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Parasitology 1989The paper examines non-linear dynamical phenomena in host-parasite interactions by reference to a series of different problems ranging from the impact on transmission of... (Review)
Review
The paper examines non-linear dynamical phenomena in host-parasite interactions by reference to a series of different problems ranging from the impact on transmission of control measures based on vaccination and chemotherapy, to the effects of immunological responses targeted at different stages in a parasite's life-cycle. Throughout, simple mathematical models are employed to aid in interpretation. Analyses reveal that the influence of a defined control measure on the prevalence or intensity of infection, whether vaccination or drug treatment, is non-linearly related to the magnitude of control effort (as defined by the proportion of individuals vaccinated or treated with a drug). Consideration of the relative merits of gametocyte and sporozoite vaccines against malarial parasites suggests that very high leves of cohort immunization will be required to block transmission in endemic areas, with the former type of vaccine being more effective in reducing transmission for a defined level of coverage and the latter being better with respect to a reduction in morbidity. The inclusion of genetic elements in analyses of the transmission of helminth parasites reveals complex non-linear patterns of change in the abundance of different parasite genotypes under selection pressures imposed by either the host immunological defences or the application of chemotherapeutic agents. When resistance genes are present in parasite populations, the degree to which abundance can be suppressed by chemotherapy depends critically on the frequency and intensity of application, with intermediate values of the former being optimal. A more detailed consideration of the impact of immunological defences on parasite population growth within an individual host, by reference to the erythrocytic cycle of malaria, suggests that the effectiveness of a given immunological response is inversely related to the life-expectancy of the target stage in the parasite's developmental cycle.
Topics: Animals; Drug Resistance; Host-Parasite Interactions; Humans; Mathematics; Models, Biological; Parasites; Parasitic Diseases; Vaccines
PubMed: 2682486
DOI: 10.1017/s0031182000083426 -
Biology Letters Mar 2019Male-biased susceptibility to parasites is common in dioecious plants. However, why males have higher parasite loads than females is unclear. Unlike males, females must...
Male-biased susceptibility to parasites is common in dioecious plants. However, why males have higher parasite loads than females is unclear. Unlike males, females must subsidize post-fertilization costs of reproduction (e.g. seed and fruit development). As a result, females may have smaller pools of resources potentially available to parasites, thus leading to lower parasite loads. We tested this prediction in New Zealand's largest native moth ( Aenetus virescens: Lepidoptera), whose larvae parasitize Aristotelia serrata (Elaeocarpaceae), an endemic species of dioecious tree. We measured parasite loads in male and female trees, as well as annual seed set in females. We then derived a technique to equate the energetic cost of seed set in females to an equivalent number of parasitic larvae. Our results showed evidence for male-biased parasitism: male trees harboured more larval parasites than female trees. However, when parasite loads in males were compared with parasite loads in females, plus the energetic cost of seed production calculated as an equivalent number of parasitic larvae, differences in parasitism between the sexes disappeared. We conclude that male-biased parasitism in plants could arise from parasite-offspring (i.e. herbivore-seed) competition for female resources.
Topics: Animals; Female; Larva; Male; New Zealand; Parasites; Reproduction; Trees
PubMed: 30836880
DOI: 10.1098/rsbl.2018.0761 -
Tropical Medicine & International... Jun 2012To review methods for the statistical analysis of parasite and other skewed count data. (Review)
Review
OBJECTIVE
To review methods for the statistical analysis of parasite and other skewed count data.
METHODS
Statistical methods for skewed count data are described and compared, with reference to a 10-year period of Tropical Medicine and International Health (TMIH). Two parasitological datasets are used for illustration.
RESULTS
The review of TMIH found 90 articles, of which 89 used descriptive methods and 60 used inferential analysis. A lack of clarity is noted in identifying the measures of location, in particular the Williams and geometric means. The different measures are compared, emphasising the legitimacy of the arithmetic mean for the skewed data. In the published articles, the t test and related methods were often used on untransformed data, which is likely to be invalid. Several approaches to inferential analysis are described, emphasising (1) non-parametric methods, while noting that they are not simply comparisons of medians, and (2) generalised linear modelling, in particular with the negative binomial distribution. Additional methods, such as the bootstrap, with potential for greater use are described.
