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      Helminth communities from two urban rat populations in Kuala Lumpur, Malaysia

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          Abstract

          Background

          The prevalence of parasitic infections among commensal animals such as black and brown rats in many tropical countries is high and in comparison with studies on rodents in temperate climates, little is known about the community structure of their parasites. Rodent borne parasites pose threats to human health since people living in close proximity to rodent populations can be exposed to infection.

          Methods

          The helminth community structures of two urban rat populations in Kuala Lumpur, Malaysia were investigated. The rats were from two contrasting sites in the city caught over a period of 21 months in 2000-2002.

          Results

          Eleven species of helminth parasites comprising seven nematodes ( Heterakis spumosum, Mastophorus muris, Nippostrongylus brasiliensis, Syphacia muris, Pterygodermatites tani/whartoni, Gongylonema neoplasticum, Angiostrongylus malaysiensis ), three cestodes ( Hymenolepis ( Rodentolepis) nana, H. diminuta and Taenia taeniaeformis) and one acanthocephalan ( Moniliformis moniliformis) were recovered from 346 Rattus rattus and 104 R. norvegicus from two urban sites, Bangsar and Chow Kit, during 2000-2002. Rattus rattus harboured over 60% of all helminths compared with R. norvegicus, although both host species played a dominant role in the different sites with, for example R. norvegicus at Bangsar and R. rattus at Chow Kit accounting for most of the nematodes. Overall 80% of rats carried at least one species of helminth, with the highest prevalences being shown by H. diminuta (35%), H. spumosum (29.8%) and H. nana (28.4%). Nevertheless, there were marked differences in prevalence rates between sites and hosts. The influence of extrinsic (year, season and site) and intrinsic (species, sex and age) factors affecting infracommunity structure (abundance and prevalence of infection) and measures of component community structure were analyzed.

          Conclusions

          Since at least two species of rat borne helminths in Kuala Lumpur have the potential to infect humans, and these showed high prevalences in the rats, the assessment and regular monitoring of infections carried by wild rodents have important roles to play in public health.

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          Most cited references52

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          The interaction of parasites and resources cause crashes in a wild mouse population.

          1. Populations of white-footed mice Peromyscus leucopus and deer mice Peromyscus maniculatus increase dramatically in response to food availability from oak acorn masts. These populations subsequently decline following this resource pulse, but these crashes cannot be explained solely by resource depletion, as food resources are still available as population crashes begin. 2. We hypothesized that intestinal parasites contribute to these post-mast crashes; Peromyscus are infected by many intestinal parasites that are often transmitted by density-dependent contact and can cause harm to their hosts. To test our hypothesis, we conducted a factorial experiment in natural populations by supplementing food to mimic a mast and by removal of intestinal nematodes with the drug, ivermectin. 3. Both food supplementation and the removal of intestinal nematodes lessened the rate and magnitude of the seasonal population declines as compared with control populations. However, the combination of food supplementation and removal of intestinal nematodes prevented seasonal population crashes entirely. 4. We also showed a direct effect on the condition of individuals. Faecal corticosterone levels, an indicator of the stress response, were significantly reduced in populations receiving both food supplementation and removal of intestinal nematodes. This effect was observed in autumn, before the overwinter crash observed in control populations, which may indicate that stress caused by the combination of food limitation and parasite infection is a physiological signal that predicts low winter survival and reproduction. 5. This study is one of the few to demonstrate that the interaction between resource availability and infectious disease is important for shaping host population dynamics and emphasizes that multiple factors may drive oscillations in wild animal populations.
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            Comparative performance of species richness estimation methods.

            In most real-world contexts the sampling effort needed to attain an accurate estimate of total species richness is excessive. Therefore, methods to estimate total species richness from incomplete collections need to be developed and tested. Using real and computer-simulated parasite data sets, the performances of 9 species richness estimation methods were compared. For all data sets, each estimation method was used to calculate the projected species richness at increasing levels of sampling effort. The performance of each method was evaluated by calculating the bias and precision of its estimates against the known total species richness. Performance was evaluated with increasing sampling effort and across different model communities. For the real data sets, the Chao2 and first-order jackknife estimators performed best. For the simulated data sets, the first-order jackknife estimator performed best at low sampling effort but, with increasing sampling effort, the bootstrap estimator outperformed all other estimators. Estimator performance increased with increasing species richness, aggregation level of individuals among samples and overall population size. Overall, the Chao2 and the first-order jackknife estimation methods performed best and should be used to control for the confounding effects of sampling effort in studies of parasite species richness. Potential uses of and practical problems with species richness estimation methods are discussed.
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              The disparity between observed and uniform distributions: a new look at parasite aggregation.

              A simple new measure of parasite aggregation is described, the index of discrepancy (D). It quantifies the difference between the observed parasite distribution, and the hypothetical distribution that corresponds to the ideal case where all hosts harbour the same number of parasites. This index, computed for parasite distributions obtained from the literature, is compared to 2 other measures of aggregation, the variance to mean ratio and the parameter k of the negative binomial distribution. Both k and D indicate that aggregation decreases when the prevalence of infection and the mean number of parasites per host increase, while the variance to mean ratio suggests the opposite. Since an increase in prevalence means that parasites exploit a greater proportion of the available hosts and are thus not concentrating in only a few, aggregation should be inversely proportional to prevalence. Unlike k and D, the variance to mean ratio is a host-centered measure that is not very sensitive to the distribution of parasites. The index of discrepancy, on the other hand, is not only much easier to compute than k, but focuses on the difference between an ideal, uniform distribution and the one actually displayed by parasites. Since what it measures is what parasitologists mean by aggregation, the new index appears to be a more adequate measure of aggregation than other measures currently used.
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                Author and article information

                Journal
                Parasit Vectors
                Parasit Vectors
                Parasites & Vectors
                BioMed Central
                1756-3305
                2012
                7 March 2012
                : 5
                : 47
                Affiliations
                [1 ]School of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia
                [2 ]School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, UK
                [3 ]School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK
                Article
                1756-3305-5-47
                10.1186/1756-3305-5-47
                3364890
                22397763
                5ae64f51-09fc-462d-ab41-8d9905809237
                Copyright ©2012 Mohd Zain et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Research

                Parasitology
                rattus norvegicus,hymenolepis nana,nematodes,helminth species diversity,nippostrongylus brasiliensis,helminths,heterakis spumosum,rattus rattus,mastophorus muris,hymenolepis diminuta

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