Modeling of host genetics and resistance to infectious diseases: understanding and controlling nematode infections

This paper considers approaches to modeling the dynamics of infectious disease and the application of such models to nematode parasite infections in ruminants. Particularly, these models are developed to account for host genetics and may be used to assess the effects of using genetics to control nematode infections. Three main issues are critically examined: the infection transmission cycle from pasture to host to pasture, the expected genetic relationships between resistance and performance, and the risks of parasite evolution in response to genetic changes in the host. To obtain answers that are realistic and of practical use, the modeling approaches require a solid grounding in biology. This biology is formalized and described using mathematical techniques, with the models parameterized using experimental or field data. Transmission dynamics have been quantified by modeling and are backed by strong experimental data. Selection for resistance will be successful in reducing egg output, pasture larval contamination and hence subsequent larval challenge. Modeling frameworks have been developed to predict genetic relationships between resistance to infectious disease and performance in general, and genetic correlations predicted for nematode resistance are close to mean published values. These predicted correlations strengthen as the larval challenge increases and the dietary (protein) adequacy decreases, however modeling challenges remain. Lastly, although convincing experimental data is not yet available, arguments based on modeling suggest that the risks of parasite evolution in response to genetic changes in the host should be less than the risks arising from other control strategies, such as anthelmintics. Thus, modeling techniques predict that selective breeding for resistance should be an effective and sustainable complementary control measure.     

Analysis of the mucosal microenvironment: factors determining successful responses to mucosal vaccines

The predominance of IgA antibodies in mucosal sites reflects a combination of high rate IgA isotype switching among precursor cells in induction sites, their selective localisation in mucosal effector tissues and vigorous proliferation of these cells after extravasation. Each of these steps leading to IgA expression at the mucosa is under cytokine control. This paper will address the role of cytokines in induction and expression of IgA responses, the contribution of various precursor cell subsets and their differential responses to cytokine signals and strategies for manipulating cytokine expression. With respect to IgA antibody production in the gut whereas IL-4 and TGF-beta have been implicated in isotype switching of precursor cells to IgA commitment, their subsequent localisation, proliferation and effector activity expression is dependent on IL-5 and IL-6 expression locally. Most IgA plasma cells in the intestine derive from cells of the B2 lineage in the Peyer's patch, but a subpopulation of cells derived from the peritoneal cavity (B1 cells) also contribute to the IgA plasma cell population in the intestinal lamina propria. Whereas IgA+ cells of the B2 lineage are IL-6 dependent but IL-5 independent, B1-derived IgA+ cells are IL-5 dependent and IL-6 independent. On the other hand, cell mediated immune responses in the gut are highly dependent on IFN-gamma production by both Th1 CD4 cells and CD8 cells and in enteric Salmonella infection IFN-gamma production is essential but antibody has little effect on this process.Therapeutic interventions based on the information emerging from these studies will lead to improved vaccination responses and correction of immunodeficiencies especially in young animals.     

Anthelmintics used in treatment of parasitic infections of horses

The common anthelmintics used to treat parasitic infections of horses are described. Dosage, anthelmintic spectrum, formulation and administration, mode of action, toxicity contraindications, and resistance of parasites to anthelmintics are included.     

Advances in laboratory diagnosis of parasitic infections of sheep

Parasitic infections constitute an important group of diseases in sheep concerning the health status, welfare and productivity. On a global scale, there are considerable differences concerning the epidemiological situation with respect of the various parasite species. However, there are also numerous species, which occur on all continents and, potentially, in every country. Accordingly, the present review aims to providing an overview about the recent developments in methods and technologies for the laboratory diagnosis of parasite infections in sheep. Following in principle a systematic order the review encompasses publications addressing the diagnosis of helminthes (i.e., trematodes, cestodes and nematodes) and arthropod species. New approaches using conventional (e.g., microscopic), immunological and molecular techniques are being considered. The diagnosis of anthelmintic resistance is highlighted separately, due to its significant importance. The review ends with an outlook into the future by discussing most recent technological advances, which might become of use for the diagnosis of parasite infections in sheep in the future.     

Diagnostic methods for parasitic infections in livestock.

