Immunology and immunopathology of helminth infections.

A short review is presented describing the novel immunological concepts related to vaccine development. Trichinella is used as an example.     

Comparative histochemical observations on the excretory system of helminth parasites.

The excretory canals of Ascaridia galli (Nematoda) and the protonephridial ducts of Cotylophoron cotylophorum (Trematoda) and Raillietina cesticillus (Cestoda) have been studied with regard to the histochemical localization of lipids, carbohydrates and hydrolytic enzymes. Distinct excretory organs are absent in the acanthocephalan Centrorhynchus corvi. Triglycerides, phospholipids and lipoproteins are seen in association with the wall of excretory canals of A. galli and R. cesticillus, and phospholipids and lipoproteins at the corresponding site in C. cotylophorum. The physiological significance of lipids in association with excretion of substances has been discussed. Low molecular weight glycogen is present in the lumen of excretory canal of A. galli but not in other worms. The common feature of the excretory canals is the presence of enzyme activities of nonspecific alkaline phosphatase and Mg2+-dependent ATPase. Activity of acid phosphatase is seen only in the excretory canals of A. galli. Glucose-6-phosphatase is present in A. galli and C. cotylophorum and absent in R. cesticillus. Weak reaction of 5'-nucleotidase is present in the excretory canals of helminth species studied here. The role of these enzymes in transportation of substances across the wall of excretory canals and also in ionic regulation has been discussed in detail.     

Lymphoid cell responses in parasitic helminth infections.

The cellular responses during experimental ascariasis provide a mechanism whereby effector systems are mobilized rapidly and locally, resulting in the prompt response which is evident on reinfection. It is proposed that the products of activated "T" lymphocytes facilitate local accumulation of lymphoid cells which, later, as specific antibody-producing cells provide the mediators (e.g. opsonizing antibody) responsible for mechanisms which destroy the parasite. While the mechanisms causing death of the parasite are still unknown, our present studies will provide an explanation of events that prepare for this event.     

Ecology of helminth communities in tropical Australian amphibians.

Less than 50% of Australian amphibians have been recorded as hosts for helminth parasites. Despite developments in parasite community ecology in amphibians elsewhere, Australia lags behind with only two publications on this subject. Reasons advanced for this are that much of the collecting and taxonomic studies were conducted earlier this century before more recent discoveries of host genera and species as well as species complexes in the amphibian fauna. Consequently, there is a need for re-collection of hosts and parasites, and taxonomic revision of the parasites. In addition, as shown in this study, the parasite fauna in Australian amphibians is depauperate. Composition of the parasite fauna was largely dependent on the ecological associations of the host animal species. Frogs were infected with few helminth species and these occurred at low intensity, indicating, as in Europe and North America, that a depauperate fauna is also characteristic of amphibians in tropical regions.     

Emerging helminth zoonoses

As our ability to recognise and diagnose human disease caused by helminth parasites has improved, so our understanding of the epidemiology and clinical manifestations of these diseases has improved. Humans can develop patent infection with a wide range of helminth parasites, whose natural host is another vertebrate. Rather than focusing on a comprehensive review of zoonotic helminth infections, this review describes in detail examples of zoonotic helminth infections that have newly appeared in human populations, or have existed but are increasing in incidence or geographic range. Examples include intestinal capillariasis, anisakidosis, eosinophilic enteritis, oesophagostomiasis and gnathostomiasis. Potential reasons for the emergence of these infections, including changes in social, dietary or cultural mores, environmental changes, and the improved recognition of heretofore neglected infections often coupled with an improved ability to diagnose infection are discussed.     

Phylogenetics and the future of helminth systematics

Phylogenetic systematics is a relatively new formal technique that increases the precision with which one can make direct estimates of the history of phylogenetic descent. These estimates are made in the form of phylogenetic trees, or cladograms. Cladograms may be converted directly into classifications or they may be used to test various hypotheses about the evolutionary process. More than 20 phylogenetic analyses of helminth groups have been published already, and these have been used to investigate evolutionary questions in developmental biology, biogeography, speciation, coevolution, and evolutionary ecology.     

