Pathogenic Helminths Research Articles

State of the Art Review: An Epidemiological Approach to the Health Effects of Wastewater Reuse

The reuse of wastewaters for agricultural irrigation can be a means of reducing the pollution of surface waters including those in coastal areas used for bathing. The wastewater stream of a community carries within it the complete spectrum of pathogenic bacteria, viruses, protozoa and helminths which are endemic in the community. These pathogens can survive sufficiently long in the soil or on crops to infect, at least in theory, persons coming in direct contact. Thus, it is important to establish a sound epidemiological basis for health regulations related to the reuse of wastewater in agriculture. This paper presents the theoretical epidemiological considerations that should serve as the basis for a predictive model of the potential risks associated with wastewater irrigation. Empirical data from credible, quantifiable epidemiological studies have here been reviewed to validate the theoretical model. For developing countries, the authors have concluded that the ranking of pathogens as to the degree of risk associated with wastewater irrigation is as follows: high risk - helminths, medium risk - bacteria and protozoa and low risk - viruses.In order to effectively reduce the concentration of these pathogens wastewater treatment is recommended as the most effective control strategy.

Cell-Mediated Damage to Helminths

Although it is difficult to draw any sweeping conclusions that would be applicable to all helminth infections, the main features that are emphasized in this review may be summarized briefly. Pathogenic helminths, although extremely diverse in structure and behaviour, have one common feature, namely that they present to the host's defenses large, non-phagocytosable surfaces. Because of this, they are susceptible to a range of effector mechanisms differing either quantitatively or qualitatively from those that are active against other parasites or against normal or abnormal host cells. As an extreme example, the various types of cytotoxic lymphocyte, with one interesting exception, are inactive against helminths. Instead, helminth infections are characterized by high IgE responses and increased numbers of circulating eosinophils. Such eosinophils are activated, and show a marked capacity to kill a variety of target helminths in vitro. Further activation may occur in response to mast cell mediators released as a result of IgE-dependent degranulation; and IgE, as well as IgG and complement, can mediate eosinophil attachment and killing. It may therefore be suggested that the eosinophil/IgE/mast cell axis represents a powerful host defense against helminth infections. IgE can also mediate macrophage-dependent killing of several helminths, a process which involves a functional change in the macrophage, resembling activation. Although eosinophil-mediated and IgE-dependent macrophage-mediated effects are particularly potent, other effector cells are not excluded: in certain circumstances, neutrophils and conventionally activated macrophages may be equally or more effective. Neutrophils appear to act solely by oxidative killing mechanisms, whereas degranulation and the release of toxic granule contents is equally or more important in eosinophil-mediated damage. Different stages of different helminths vary in their degree of susceptibility to different mechanisms. Eosinophils appear to be somewhat less active than neutrophils against ensheathed nematodes, whereas trematodes and exsheathed nematodes are highly susceptible to eosinophil attack. In many experimental helminth infections, studies in vivo suggest a role for antibody-dependent cell-mediated immune effector mechanisms. The identity of the effector cell is difficult to establish because of a lack of techniques for specific manipulation of individual cell types, but histological studies frequently point to a strong eosinophil or macrophage involvement. The development and analysis of in vitro assays allows the study of immune effector mechanisms in man.(ABSTRACT TRUNCATED AT 400 WORDS)

Hygienic Quality of Sewage Sludge Compost

The numerous bacterial, viral, protozoal, helminthic and fungal pathogens in sewage are concentrated in raw sewage sludge during primary sedimentation. Anaerobic digestion, air-drying and activated sludge treatment may reduce the levels of these organisms, but a risk to human health still remains. Although the magnitude of this risk cannot be quantified or even predicted at this stage, the probability of infection must be minimised to protect the community. Composting reduces the health hazard by decreasing the virulence (numbers and viability) of pathogenic organisms. Results of experiments conducted by the NIWR showed that total coliforms, E. coli, coliphage, Salmonella and Ascaris ova can be eliminated in less than a week in a pilot-scale composter utilising dewatered raw and air-dried digested sludges with wood chips and refuse as filler material. In full-scale plants elimination of indicator organisms took much longer, depending on the degree of control exercised.

RODENT ZOONOSES IN NORTH QUEENSLAND

A study of potentially zoonotic infections was carried out on 351 rodents trapped in north-eastern Queensland. Their ecosystems included towns, agricultural and livestock areas, wookland and rainforest. Nine serotypes of salmonellae were obtained from asymptomatic carries in predominantly settled locations. Two strains of Ps. pseudomallei occurred in rainforest near Innisfail and one on a cattle property adjacent to Townsville. Ps. aeruginosa caused bronchopneumonia in one animal from Townsville harbour. Ifection by leptospirae of six serogroups and seven serovars were identified by serological or cultural examinations. Enzootic foci occurred on the Mount Spec rainforest where celledoni and australis were being excreted by rats adjacent to the Paluma dam system. In addition to the scrub typhus locations at Rocky Creek, Atherton Tableland and Bullocky Creek, near Ingham, which were confirmed, a new focus of infection by R. tsutsugamushi was identified at El Arish near Tully. Water rat (H. chrysogaster) at Townsville harbour constituted a reservoir of toxoplasmosis. In addition to the known human pathogenic helminths H. nana and H. diminuta, localized foci of hookworms (Ancylostoma spp.) were found. Histological evidence of cytomegalic disease of the salivary glands or kidneys was a common finding.

