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Journal ArticleDOI

Multiparasite communities in animals and humans: frequency, structure and pathogenic significance.

01 Mar 1998-International Journal for Parasitology (Pergamon)-Vol. 28, Iss: 3, pp 377-393
TL;DR: This review summarises aspects of current knowledge on the frequency of multiparasite infections, the factors which influence them, and their pathogenic significance.
About: This article is published in International Journal for Parasitology.The article was published on 1998-03-01. It has received 419 citations till now. The article focuses on the topics: Microparasite.
Citations
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Journal ArticleDOI
TL;DR: Parasites are affected when they themselves, or other organisms, interact with the immune response and, in particular, the cytokine network and the importance of such interactions is discussed in relation to clinical disease and the development and use of vaccines.
Abstract: Concomitant infections are common in nature and often involve parasites. A number of examples of the interactions between protozoa and viruses, protozoa and bacteria, protozoa and other protozoa, protozoa and helminths, helminths and viruses, helminths and bacteria, and helminths and other helminths are described. In mixed infections the burden of one or both the infectious agents may be increased, one or both may be suppressed or one may be increased and the other suppressed. It is now possible to explain many of these interactions in terms of the effects parasites have on the immune system, particularly parasite-induced immunodepression, and the effects of cytokines controlling polarization to the Th1 or Th2 arms of the immune response. In addition, parasites may be affected, directly or indirectly, by cytokines and other immune effector molecules and parasites may themselves produce factors that affect the cells of the immune system. Parasites are, therefore, affected when they themselves, or other organisms, interact with the immune response and, in particular, the cytokine network. The importance of such interactions is discussed in relation to clinical disease and the development and use of vaccines.

632 citations


Cites background from "Multiparasite communities in animal..."

  • ...…that have been investigated experimentally, there is some degree of interaction, sometimes very dramatic (Christensen et al. 1987; Chieffi, 1992; Petney & Andrews, 1998; see Behnke et al. this supplement) Some of these interactions are now beginning to be subjected to the kind of analysis…...

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  • ...There are many examples of concomitant infections in humans and animals (see for example Christensen et al. 1987; Ashford, 1991; Petney & Andrews, 1998; Viera et al. 1998)....

    [...]

Journal ArticleDOI
TL;DR: How techniques from community ecology can be used to restructure the approaches used to study parasite communities are highlighted and insights offered are discussed that will be crucial for predicting the impact on wildlife and human health of disease control measures, climate change or novel parasite species introductions.
Abstract: In natural systems, individuals are often co-infected by many species of parasites. However, the significance of interactions between species and the processes that shape within-host parasite communities remain unclear. Studies of parasite community ecology are often descriptive, focusing on patterns of parasite abundance across host populations rather than on the mechanisms that underlie interactions within a host. These within-host interactions are crucial for determining the fitness and transmissibility of co-infecting parasite species. Here, we highlight how techniques from community ecology can be used to restructure the approaches used to study parasite communities. We discuss insights offered by this mechanistic approach that will be crucial for predicting the impact on wildlife and human health of disease control measures, climate change or novel parasite species introductions.

522 citations

Journal ArticleDOI
TL;DR: Parasitic plants can alter the physical environment around them--including soil water and nutrients, atmospheric CO2 and temperature--and so may also be considered as ecosystem engineers, which can have further consequences in altering the resource supply to and behaviour of other organisms within parasitic plant communities.
Abstract: Parasitic plants have profound effects on the ecosystems in which they occur. They are represented by some 4000 species and can be found in most major biomes. They acquire some or all of their water, carbon and nutrients via the vascular tissue of the host's roots or shoots. Parasitism has major impacts on host growth, allometry and reproduction, which lead to changes in competitive balances between host and nonhost species and therefore affect community structure, vegetation zonation and population dynamics. Impacts on hosts may further affect herbivores, pollinators and seed vectors, and the behaviour and diversity of these is often closely linked to the presence and abundance of parasitic plants. Parasitic plants can therefore be considered as keystone species. Community impacts are mediated by the host range of the parasite (the diversity of species that can potentially act as hosts) and by their preference and selection of particular host species. Parasitic plants can also alter the physical environment around them--including soil water and nutrients, atmospheric CO2 and temperature--and so may also be considered as ecosystem engineers. Such impacts can have further consequences in altering the resource supply to and behaviour of other organisms within parasitic plant communities.

