Distribution patterns and microhabitat segregation in gastrointestinal helminths of Sorex shrews

We studied the distribution patterns and microhabitat use in gastrointestinal helminths of the shrews Sorex araneus and S. caecutiens in Finland. The distribution of species prevalences was bimodal, and in S. araneus the abundance (mean intensity) was positively associated with commonness (prevalence), as assumed by the core-satellite species hypothesis (Hanski 1982). However, the positive correlation between prevalence and intensity was observed only when the effects of helminth body size and taxonomic group (cestodes vs nematodes) on intensity were controlled for. The nematodes of the genus Longistriata occurred predictably as core species, whereas the identity of the core cestodes was more variable between host species and regions. Helminth body size and taxonomic group were not related to the degree of aggregation in shrew populations, but helminth body size seemed to explain the differences in the distribution patterns of helminths between shrews and voles. The core species did not show more segregation in microhabitat use than randomly selected species. In fact, the two core nematodes showed largely overlapping intestinal distributions. We conclude that linear intestinal space is not a key resource for shrew nematodes, but it may be for shrew cestodes.     

Helminth Collection and Identification from Wildlife

Wild animals are commonly parasitized by a wide range of helminths. The four major types of helminths are "roundworms" (nematodes), "thorny-headed worms" (acanthocephalans), "flukes" (trematodes), and "tapeworms" (cestodes). The optimum method for collecting helminths is to examine a host that has been dead less than 4-6 hr since most helminths will still be alive. A thorough necropsy should be conducted and all major organs examined. Organs are washed over a 106 μm sieve under running water and contents examined under a stereo microscope. All helminths are counted and a representative number are fixed (either in 70% ethanol, 10% buffered formalin, or alcohol-formalin-acetic acid). For species identification, helminths are either cleared in lactophenol (nematodes and small acanthocephalans) or stained (trematodes, cestodes, and large acanthocephalans) using Harris'' hematoxylin or Semichon''s carmine. Helminths are keyed to species by examining different structures (e.g. male spicules in nematodes or the rostellum in cestodes). The protocols outlined here can be applied to any vertebrate animal. They require some expertise on recognizing the different organs and being able to differentiate helminths from other tissue debris or gut contents. Collection, preservation, and staining are straightforward techniques that require minimal equipment and reagents. Taxonomic identification, especially to species, can be very time consuming and might require the submission of specimens to an expert or DNA analysis.     

Removal of adult cyathostomins alters faecal microbiota and promotes an inflammatory phenotype in horses

The interactions between parasitic helminths and gut microbiota are considered to be an important, although as yet incompletely understood, factor in the regulation of immunity, inflammation and a range of diseases. Infection with intestinal helminths is ubiquitous in grazing horses, with cyathostomins (about 50 species of which are recorded) predominating. Consequences of infection include both chronic effects, and an acute inflammatory syndrome, acute larval cyathostominosis, which sometimes follows removal of adult helminths by administration of anthelmintic drugs. The presence of cyathostomins as a resident helminth population of the equine gut (the “helminthome”) provides an opportunity to investigate the effect helminth infection, and its perturbation, has on both the immune system and bacterial microbiome of the gut, as well as to determine the specific mechanisms of pathophysiology involved in equine acute larval cyathostominosis. We studied changes in the faecal microbiota of two groups of horses following treatment with anthelmintics (fenbendazole or moxidectin). We found decreases in both alpha diversity and beta diversity of the faecal microbiota at Day 7 post-treatment, which were reversed by Day 14. These changes were accompanied by increases in inflammatory biomarkers. The general pattern of faecal microbiota detected was similar to that seen in the relatively few equine gut microbiome studies reported to date. We conclude that interplay between resident cyathostomin populations and the bacterial microbiota of the equine large intestine is important in maintaining homeostasis and that disturbance of this ecology can lead to gut dysbiosis and play a role in the aetiology of inflammatory conditions in the horse, including acute larval cyathostominosis.     

