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Definitive Hosts (definitive + hosts)
Selected AbstractsSpatial variation in population density across the geographical range in helminth parasites of yellow perch Perca flavescensECOGRAPHY, Issue 5 2007Robert Poulin The abundance of a species is not constant across its geographical range; it has often been assumed to decrease from the centre of a species' range toward its margins. The central assumption of this "favourable centre" model is tested for the first time with parasites, using different species of helminth parasites exploiting fish as definitive hosts. Data on prevalence (percentage of hosts that are infected) and abundance (mean no. parasites per host) were compiled for 8 helminth species occurring in 23 populations of yellow perch Perca flavescens, from continental North America. For each parasite species, correlations were computed between latitude and both local prevalence and abundance values. In addition, the relationships between the relative prevalence or abundance in one locality and the distance between that locality and the one where the maximum value was reported, were assessed separately for each species to determine whether abundance tends to decrease away from the presumed centre of the range, where it peaks. For both the cestode Proteocephalus pearsei and the acanthocephalan Leptorhynchoides thecatus, there was a positive relationship between prevalence or abundance and the latitude of the sampled population. There was also a significant negative relationship between relative prevalence and the distance from the locality showing the maximum value in P. pearsei, but no such pattern was observed for the other 7 parasite species. Since this single significant decrease in prevalence with increasing distance from the peak value may be confounded by a latitudinal gradient, it appears that the distribution of abundance in parasites of perch does not follow the favourable centre model. This means that the environmental variables affecting the density of parasites (host availability, abiotic conditions) do not show pronounced spatial autocorrelation, with nearby sites not necessarily providing more similar conditions for the growth of parasite populations than distant sites. [source] Helminth parasitism of Galaxias maculatus (Jenyns 1842) in southwestern AustraliaECOLOGY OF FRESHWATER FISH, Issue 4 2006A. Chapman Abstract , One cestode, Ligula sp. [possibly Ligula intestinalis (L.)], one trematode, Diplostomum sp., and two nematode parasitic worms, Eustrongylides sp. [possibly Eustrongylides gadopsis (Royal Society of South Australia, 64, 340)] and Contracaecum sp. are reported from Galaxias maculatus inhabiting a permanent freshwater lake and two intermittently flowing, saline rivers in southwestern Australia. Worms infecting fish are all larval; the definitive hosts are piscivorous waterfowl. Ligula sp. infected 12% of fish in the lake. Effects of infection include reduced lifespan, significant weight reduction of gonads of males and females and body weight of females. Infection reduces the proportion of males that attain spawning gonad stage more severely than it does in females. The prevalence and intensity of Ligula sp. infection were much less in the rivers. The infection of Pseudogobius olorum (Sauvage 1880) by this cestode is reported for the first time in Western Australia. Trematodes were much more benign in their effect on G. maculatus. [source] An Analysis of Possible Mechanisms of Unexpected Death Occurring in Hydatid Disease (Echinococcosis)JOURNAL OF FORENSIC SCIENCES, Issue 4 2009Roger W. Byard M.B.B.S. Abstract:, Most cases of hydatid disease in human populations are due to Echinococcus granulosus. The hydatid life cycle involves passage between definitive hosts such as dogs and intermediate hosts such as sheep. Humans become accidental intermediate hosts following ingestion of food or water contaminated with eggs or by contact with infected dogs. Although hydatid disease may remain asymptomatic, occasional cases of sudden and unexpected death present to autopsy. Causes of rapid clinical decline involve a wide range of mechanisms including anaphylaxis (with or without cyst rupture), cardiac outflow obstruction or conduction tract disturbance, pulmonary and cerebral embolism, pericarditis, cardiac tamponade, myocardial ischemia, pulmonary hypertension, peritonitis, hollow organ perforation, intracerebral mass effect, obstructive hydrocephalus, seizures, cerebral ischemia/infarction, and pregnancy complications. The autopsy assessment of cases therefore requires careful examination of all organ systems for characteristic cystic lesions, as