The interaction between the 2 nodular worm species in the pig, Oesophagostomum dentatum (O.d.) and Oesophagostomum quadrispinulatum (O.q.), was studied by comparing the development and distribution of the species following single or mixed infections. The faecal egg excretion levels were assessed at regular intervals from week 3 post-inoculation, and indicated a strong negative impact of the introduction of O.q. on the continued egg excretion of O.d. All pigs were killed 9 weeks after the first inoculations to determine the composition and location of the worm burdens in the large intestine. O.q. was found more anteriorly located in the intestine than O.d., thus confirming previous descriptions. When both species were present, the distribution of O.d. was moved further posteriorly and was more spread out than in single-species infections. There appeared to be no adverse effect of O.d. on the establishment and fecundity of O.q. However, the worm recoveries corroborated the egg excretion observations, namely reduced worm burdens of O.d. if O.q. was introduced, or if O.q. was already present. It is uncertain whether this effect is caused by differences in host reaction against the two species, or whether a more specific competition occurs between the two nodular worm species in pigs.

Infection with developing metacestodes of the rat tapeworm, Hymenolepis diminuta, is known to retard the accumulation of the yolk protein, vitellin, in the terminal ovarian follicles of the intermediate host, Tenebrio molitor. It is probable that this is the result of competitive inhibition of juvenile hormone binding at a microsomal binding site in the beetle follicular epithelium. Experiments were designed to test the hypothesis that inhibitor molecules were circulating in the haemolymph of infected beetles. Whole haemolymph, collected from male or female beetles at various stages post-infection, was injected into non-infected female recipients 2 days post-emergence. Ovaries were removed 3 days later and the vitellin content of the same sized follicles measured using an ELISA. The vitellin content of follicles from recipients of haemolymph from females infected with metacestodes at stage 1 and stage 3–4 was significantly reduced (24 and 27·9%) compared to sham-infected females. However, haemolymph from females infected with mature metacestodes did not affect the vitellin content. Results were thus comparable to those obtained by monitoring ovarian vitellin levels in female T. molitor with bona fide infections. Haemolymph from infected males did not affect ovarian vitellin content. These results indicate that molecules that can modulate vitellogenesis may be present in the haemolymph of females infected with developing metacestodes but that these factors disappear later in infection.

We have investigated the effects of host age and sex on human antibody isotype responses to Schistosoma mansoni and Schistosoma japonicum adult worm (AW) and soluble egg (SEA) antigens, using sera from subjects in Kenya and the Philippines. Similar trends with age were observed between the two populations despite host, parasite and environmental differences between the two geographical locations. IgE to AW increased with age, whereas most isotype responses to SEA decreased with age. IgG1, IgG3 and IgG4 subclass responses to adult worm, however, did not show a broadly rising or falling pattern with age. Males were found to have higher IgG1, IgG4 and IgE to AW in both populations. This sex difference remained significant in the Kenyan population even after controlling statistically for confounding factors such as age and differences in intensity of infection. Analysis of S. mansoni and S. japonicum adult worm antigens reactive with IgE revealed a predominant 22 kDa band in both parasites. Only those individuals with relatively high IgE titres specifically reactive with S. mansoni or S. japonicum AW had detectable IgE against Sj22 or Sm22.

The composition, richness and similarity of helminth communities in a tropical freshwater fish were determined in samples of Cichlasoma urophthalmus collected from 7 localities of broadly similar age and character situated along the northern coast of the Yucatan peninsula, Mexico. The component communities exhibited a unique combination of characteristics for a freshwater fish. They were dominated by digeneans, with all other helminth groups being numerically inferior. A common suite of species could be recognized, but many of its members were generalists and not cichlid specialists. Species richness and number of individuals per host were high, but diversity was low, reflecting high dominance by one species. Intra- and inter-locality similarity levels were low, and local variation high. In respect of species richness and digenean dominance, the communities resembled those in Australian tropical anguillids, but in respect of low diversity, similarity and high dominance they are more similar to helminth communities of northern temperate fish.

This paper reviews sites of action of anthelmintic drugs including: (1) levamisole and pyrantel, which act as agonists at nicotinic acetylcholine receptors of nematodes; (2) the avermectins, which potentiate or gate the opening of glutamate-gated chloride channels found only in invertebrates; (3) piperazine, which acts as an agonist at GABA gated chloride channels on nematode muscle; (4) praziquantel, which increases the permeability of trematode tegument to calcium and results in contraction of the parasite muscle; (5) the benzimidazoles, like thiabendazole, which bind selectively to parasite β-tubulin and prevents microtubule formation; (6) the proton ionophores, like closantel, which uncouple oxidative phosphorylation; (7) diamphenethide and clorsulon, which selectively inhibit glucose metabolism of Fasciola and; (8) diethylcarbamazine, which appears to interfere with arachidonic acid metabolism of filarial parasites and host. The review concludes with brief comments on the development of anthelmintics in the future.