Purification of Schistosoma mansoni egg antigens: theory and practice.

With the current burgeoning of interest in the immunology of parasitic disease, parasite immunochemistry is finally beginning to come of age. In the 1960s immunochemical research was primarily concerned with identifying serological antigens. Methods such as immunodiffusion and immunoelectrophoresis found acceptance among those interested in schistosomiasis and application to that parasitic infection. In the late 1970s emphasis has fallen on the purification of parasite antigens with special emphasis on their characterization and biological properties. Considerable progress on fractionating protozoal antigens has been made, culminating in the elegant studies of Cross et al. characterizing the molecular structure of the trypanosome surface coat antigens. In non-protozoal helminth systems, studies of Echinococcus granulosus have identified the immunodominant antigens which have proven useful in the serodiagnosis of human disease. However, research on the major helminth pathogen of man, Schistosoma, has neither equalled the molecular elegance of trypanosome work nor achieved the practical consequences of Echinococcus immunochemistry.

The library of spatial structure models of tubulins from pathogenic worms

Aim. The aim of this work is to create library of pathogenic helminths tubulin 3D-models. Created models will be used as targets for in silico screening of new anthelmintic compounds. Methods. Tubulin sequences were obtained from UniProtKB database. Modeling of spatial structure of the proteins was performed using I-TASSER server. Optimization of three-dimensional models geometry was performed in Gromacs using amber03 force field. Results. Based on Uni-ProtKB database analysis, 302 amino acid sequences of α- (105), β- (170) and γ-tubulins (27) of pathogenic worms were selected. 3D-models of selected proteins were built using base protocol. Conclusions. A built 3D models of pathogenic worms tubulins were deposited in CSModDB (http://csmoddb.ifbg.org.ua/comodore/index.php) database. Created library of 3-D structures are suitable for further usage in VO CSLabGrid virtual screening for new compounds.
 Keywords: tubulin, pathogenic worms, database, Grid.

STUDIES ON THE GROWTH OF TROUT, SALMO TRUTTA FROM FOUR CONTRASTING HABITATS

An ecological investigation was undertaken at four contrasting stations on three river systems in West Wales, namely the Teify, the Rheidol and the Pysgotwr, with a view to evaluating the effect of ecological factors, particularly the helminth parasites, on the growth of the trout. When compared with the larger, faster growing trout from the two stations (A and B) on theTeify the slow‐growing trout from the other two stations (C and D). located in each of the more acid rivers, were characterized by a lower specific growth rate, a more restricted growing season, a lower condition factor, less fat on the pyloric caeca and earlier maturation of the gonads. The diet of the smaller, slow‐growing trout contained e smaller proportion of large, readily accessible food and seemed to be more adversely influenced by the effect of floods and the onset of winter than was the case with trout at the other stations. There was no evidence that poor growth of trout in the more acid streams wm due to the effect of helminth parasites. Of the thirteen species of helminths encountered in the trout at Stations A and B only three occurred commonly at Stations C and D and the only demonstrably pathogenic helminths, namely the acanthocephalan Neoechinorhynchw tutili and the plerocercoid larva of Diphyllobothrium were conspicuously absent. The growth of the trout appeared to be a function of several components of the ecosystem. Favourable productivity indices include a pH of approximately 7 or more, a high ionic and calcium content, a large area of depositing substratum, a low susceptibility to sudden flooding, a favourable temperature regime (Brown, 1946 c), a rich growth of algae and phanerogams. a wide variety and high density of animals including those of a large size and high accessibility and finally a rich fauna of helminth parasites particularly nematoda and acanth6cephala.

On the Potential Longevity of Various Helminths with a Record for a Species of Trichostrongylus in Man

With few possible exceptions, parasitic worms do not pass more than one generation within their host, increase in the intensity of an infection being contingent upon the introduction of additional infective larvae from without. Consequently a knowledge of the natural, or normal, life-span of the parasite may determine the desirability of treating individual cases of infestation or may indicate the procedure that should be adopted in controlling the parasite on a larger scale. With a short-lived and not highly pathogenic helminth, it may be more politic to elaborate plans for the prevention of reinfection than to resort to medicinal treatment that may not always be efficacious and is sometimes accompanied by an element of danger to the host. On the other hand, when dealing with a long-lived parasite, widely distributed in a community or in a herd of animals, it is desirable to couple efforts to control the parasite in its extra-corporeal phase with treatment of the individual carriers. In several instances where agricultural live stock is involved, knowledge of the longevity of the parasite in its adult and free-living stages has led to the practice of seasonal administration of anthelmintics. Important as information on this phase of helminth bionomics is recognized to be, dependable data is available for only a few of the long list of economically significant species. That such lacunae in our otherwise comprehensive knowledge of the biology of most of the common helminths should still persist is readily to be understood when it is realized how difficult of attainment are the conditions necessary to supply reliable information. The time when the infection became established must be known, at least approximately, and the infection must be followed continuously with the host adequately protected against reinfection or superinfection. Conditions which provide these requirements are difficult to secure where parasites of the lower animals are involved. But with certain parasites of man infections have sometimes been imposed experimentally to yield the desired information. Light has also been shed on this question by following cases of infection after the subject has left the region where the infection was contracted to reside in a region where reinfection cannot occur. Consequently more is known about the longevity of various species of human helminths than those of other animals.