CONCLUSIONS
Clarity is recommended when describing transformations and measures of location. It is suggested that non-parametric methods and generalised linear models are likely to be sufficient for most analyses.
Topics: Animals; Humans; Linear Models; Parasite Load; Parasites; Parasitology; Research Design
PubMed: 22943299
DOI: 10.1111/j.1365-3156.2012.02987.x -
Parasitology Nov 2011Herein we review theoretical and methodological considerations important for finding and delimiting cryptic species of parasites (species that are difficult to recognize... (Review)
Review
Herein we review theoretical and methodological considerations important for finding and delimiting cryptic species of parasites (species that are difficult to recognize using traditional systematic methods). Applications of molecular data in empirical investigations of cryptic species are discussed from an historical perspective, and we evaluate advantages and disadvantages of approaches that have been used to date. Developments concerning the theory and practice of species delimitation are emphasized because theory is critical to interpretation of data. The advantages and disadvantages of different molecular methodologies, including the number and kind of loci, are discussed relative to tree-based approaches for detecting and delimiting cryptic species. We conclude by discussing some implications that cryptic species have for research programmes in parasitology, emphasizing that careful attention to the theory and operational practices involved in finding, delimiting, and describing new species (including cryptic species) is essential, not only for fully characterizing parasite biodiversity and broader aspects of comparative biology such as systematics, evolution, ecology and biogeography, but to applied research efforts that strive to improve development and understanding of epidemiology, diagnostics, control and potential eradication of parasitic diseases.
Topics: Animals; Biodiversity; Classification; Genetic Techniques; Helminthiasis, Animal; Helminths; Parasites; Parasitology; Species Specificity
PubMed: 21281559
DOI: 10.1017/S003118201000168X -
Parasite (Paris, France) Sep 2008Parasite requires an understanding of complex transmission systems where individual, population and environmental factors and their interactions can hardly been... (Review)
Review
Parasite requires an understanding of complex transmission systems where individual, population and environmental factors and their interactions can hardly been considered separately. Moreover, the importance of space and time in host population and parasite transmission processes is increasingly recognised. The present review illustrates how epidemiology and transmission ecology have evolved in a multidisciplinary framework to a systems approach that includes both spatial and temporal dimensions. Focusing on population processes, three significant challenges are discussed: (i) integration of landscape ecology concepts and modelling across time-space scales, (ii) development of molecular methods that permits easy parasite/host identification and process tracking (e.g. host and parasite movements), and (iii) integration of sociology methods to estimate zoonotic risk and exposure.
Topics: Animals; Demography; Ecosystem; Host-Parasite Interactions; Humans; Parasites; Parasitic Diseases; Parasitology; Risk Assessment; Sentinel Surveillance; Space-Time Clustering; Species Specificity
PubMed: 18814725
DOI: 10.1051/parasite/2008153469 -
The Veterinary Record Jul 2013
Review
Topics: Animals; Anniversaries and Special Events; Antiparasitic Agents; Host-Parasite Interactions; Humans; Life Cycle Stages; Parasites; Parasitic Diseases, Animal; Parasitology; Periodicals as Topic; Veterinary Medicine
PubMed: 23893587
DOI: 10.1136/vr.f4698 -
Parasitology 1994Behavioural patterns involved in avoiding, repelling, or removing parasites allow mammalian hosts to defend themselves from an array of parasites that threaten the... (Review)
Review
Behavioural patterns involved in avoiding, repelling, or removing parasites allow mammalian hosts to defend themselves from an array of parasites that threaten the host's fitness in the natural world. Some examples of behavioural defenses and the presumed target parasites are: grooming to remove ticks, grouping to reduce attack rate of biting flies, fly repelling movements to reduce parasitic flies, and selective grazing to reduce intake of faecal-borne parasites. These behavioural defenses are discussed with regard to effectiveness in controlling the target parasites. Parasites have sometimes evolved behavioural strategies of evading, penetrating or disabling these behavioural defenses. These parasite behavioural strategies, though less studied, are discussed. Also discussed is the possibility that host behavioural patterns that may defend against one parasite may be exploited by a different type of parasite to facilitate its own transmission. The interplay between host defensive strategies, the cost versus the effectiveness of such strategies, and a parasite's evasion or exploitation of such strategies, may be useful in understanding some aspects of host-parasite dynamics in nature.