430 citations

Journal ArticleDOI
TL;DR: The authors' ecological understanding of wildlife infectious diseases from the individual host to the ecosystem scale is reviewed, highlighting where conceptual thinking lacks verification, discussing difficulties and challenges, and offering potential future research directions.
Abstract: 1. We review our ecological understanding of wildlife infectious diseases from the individual host to the ecosystem scale, highlighting where conceptual thinking lacks verification, discussing difficulties and challenges, and offering potential future research directions. 2. New molecular approaches hold potential to increase our understanding of parasite interactions within hosts. Also, advances in our knowledge of immune systems makes immunological parameters viable measures of parasite exposure, and useful tools for improving our understanding of causal mechanisms. 3. Studies of transmission dynamics have revealed the importance of heterogeneity in host behaviour and physiology, and of contact processes operating at different spatial and temporal scales. An important future challenge is to determine the key transmission mechanisms maintaining the persistence of different types of diseases in the wild. 4. Regulation of host populations is too complex to consider parasite effects in isolation from other factors. One solution is to seek a unified understanding of the conditions under which (and the ecological rules determining when) population scale impacts of parasites can occur. 5. Good evidence now shows that both direct effects of parasites, and trait mediated indirect effects, frequently mediate the success of invasive species and their impacts on recipient communities. A wider exploration of these effects is now needed. 6. At the ecosystem scale, research is needed to characterize the circumstances and conditions under which both fluxes in parasite biomass, and trait mediated effects, are significant in ecosystem processes, and to demonstrate that parasites do indeed increase 'ecosystem health'. 7. There is a general need for more empirical testing of predictions and subsequent development of theory in the classic research cycle. Experimental field studies, meta-analyses, the collection and analysis of long-term data sets, and data constrained modelling, will all be key to advancing our understanding. 8. Finally, we are only now beginning to understand the importance of cross-scale interactions associated with parasitism. Such interactions may offer key insights into bigger picture questions such as when and how different regulatory factors are important, when disease can cause species extinctions, and what characteristics are indicative of functionally resilient ecosystems.

393 citations

Book ChapterDOI
TL;DR: This chapter reviews recent advances in the understanding in the biology, immunology, epidemiology, public health significance and control of hookworm, and to look forward to the study of this important parasite in the 21st century.
Abstract: The scientific study of human hookworm infection began at the dawn of the twentieth century. In recent years, there have been dramatic improvements in our understanding of many aspects of this globally widespread parasite. This chapter reviews recent advances in our understanding in the biology, immunology, epidemiology, public health significance and control of hookworm, and to look forward to the study of this important parasite in the 21st century. Advances in molecular biology has lead to the identification of a variety of new molecules from hookworms, which have importance either in the molecular pathogenesis of hookworm infection or in the host-parasite relationship; some are also promising vaccine targets. At present, relatively little is known about the immune responses to hookworm infection, although it has recently been speculated that hookworm and other helminths may modulate specific immune responses to other pathogens and vaccines. Our epidemiological understanding of hookworm has improved through the development of mathematical models of transmission dynamics, which coupled with decades of field research across multiple epidemiological settings, have shown that certain population characteristics can now be recognised as common to the epidemiology, population biology and control of hookworm and other helminth species. Recent recognition of the subtle, but significant, impact of hookworm on health and education, together with the simplicity, safety, low cost and efficacy of chemotherapy has spurred international efforts to control the morbidity due to infection. Large-scale treatment programmes are currently underway, ideally supported by health education and integrated with the provision of improved water and sanitation. There are also on-going efforts to develop novel anthelmintic drugs and anti-hookworm vaccines.

389 citations

References
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Book
11 Jul 1991
TL;DR: This book discusses the biology of host-microparasite associations, dynamics of acquired immunity heterogeneity within the human community indirectly transmitted helminths, and the ecology and genetics of hosts and parasites.
Abstract: Part 1 Microparasites: biology of host-microparasite associations the basic model - statics static aspects of eradication and control the basic model - dynamics dynamic aspects of eradication and control beyond the basic model - empirical evidence of inhomogeneous mixing age-related transmission rates genetic heterogeneity social heterogeneity and sexually transmitted diseases spatial and other kinds of heterogeneity endemic infections in developing countries indirectly transmitted microparasites. Part 2 Macroparasites: biology of host-macroparasite associations the basic model - statics the basic model - dynamics acquired immunity heterogeneity within the human community indirectly transmitted helminths experimental epidemiology parasites, genetic variability, and drug resistance the ecology and genetics of host-parasite associations.

