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At least 307 records · Page 17Linked to original sources
PubMed2006

Population biology of multispecies helminth infection: competition and coexistence.

The role that interspecific interactions play in shaping parasite communities is uncertain. To date, models of competition between helminth species have assumed that interaction occurs through parasite-induced host death. To our knowledge, there has been no theoretical exploration of other forms of competition. We examine models in which competition acts at the point of establishment within the host, and at the time of egg production by the adult worm. The models used are stochastic and we allow hosts to vary in their rate of exposure to infective larvae. We derive the Lotka-Volterra model of competition when exposure is homogenous and thus demonstrate that two helminth species cannot coexist on a single limiting resource. We show that coexistence of species is promoted by heterogeneity in host exposure provided that the rates of exposure to the two species are not perfectly correlated, and, if they are positively correlated, provided that the degree of heterogeneity in host exposure is similar for the two competing helminth species. These results are robust to the mechanism of competition.

Animals↗
PubMed2002

Expansion of NK cells with reduction of their inhibitory Ly-49A, Ly-49C, and Ly-49G2 receptor-expressing subsets in a murine helminth infection: contribution to parasite control.

Natural killer cell-associated direct cytotoxicity and cytokine production are crucial mechanisms for early innate host resistance against viruses, bacteria, or protozoa. The engagement of inhibitory NK cell receptors can influence host responses to viruses. However, these receptors have not been investigated to date in parasitic infections, and little is known about the role of NK cells in the defense against helminths. Therefore, we have correlated the frequencies of cells expressing the pan-NK marker DX5 and subsets bearing inhibitory Ly-49 receptors with worm survival and cytokine production during infection with Litomosoides sigmodontis in BALB/c mice (H2(d)), the only fully permissive model of filariasis. A marked influx of DX5(+)/CD3(-) NK cells and DX5(+)/CD3(+) T cells into the pleural cavity, where the parasites were located, was observed. The frequency of pleural NK cells expressing the H2(d)-reactive inhibitory receptors Ly-49A, Ly-49C, or Ly-49G2 declined most strongly compared with spleen and blood. In the peripheral blood, longitudinal analysis revealed an early and stable reduction of Ly-49C(+) and Ly-49G2(+) NK cells, a subsequent significant increase of the entire NK cell and DX5(+)/CD3(+) T cell populations, and a reduction in the Ly-49A(+) subset. The in vivo depletion of NK cells strongly enhanced the worm load and influenced IL-4 and IL-5 plasma levels. These data demonstrate a new role for NK cells in the host defense against filariae and, for the first time, alterations of Ly-49 receptor-expressing NK cell subsets in a parasitic infection.

Animals↗
PubMed2004

Mouse mast cell protease-1 is required for the enteropathy induced by gastrointestinal helminth infection in the mouse.

BACKGROUND & AIMS: The relationship between intestinal pathology and immune expulsion of gastrointestinal nematodes remains controversial. Immune expulsion of gastrointestinal helminth parasites is usually associated with Th2 responses, but the effector mechanisms directly responsible for parasite loss have not been elucidated. Mast cell hyperplasia is a hallmark of infection with gastrointestinal nematodes, in particular Trichinella spiralis. Although the precise mechanism by which mast cells induce expulsion of these parasites has not been elucidated, it has been proposed that mast cell mediators, including cytokines and granule chymases, act to create an environment inhospitable to the parasite, part of this being the induction of intestinal inflammation. Therefore, the aims of this study were to dissect the role of mast cells and mast cell proteases in the induction of parasite-induced enteropathy. METHODS: Mast cell-deficient W/Wv and mouse mast cell protease-1 (mMCP-1)-deficient mice were infected with T. spiralis, and parasite expulsion, enteropathy, and Th2 responses were determined. RESULTS: Expulsion of the parasite was delayed in both strains of mice compared with wild-type controls; additionally, in both cases, the enteropathy was significantly ameliorated. Although Th2 responses were significantly reduced in mast cell-deficient W/Wv mice, those from mMCP-1-deficient mice were similar to wild-type mice. Additionally, levels of TNF-alpha and nitric oxide were significantly reduced in both W/Wv and mMCP-1 deficient mice. CONCLUSIONS: These results imply that mast cells may contribute to the induction of protective Th2 responses and, importantly, that the intestinal inflammation associated with gastrointestinal helminths is partly mediated by mMCP-1.

Animals↗
PubMedDate not supplied

The distribution of intestinal helminth infections in a rural village in Guatemala.

Fecal egg count scores were used to investigate the distribution and abundance of intestinal helminths in the population of a rural village. Prevalences of the major helminths were 41% with Ascaris lumbricoides, 60% with Trichuris trichiura and 50% with Necator americanus. All three parasites showed a highly aggregated distribution among hosts. Age/prevalence and age/intensity profiles were typical for both A. lumbricoides and T. trichiura with the highest worm burdens in the 5-10 year old children. For hookworm both prevalence and intensity curves were convex in shape with maximum infection levels in the 30-40 year old age class. Infected females had higher burdens of T. trichiura than infected males in all age classes of the population; there were no other effects of host gender. Analysis of associations between parasites within hosts revealed strong correlations between A. lumbricoides and T. trichiura. Individuals with heavy infections of A. lumbricoides and T. trichiura showed highly significant aggregation within households. Associations between a variety of household features and heavy infections with A. lumbricoides and T. trichiura are described.

Adolescent↗
PubMed1986

The population dynamics of acquired immunity to helminth infection.

Based on experimental evidence we develop and exploit a mathematical model to describe the role of acquired immunity in host-helminth interactions. We show that the model gives a quantitative description of the population dynamics in a laboratory situation involving a host immunological response. We make practical predictions based on these results.

Animals↗