Topics: Animals; Arthropod Vectors; Behavior, Animal; Female; Host-Parasite Interactions; Male; Mammals; Parasites
PubMed: 7854847
DOI: 10.1017/s0031182000085140 -
Parasitology 1994Host location by parasites can be achieved by either active or passive mechanisms. In spite of their significance, the efficacy of these methods has been little... (Review)
Review
Host location by parasites can be achieved by either active or passive mechanisms. In spite of their significance, the efficacy of these methods has been little researched. High fecundity in parasites is discussed in terms of the role it plays in dispersal and transmission. Some concepts developed by mainstream behavioural ecologists are outlined and their relevance to parasitology is indicated. 'Reproductive value' is recommended as an appropriate measure of the costs and benefits of behavioural cts. Although costs of reproduction have been rarely studied in parasites, they are likely to occur in cosexual insects, nematodes and crustaceans. Experiments using captive hosts and/or in vitro cultivation could help in the construction of realistic optimality models. We suggest that r- and K-selection theory could assist in the study of the evolution of parasite behaviour. We discuss how parasite populations are dispersed and controlled and consider the implications of overdispersion. We outline three sources of signals to which parasites may respond and suggest that understanding evolutionary mechanisms and community organisation of parasites and hosts requires evaluation of fundamental behavioural responses to environmental signals. The study of closely related groups of parasites and their hosts may advance our knowledge of the evolution of parasite life cycles and the evolutionary costs and benefits of behavioural acts.
Topics: Animals; Ecology; Host-Parasite Interactions; Parasites; Parasitic Diseases; Reproduction
PubMed: 7854850
DOI: 10.1017/s0031182000085061 -
Parassitologia Sep 1997The degree of biological diversity is often used as an indicator of the well-being of ecological systems. This approach can also be applied to analyse biodiversity in... (Review)
Review
The degree of biological diversity is often used as an indicator of the well-being of ecological systems. This approach can also be applied to analyse biodiversity in parasite communities. In particular, studies on parasite communities can be employed to detect a decline in biodiversity which characterizes habitats affected by pollution. Beside the most widely used diversity indices, such as the Shannon, Brillouin and inverse Simpson, that have been widely applied in different host-parasite systems, new approaches have been recently developed in order to overcome problems related to high dominance. Walther et al. (1995) proposed an asymptotic equation suitable for evaluating parasite species richness as a function of sampling effort. Such an equation was earlier proposed by Miller and Weigert (1989) to describe plant species diversity and to calculate true species richness as the ratio between the increase in species richness (a) and the parameter that set the species richness asymptote (b). True species richness has been shown to decline in parasite communities of mugilids collected in polluted areas. Biodiversity calculations can also be run in parallel with other biological studies for the description of environmental conditions. The completion of parasite life cycles requires complex biocoenotic interactions and is restricted by environmental constraints. Therefore another approach for monitoring the health of an ecosystem was by analysing the ratio between monoxenous and heteroxenous parasite species infecting model hosts. By this methodology it was possible to confirm pollution effect highlighted by other quantitative methods.
Topics: Animals; Ecosystem; Environmental Monitoring; Fish Diseases; Fishes; Parasites; Parasitic Diseases, Animal; Water Pollution
PubMed: 9802073
DOI: No ID Found -
Parasitology Dec 2012Phylogeography of parasites and microbes is a recent field. Phylogeographic studies have been performed mostly to test three major hypotheses that are not mutually... (Review)
Review
Phylogeography of parasites and microbes is a recent field. Phylogeographic studies have been performed mostly to test three major hypotheses that are not mutually exclusive on the origins and distributions of human parasites and microbes: (1) the "out of Africa" pattern where parasites are supposed to have followed the dispersal and expansion of modern humans in and out of Africa, (2) the "domestication" pattern where parasites were captured in the domestication centres and dispersed through them and (3) the "globalization" pattern, in relation to historical and more recent trade routes. With some exceptions, such studies of human protozoans, helminths and ectoparasites are quite limited. The conclusion emphasizes the need to acquire more phylogeographic data in non-Occidental countries, and particularly in Asia where all the animal domestications took place.
Topics: Animals; Biological Evolution; Host-Parasite Interactions; Humans; Parasites; Parasitic Diseases; Parasitology; Phylogeography
PubMed: 22717079
DOI: 10.1017/S0031182012000662