Parasitic infections are a primary cause of lost productivity in livestock world-wide. Accurate detection of parasites depends on many factors, including collection, storage, and transport of the sample, as well as the method of laboratory evaluation. However, the presence of a particular parasite does not always indicate the presence of parasitic disease. For many parasites, there exists a level at which the effect on production characteristics is balanced by the effect on the development of immunity. Interpretation of test results, therefore, should also consider such factors as the age of the animal or animals, clinical history, nutrition, local epidemiology of the parasites prevalent in the area, and any treatments that have been implemented.     

Bovine fascioliasis in Nigeria-intercurrent parasitic and bacterial infections

Summary The bacterial and parasitic infections associated with field cases of bovine fascioliasis due toFasciola gigantica were investigated; 47.6% of infected cattle had blood parasites, 61.9% had faecal-borne parasites and 85.8% had positive bacterial isolates in the bile in contrast to 13.3% with blood parasites, 71.1% with faecal-borne parasites and 28.9% positive for bile bacteria among uninfected cattle. Trypanosoma spp.,Babesia, Paramphistomum andSchistosoma were the most commonly found parasites associated with fascioliasis. On the other handStaphylococcus pyogenes, Escherichia coli and mixed infections of these with otherEnterobacteriaceae were the common bacteria isolated from the bile of infected cattle. The parasitaemia ofBabesia was significantly higher in infected than uninfected cattle but there was no significant difference in strongyle egg count between the 2 groups of cattle.

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Fascioliasis Bovina En Nigeria-Infecciones Intercurrentes Parasitarias Y Bacteriales

Resumen Se estudiaron las infecciones intercurrentes tanto parasitarias como bacteriales en casos naturales deFasciola gigantica; el 47.6% del ganado infectado tenía hemoparásitos, 61.9% tenía parásitos derivados de las heces fecales y en el 85.8% se hicieron aislamientos bacteriales positivos de la bilis. Esto en contraposición a 13.3% de hemoparásitos, 71.1% con parásitos derivados de las heces fecales y 28.9% aislamientos bacteriales positivos hechos de la bilis de ganado no infectado conF. gigantica.Los parásitos más comunmente asociados con fascioliasis fueronTrypanosoma spp.,Babesia, Paramphistomum y Schistosoma. Las bacterias aisladas de la bilis de ganado con fascioliasis fueron:Staphylococcus pyogenes, Escherichia coli, existiendo ambas también en forma mixta y asociadas con otras Enterobacteriaceas. La parasitemia conbabesia fue la más importante en ganado con fascioliasis. No hubo diferencia en los dos grupos de ganado (infectados y no infectados) en cuanto al conteo de huevos de especies de estrongilos.

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La Fasciolose Bovine Au Nigeria. Parasitisme Intercurrent Et Infections Bacteriennes

Résumé Les infections parasitaires et microbiennes associées à la fasciolose bovine naturelle due àFasciola gigantica ont été étudiées; 47,6 p. 100 des animaux infectés étaient porteurs de parasites sanguins, 61,9 p. 100 avaient des parasites fécaux et 85,8 p. 100 avaient des bactéries dans la bile contre respectivement 13,3 p. 100, 71,1 p. 100 et 28.9 p. 100 chez le bétail indemne de fasciolose. Trypanosoma spp.,Babesia, Paramphistomum etSchistosoma ont été les parasites les plus souvent associés avec la fasciolose. D'un autre côté,Staphylococcus pyogenes, Escherichia coli et des infections associées de ces derniers avec d'autres entérobactériacées ont été les bactéries les plus communément isolées de la bile ds animaux parasités. La parasitémie parBabesia a été significativement plus élevée chez le bétail infecté que chez le bétail sain, mais il n'y a eu aucune différence significative dans le nombre des oeufs de strongylidés entre les deux groups d'animaux.

     