multiorgan involvement is common, with integration of findings so that possible mechanisms of death can be determined. Measurement of serum tryptase and specific IgE levels should be undertaken for possible anaphylaxis. [source] Rising burden of immature sheep ticks (Ixodes ricinus) on red grouse (Lagopus lagopus scoticus) chicks in the Scottish uplandsMEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2004A. D. Kirby Abstract., The sheep tick Ixodes ricinus (L.) (Acari: Ixodidae) is an ectoparasite of major economic and pathogenic importance in Scotland. Its distribution in the Scottish uplands is assumed to be governed by the abundance and distribution of its definitive hosts (deer and sheep) and climatic variables such as temperature and rainfall. As the numbers of its major host in Scotland, red deer, have increased dramatically and climatic conditions have become more favourable, the level of parasitism could have been expected to rise. We use data gathered from tick counts on over 4000 red grouse chicks Lagopus lagopus scoticus Latham (Galliformes: Tetraonidae) in various experiments over the past 19 years to ascertain whether the intensity and prevalence of parasitism has been increasing. From 1985 to 2003 the average tick burden of a parasitized red grouse chick has grown from 2.60 ± 1.12 ticks per chick to 12.71 ± 1.44. Over this period the percentage of chicks of a given brood parasitized has also increased from 4 ± 2% to 92 ± 3%. The possible implications of this increase in parasitism for red grouse production are discussed. [source] Contrasting mtDNA diversity and population structure in a direct-developing marine gastropod and its trematode parasitesMOLECULAR ECOLOGY, Issue 22 2009DEVON B. KEENEY Abstract The comparative genetic structure of hosts and their parasites has important implications for their coevolution, but has been investigated in relatively few systems. In this study, we analysed the genetic structure and diversity of the New Zealand intertidal snail Zeacumantus subcarinatus (n = 330) and two of its trematode parasites, Maritrema novaezealandensis (n = 269) and Philophthalmus sp. (n = 246), using cytochrome c oxidase subunit I gene (COI) sequences. Snails and trematodes were examined from 11 collection sites representing three regions on the South Island of New Zealand. Zeacumantus subcarinatus displayed low genetic diversity per geographic locality, strong genetic structure following an isolation by distance pattern, and low migration rates at the scale of the study. In contrast, M. novaezealandensis possessed high genetic diversity, genetic homogeneity among collection sites and high migration rates. Genetic diversity and migration rates were typically lower for Philophthalmus sp. compared to M. novaezealandensis and it displayed weak to moderate genetic structure. The observed patterns likely result from the limited dispersal ability of the direct developing snail and the utilization of bird definitive hosts by the trematodes. In addition, snails may occasionally experience long-distance dispersal. Discrepancies between trematode species may result from differences in their effective population sizes and/or life history traits. [source] Protecting babies: vaccine strategies to prevent foetopathy in Neospora caninum -infected cattlePARASITE IMMUNOLOGY, Issue 3 2006Review Article SUMMARY Neospora caninum is an apicomplexan protozoan parasite that is a significant infectious abortifacient agent in cattle. Despite the fact that it is a member of a well described taxonomic group, it is a relatively newly discovered parasite and its biology is not yet fully understood. Cattle become infected either congenitally via transplacental transmission or post-natally by ingesting oocysts derived from the definitive host; dogs and coyotes are the only definitive hosts that have been described to date. It is not known which of these two forms of transmission occurs most frequently and which is the most likely to result in abortion; there are no drugs available to treat infected cattle, so current control strategies rely on prevention of infection by management methods and strict hygiene; an effective vaccine would be a great advantage in its control. Neospora caninum is an economically important veterinary pathogen, but we can also draw analogies between its foetopathic effects and those of human pathogens such as Toxoplasma gondii, Chlamydophila abortus and Plasmodium falciparum. Understanding the immune response and the materno,foetal relationship in N. caninum -infected cattle may help us to design vaccination strategies, not only for neosporosis but also for other foetopathic agents. [source] | ||||||||||