The relationship between species richness and productivity in metazoan parasite communities

Biodiversity is not distributed homogeneously in space, and it often covaries with productivity. The shape of the relationship between diversity and productivity, however, varies from a monotonic linear increase to a hump-shaped curve with maximum diversity values corresponding to intermediate productivity. The system studied and the spatial scale of study may affect this relationship. Parasite communities are useful models to test the productivity-diversity relationship because they consist of species belonging to a restricted set of higher taxa common to all host species. Using total parasite biovolume per host individual as a surrogate for community productivity, we tested the relationship between productivity and species richness among assemblages of metazoan parasites in 131 vertebrate host species. Across all host species, we found a linear relationship between total parasite biovolume and parasite species richness, with no trace of a hump-shaped curve. This result remained after corrections for the potential confounding effect of the number of host individuals examined per host species, host body mass, and phylogenetic relationships among host species. Although weaker, the linear relationship remained when the analyses were performed within the five vertebrate groups (fish, amphibians, reptiles, mammals and birds) instead of across all host species. These findings agree with the classic isolationist-interactive continuum of parasite communities that has become widely accepted in parasite ecology. They also suggest that parasite communities are not saturated with species, and that the addition of new species will result in increased total parasite biovolume per host. If the number of parasite species exploiting a host population is not regulated by processes arising from within the parasite community, external factors such as host characteristics may be the main determinants of parasite diversity.     

Fasciola hepatica cathepsin L-like proteases: biology,function, and potential in the development of first generation liver fluke vaccines

Fasciola hepatica secretes cathepsin L proteases that facilitate the penetration of the parasite through the tissues of its host, and also participate in functions such as feeding and immune evasion. The major proteases, cathepsin L1 (FheCL1) and cathepsin L2 (FheCL2) are members of a lineage that gave rise to the human cathepsin Ls, Ks and Ss, but while they exhibit similarities in their substrate specificities to these enzymes they differ in having a wider pH range for activity and an enhanced stability at neutral pH. There are presently 13 Fasciola cathepsin L cDNAs deposited in the public databases representing a gene family of at least seven distinct members, although the temporal and spatial expression of each of these members in the developmental stage of F. hepatica remains unclear. Immunolocalisation and in situ hybridisation studies, using antibody and DNA probes, respectively, show that the vast majority of cathepsin L gene expression is carried out in the epithelial cells lining the parasite gut. Within these cells the enzyme is packaged into secretory vesicles that release their contents into the gut lumen for the purpose of degrading ingested host tissue and blood. Liver flukes also express a novel multi-domain cystatin that may be involved in the regulation of cathepsin L activity. Vaccine trials in both sheep and cattle with purified native FheCL1 and FheCL2 have shown that these enzymes can induce protection, ranging from 33 to 79%, to experimental challenge with metacercariae of F. hepatica, and very potent anti-embryonation/hatch rate effects that would block parasite transmission. In this article we review the vaccine trials carried out over the past 8 years, the role of antibody and T cell responses in mediating protection and discuss the prospects of the cathepsin Ls in the development of first generation recombinant liver fluke vaccines.     

The reliability of observational approaches for detecting interspecific parasite interactions: comparison with experimental results

Interactions among coinfecting parasites have the potential to alter host susceptibility to infection, the progression of disease and the efficacy of disease control measures. It is therefore essential to be able to accurately infer the occurrence and direction of such interactions from parasitological data. Due to logistical constraints, perturbation experiments are rarely undertaken to directly detect interactions, therefore a variety of approaches are commonly used to infer them from patterns of parasite association in observational data. However, the reliability of these various approaches is not known. We assess the ability of a range of standard analytical approaches to detect known interactions between infections of nematodes and intestinal coccidia (Eimeria) in natural small-mammal populations, as revealed by experimental perturbations. We show that correlation-based approaches are highly unreliable, often predicting strong and highly significant associations between nematodes and Eimeria in the opposite direction to the underlying interaction. The most reliable methods involved longitudinal analyses, in which the nematode infection status of individuals at one month is related to the infection status by Eimeria the next month. Even then, however, we suggest these approaches are only viable for certain types of infections and datasets. Overall we suggest that, in the absence of experimental approaches, careful consideration be given to the choice of statistical approach when attempting to infer interspecific interactions from observational data.     