G-quadruplexes in helminth parasites

Parasitic helminths infecting humans are highly prevalent infecting ∼2 billion people worldwide, causing inflammatory responses, malnutrition and anemia that are the primary cause of morbidity. In addition, helminth infections of cattle have a significant economic impact on livestock production, milk yield and fertility. The etiological agents of helminth infections are mainly Nematodes (roundworms) and Platyhelminths (flatworms). G-quadruplexes (G4) are unusual nucleic acid structures formed by G-rich sequences that can be recognized by specific G4 ligands. Here we used the G4Hunter Web Tool to identify and compare potential G4 sequences (PQS) in the nuclear and mitochondrial genomes of various helminths to identify G4 ligand targets. PQS are nonrandomly distributed in these genomes and often located in the proximity of genes. Unexpectedly, a Nematode, Ascaris lumbricoides, was found to be highly enriched in stable PQS. This species can tolerate high-stability G4 structures, which are not counter selected at all, in stark contrast to most other species. We experimentally confirmed G4 formation for sequences found in four different parasitic helminths. Small molecules able to selectively recognize G4 were found to bind to Schistosoma mansoni G4 motifs. Two of these ligands demonstrated potent activity both against larval and adult stages of this parasite.     

The structure of helminth communities

The existence of both interactive and isolationist communities of helminths, each of which may be produced by any one of several processes, necessitates a pluralistic view of helminth community structure. A scheme involving three hierarchical scales of communities of helminths is proposed. Interactions between species occur in infracommunities, and should be looked for there. Interactions are often clearer in smaller groups of species, either among core species or within guilds. Infracommunities are samples of helminth communities at two larger scales: the helminth community in the host population provides core species, largely specialists, and that in the host community provides the generalists and the satellite species. The richness of each of the two large-scale communities is affected by various ecological, historical and evolutionary factors. The different concepts which have been applied to parasite communities are based on these factors.     

Replicating helminth parasites of man

Most helminth parasites of man are unable to replicate within the human host. Thus, the worm burden of an infected person (on which the pathology largely depends - see Box 1) is a function of the number of infective forms to which the person is exposed. But for some species of helminths, the ability to replicate in man has a marked effect on the course and duration of infection, and for the pathogenesis of disease. In this review, David Grove discusses the mechanisms by which such replication may occur, and considers how this ability affects our approach to therapy and control.     

Parasites of Salmo trutta L. from the Tirino River. II. Host-parasite interactions of helminth species

The hundred and sixteen brown trout (Salmo trutta L.) which were examined for helminth parasites were captured in the River Tirino, (L'Acquila - Italy). Six parasite species (Phyllodistomum simile, Crowcrocaecum testiobliquum, Crepidostomum metoecus, Cyathocephalus truncatus, Truttaedacnitis truttae and Dentitruncus truttae) were recovered. Ecological studies on each helminth species recovered have been carried out analysing the following aspects; the preference of each parasite species for certain microhabitats in the host; the incidence and intensity of each parasitic infection according to sex, age and season.     

Neuromuscular electrophysiology of the filarial helminth Dipetalonema viteae

1. A body wall preparation is described which permits intracellular recording from the somatic muscle cells of the small filarial nematode, Dipetalonema viteae. Using this preparation, resting membrane potentials were measured and spontaneous muscle depolarizations described. 2. Stimulatory effects noted upon the addition of acetylcholine, or the cholinergic agonists suggest the hypothesis that acetylcholine is the excitatory neurotransmitter. However, in contrast with vertebrate tissues, the cholinergic antagonists, d-tubocurarine, hexamethonium and pentolinium do not inhibit somatic muscle activity of the worm. 3. GABA inhibited somatic muscle depolarizations, suggesting the possibility that it may serve as an inhibitory neurotransmitter. 4. The anthelmintic drug, levamisole, produced a depolarizing block. Effects of other pharmacological agents are described, discussed and compared with effects on vertebrate muscles.