7,675 citations

Journal ArticleDOI
02 Aug 1979-Nature
TL;DR: Consideration is given to the relation between the ecology and evolution of the transmission processes and the overall dynamics, and to the mechanisms that can produce cyclic patterns, or multiple stable states, in the levels of infection in the host population.
Abstract: If the host population is taken to be a dynamic variable (rather than constant, as conventionally assumed), a wider understanding of the population biology of infectious diseases emerges. In this first part of a two-part article, mathematical models are developed, shown to fit data from laboratory experiments, and used to explore the evolutionary relations among transmission parameters. In the second part of the article, to be published in next week's issue, the models are extended to include indirectly transmitted infections, and the general implications for infectious diseases are considered.

2,652 citations

Journal ArticleDOI
TL;DR: Competition was found in 90% of the studies and 76% of their species, indicating its pervasive importance in ecological systems, and the Hairston-Slobodkin-Smith hypothesis concerning variation in the importance of competition between trophic levels was strongly supported.
Abstract: The study of interspecific competition has long been one of ecology's most fashionable pursuits. Stimulated in part by a simple theory (Lotka 1932; Volterra 1926; Gause 1934; Hutchinson 1959; MacArthur and Levins 1967), ecologists gathered numerous data on the apparent ways species competitively coexist or exclude one another (reviews in Schoener 1974b, 1983). As is typical in science, most of the early data were observational, and the few experimental studies were mostly performed in the laboratory rather than in the field. Though never lacking its doubters, the belief in the natural importance of interspecific competition is now being severely questioned (review in Schoener 1982). Many of the putatively supportive observations have been challenged as being statistically indistinguishable from random contrivance. Most such attacks have been rebutted, but not without some modification of original conclusions (e.g., papers in Strong et al. 1983). New observations have been gathered for certain systems, suggesting a lack of competitively caused patterns and catalyzing the variable environment view of Wiens (1977) in which competition is seen as a temporally sporadic, often impotent, interaction. Other critics have charged that the lack of experimental field evidence for competition would preclude its acceptance regardless of the quality of observational data. Indeed, results of some of the earlier field experiments are in part responsible for competition's presently beleaguered state. Connell (1975), after reviewing the field experiments known to him through 1973, concluded that predation, rather than competition, appears to be the predominant ecological interaction and should be given "conceptual priority." Shortly afterward, Schroder and Rosenzweig (1975) showed experimentally that two species of desert rodents overlapping substantially in habitat did not appear to affect one another's abundances. This result was interpreted as contradicting a crucial assumption of competition theory, almost its linchpin: the greater the resource overlap between species, the greater the competition coefficient, a measure of the intensity of interspecific competition (relative to intraspecific competition; MacArthur and Levins 1967; review in Roughgarden 1979).

2,256 citations

Journal ArticleDOI
TL;DR: The present survey illustrates how difficult it is to produce a clear and unambiguous demonstration of interspecific competition.
Abstract: In a strictly defined sample of competition studies using controlled field experiments, covering 215 species and 527 experiments, competition was found in most of the studies, in somewhat more than half of the species, and in about two-fifths of the experiments. In most of these experiments interspecific competition was not distinguished from intraspecific competition. In the few studies in which the two were separated, interspecific competition was the stronger form in about onesixth of all experiments done. When competition was demonstrated, intraspecific competition was as strong or stronger than interspecific in three-quarters of the experiments. Some evidence from this literature survey suggests that negative results may be underrepresented, so that the absolute values of these figures may be too high. Since this bias should apply also to studies of all taxa, habitats, or other interactions it should not greatly affect estimates of the relative prevalence of competition. Since these estimates come fr...

1,895 citations

Journal ArticleDOI
TL;DR: Genus- and species-specific sequences are present within the small subunit ribosomal RNA genes of the four human malaria parasites that have proven to be more sensitive and accurate than by routine diagnostic microscopy.

836 citations