Taenia crassiceps infection and its excreted/secreted products inhibit STAT1 activation in response to IFN-γ

It is well understood that helminth infections modulate the immune responses of their hosts but the mechanisms involved in this modulation are not fully known. Macrophages and dendritic cells appear to be consistently affected during this type of infection and are common target cells for helminth-derived molecules. In this report, we show that macrophages obtained from chronically Taenia crassiceps-infected mice displayed an impaired response to recombinant murine IFN-γ, but not to recombinant murine IL-4, as measured based on the phosphorylation of STAT1 and STAT6, respectively. These macrophages expressed high levels of SOCS3. However, the inhibition of phosphatase activity by orthovanadate restored the IFN-γ response of these macrophages by increasing STAT1 phosphorylation without affecting SOCS3 expression. Therefore, we aimed to identify the phosphatases associated with IFN-γ signaling inhibition and found that macrophages from T. crassiceps-infected mice displayed enhanced SHP-1 expression. Interestingly, the exposure of naïve macrophages to T. crassiceps excreted/secreted products similarly interfered with IFN-γ-induced STAT1 phosphorylation. Moreover, macrophages exposed to T. crassiceps excreted/secreted products expressed high levels of SOCS3 as well as SHP-1. Strikingly, human peripheral blood mononuclear cells that were exposed to T. crassiceps excreted/secreted products in vitro also displayed impaired STAT1 phosphorylation in response to IFN-γ; again, phosphatase inhibition abrogated the T. crassiceps excreted/secreted product-altered IFN-γ signaling. These data demonstrate a new mechanism by which helminth infection and the products derived during this infection target intracellular pathways to block the response to inflammatory cytokines such as IFN-γ in both murine and human cells.     

Australian ecosystems, capricious food chains and parasitic consequences for people

Characteristic Australian ecosystems or environments contain numerous food chains some of which may become capriciously side-tracked or appropriated by humans, with parasitic consequences for people in Australia and overseas. Twelve of 13 arboviruses affecting humans are of wildlife origin and all are transmitted by mosquitoes. In this case, transmission is thus associated with aquatic environments, many artificial. Zoonotic trematode (brachylaimiasis) and cestode (rodentoleposis) infections have been reported from semi-arid environments. Scabies and angiostrongylosis are associated with work, recreational and home environments. Four species of Rickettsia endemic in wildlife are acquired by humans from fleas, mites and ticks in bush and semi-urban environments. The enigmatic and life-threatening muspiceoid nematode, Haycocknema perplexum, is known from people associated with the natural environment in Tasmania; whether it comes from vertebrates, invertebrates, plants, soil or water is unknown. Food chains occurring in a range of Australian ecosystems and environments, some associated with feeding arthropods, others with accidental ingestion of invertebrates, may result in human exposure and infection. A range of organisms normally occurring in wildlife, domestic animals or the environment may be involved in causing human disease.     

Sarcoptic mange in wild carnivores and its co-occurrence with parasitic helminths in the Western Italian Alps

Between 2001 and 2004, 229 foxes, 36 stone martens and 48 badgers from the western Italian Alps were examined for sarcoptic mange and for gastrointestinal helminths to investigate their prevalence and geographical distribution and to point out the existence of potential interactions among them. Sarcoptic mange was observed in 25.3±2.8% SE of foxes and in 5.6±3.8% SE of stone martens, while no badger was found infected. Helminths belonged to Cestoidea Cyclophillidea (3.0±1.1% SE), Nematoda Trichurida (Capillaria aerophila and Trichuris vulpis: 6.5±1.6% SE; Trichinella britovi: 3.0±1.1% SE), Ascaridida (12.2±2.2% SE) and Strongylida (6.9±1.7% SE). Sarcoptic mange infection and the presence of helminths proved to be associated, with mangy foxes showing significantly higher prevalence of both cestode and nematode (particularly Ascaridida) worms. Moreover, considering three clusters of parasites (S. scabiei, nematodes and cestodes), more foxes than expected hosted simultaneously 2 and 3 taxa. These evidences suggest the existence of some kind of interaction, whose modalities and implications are discussed in this paper.