New trends in parasitic infections of cultured freshwater fish

The 1980s are characterized by the appearance of new fish parasitoses, the clarification of the aetiology of diseases and new insights into the process of infection and the development of important parasites, especially myxosporidians. Two phaerosporoses have entered into the foreground: swimbladder inflammation (SBI) caused by Sphaerospora renicola in common carp and proliferative kidney disease (PKD) in salmonids. Both diseases must be reported in the German Democratic Republic (GDR). The connection between the "C-protozoa" in the blood and S. renicola in SBI was recently clarified by experiments by Molnar (1988). The results of our own investigations indicate that the "K-protozoa" phase of S. renicola parasitizes mainly the brain and sometimes the spleen, pancreas and liver before appearing in the swimbladder. Hedrick et al. (1988) in the USA and Odening et al. (1988b) in Europe first reported a Sphaerospora sp. in Salmo gairdneri in connection with PKD. The spectacular findings by Wolf and Markiw (1984) and El-Matbouli (1988) elucidating on the life cycle of Myxobolus cerebralis have not yet brought the revolutionary change expected for a general new estimation of myxosporidian transmission as a basis for ecotechnological control measures. Examples for the formation of new regionally specific parasite colonizations offer the far Eastern cyprinids introduced into Europe. In the GDR the silver carp is infected by Chloromyxum barbi (Myxosporidia) (Sedlazsek), the pathogenic Gyrodactylus sprostonae and two new Gyrodactylus species (Pectobathrii) (Lux). Eel parasites new to Europe are the obviously imported and highly pathogenic nematodes Anguillicola crassus and A. novaezelandiae (Paggi et al., 1982; Moravec and Taraschewski, 1988). In Central Europe the infestation of rainbow trout by the tapeworm Proteocephalus neglectus is increasing (Priemer, 1980; Hanzelova et al., 1988).     

Immunomodulation of host responses to ectoparasite infestation--an overview

Immune reactivity stimulated by ectoparasites and other arthropods has received increased attention in recent years. It is clear that a broad range of host responses are elicited, and immune effector mechanisms appear to be active in limiting infestation with blood-feeding arthropods. Host immune responsiveness appears to be altered as a consequence of infestation by certain arthropods, and the impact of these alterations on vector-borne pathogen transmission remains to be determined. Successful techniques have been developed by a number of investigators for the artificial induction of resistance to blood-feeding arthropods. These areas are examined in this paper.     

山羊寄生虫病联合用药效果观察

根据调查,对我县山羊危害严重的寄生虫病有:肝片吸虫病、食道口线虫病、疥螨病.笔者于2001年春在本县风华镇山羊中进行了联合用药驱虫试验.     

Survey of gastrointestinal parasitic infections in quarantined dogs in Taiwan

Intestinal helminth and protozoan infection in the quarantined dogs in Taiwan were examined using fecal examination between January to December, 2004. Of the 376 dogs imported from 11 countries, 63 (16.8%) were found to be infected with at least one species of intestinal parasite. The parasites detected were oocysts of Isospora canis and eggs of Toxocara canis, Trichuris vulpis and hookworms. Of the 63 infected dogs, 11 were found to have a mixed infection of two different species of parasites. This paper illustrates that parasites are transmitted from one country to another through the transport of animals. Moreover, there is also a possibility of parasitic infection among quarantined dogs as well as the zoonotic potential for quarantine officers during the quarantine period.     

A model for predicting parasitic gastroenteritis in lambs subject to mixed nematode infections

A model previously developed for the prediction of parasitic gastroenteritis in lambs arising from infection by the nematode parasite Ostertagia circumcincta has been adapted to consider mixed infection and retested. The importance of the lambs as a contributing source to the summer wave of infective larvae is highlighted as are certain apparent deficiencies in the use of grass sampling techniques as a means of assessing pasture larval contamination.     

Basophil leucocytes in responses to parasitic infection and some other stimuli in sheep

Basophil leucocytes are a significant component of the infiltrating cells in a variety of tissue reactions in guinea pigs. However, little is known about the participation of basophils in similar reactions in most other animal species. The circulating blood, skin and small intestinal mucosa of sheep were examined after they had received stimuli known to elicit basophil-rich responses in guinea pigs but relatively few basophils were found.     

Anthelmintic resistance in the field: Changes in resistance status of parasitic populations in response to anthelmintic treatment

Changes in anthelmintic resistance in nematode parasites were monitored in sheep grazing on 2 separate farms, but with the same anthelmintic treatment program, over 16 years. High levels of benzimidazole resistance emerged in Ostertagia and Trichostrongylus spp populations on both farms following 9 years of continuous use of this class of drug. Subsequently, variations in the levels of resistance occurred for the same species between farms and between species on the same farm. A change to levamisole for 2 years resulted in a significant reversion towards benzimidazole susceptibility, but a concomitant rise in levamisole resistance, in Ostertagia on one farm. However, benzimidazole resistance increased rapidly following the re-introduction of oxfendazole into the anthelmintic treatment program. Results from both farms illustrate the pitfalls of using one anthelmintic class for an extended period and provide indirect support for the alternation of anthelmintic classes at approximately yearly intervals.