of various life history traits on infection by larval trematodes in a number of different microhabitats. In order to assess the effects of microhabitat partitioning on the infection status of the two snail species, collections were made twice per month. Site location, water depth, snail depth at capture, distance from shore, type of substratum, infection status, and host size were recorded for each snail. Multivariate statistics were used to assess which variables determined a snails infection status. Data analysis indicated that certain of the microhabitat variables are better predictors of a snails infection status than others. Comparing uninfected snails to those infected with a specific parasite species, there was much disparity with regard to which microhabitat characteristic varied significantly. Manipulation of infracommunity structure, by excluding certain parasites, allowed examination of the influence of temporal heterogeneity as compared to interspecific trematode interactions in structuring the infraand component communities. Snails were maintained in cages in the field. Enclosures were positioned a few centimeters above the substratum to prevent infection of the snails via egg ingestion and effectively prevented the more prevalent parasite species (Halipegus occidualis in H. anceps and Halipegus eccentricus in P gyrina) from infecting the snails. Statistical analyses indicate that preventing snails from ingesting eggs of some parasites had no affect on the recruitment of other parasites. Parasite prevalences in H. anceps and P gyrina were not different in caged snails compared with those collected from the substrata of the pond.