Part of the Cε3–Cε4 region of the ovine immunoglobulin E (IgE) gene (nucleotides 1111–1575) was amplified by PCR. The recombinant protein (recIgE1-2) was expressed in E. coli and both monoclonal and polyclonal antibodies were produced. These antibodies recognized recIgE1-2 and native IgE on Western blots and in ELISA. The polyclonal serum showed cross-reactivity with other sheep immunoglobulin classes. The monoclonal antibody was specific for ovine IgE and goat IgE. Infection of sheep with the abomasal nematode Haemonchus contortus resulted in elevated IgE levels in serum 2–4 weeks after infection, as measured by sandwich ELISA using the rabbit polyclonal as capture antibody and the monoclonal antibody against ovine IgE as second antibody. A negative correlation between worm counts and total serum IgE levels at the end of the experiment was found in repeatedly infected sheep. Significant increased levels of excretory–secretory antigens specific IgE levels were found after H. contortus infection. In contrast, no significant changes in 3rd-stage larvae (L3) antigen-specific IgE titre in sera could be detected after infection.

We suggest a new mechanism for the maintenance of specificity of the association between the entomopathogenic nematode Steinernema scapterisci and its symbiotic bacteria. We evaluated the development and reproduction of infective and non-infective juvenile S. scapterisci in monoxenic combinations with its symbiotic bacteria, Xenorhabdus sp. ‘S’ and with the bacterial symbiont of Steinernema carpocapsae and Steinernema riobravis. Although development of non-infective stages occurred on all Xenorhabdus spp., the development of infective juveniles to the 4th stage (‘dauer’ recovery) was significantly delayed and reduced with X. nematophilus and Xenorhabdus sp. ‘R’, the bacterial symbionts of S. carpocapsae and S. riobravis, respectively. ‘Dauer’ recovery improved significantly when the cultures of X. nematophilus and Xenorhabdus sp. ‘R’ were supplemented with cell-free filtrates from Xenorhabdus sp. ‘S’. The infective juvenile S. scapterisci produced in all 3 cultures were virulent to Galleria mellonella larvae, confirming successful retention of Xenorhabdus from other steinernematids in their intestine. In fact, S. scapterisci infective juveniles containing X. nematophilus or Xenorhabdus sp. ‘R’ were more virulent to G. mellonella than those containing their natural symbiont, Xenorhabdus sp. ‘S’. We believe that this is the first demonstration of the symbiont-specific exit of infective juveniles from the ‘dauer’ phase which represents the finest level of specificity of bacteria–nematode association. This is also the first report of successful isolation of the natural symbiont of S. scapterisci.

The time-course of differentiation/proliferation of mast cells in gut epithelium was investigated in mice infected with the nematode Strongyloides venezuelensis. After infection, expression of proliferating cell nuclear antigen increased in gut intraepithelial mast cells on days 7 to 11, followed by an increase in the number of intraepithelial mast cells from days 11 to 14. Mast cell precursors were defined as cells that formed mast cell colonies in methylcellulose culture. After infection, the numbers of mast cell precursors in the population of gut intraepithelial mononuclear cells (IEMNC) increased significantly on day 3 and returned to the pre-infection level by day 7. Mast cell precursors in Peyer's patches, mesenteric lymph nodes (MLN), and spleen also increased from day 7 p.i. Production of IL-3 and IL-4 in MLN and spleen were increased between 7 and 11 days p.i. These results show that murine intestinal mastocytosis is initiated by an early increase in mast cell precursor number in the gut epithelium followed by proliferation/differentiation of mast cells. Mast cell precursor numbers increased even before the production of IL-3 and IL-4 in MLN and spleen, suggesting that some local factors might be involved in this phenomenon.

The drug cyclosporin A (CsA) exerts its immunosuppressive action by binding to the cytosolic protein, cyclophilin (CyP) and, as a complex, binding to and inhibiting the calcium/calmodulin-dependent serine threonine phosphatase, calcineurin. It is unknown whether a similar mode of action occurs during the drug's antiparasite activity. Calmodulin-binding proteins from the helminth parasites Hymenolepis microstoma and H. diminuta were purified by affinity chromatography, yielding single polypeptide bands of 60000 Mr, according to SDS–PAGE. These proteins were tested for calcineurin activity by the dephosphorylation of the RII peptide (part of the catalytic subunit of cAMP-dependent protein kinase). Both proteins were calcium- and calmodulin-dependent and were inhibited by mammalian cyclophilin complexed with cyclosporin A (IC50 values of 0·75 μg CyP for H. microstoma and 0·90 μg CyP for H. diminuta). However, neither of the parasite calcineurins was inhibited by H. microstoma cyclophilin/CsA. These data suggest the anthelmintic mode of action of CsA in these helminth models does not involve the inhibition of a signal transduction pathway requiring interaction with calcineurin.

The lateral diffusion (DL) properties of the fluorescent lipid probe 5-N (octadecanoyl) aminofluorescein (AF18) inserted into the surface of muscle-stage larvae of Trichinella spiralis were investigated by fluorescence recovery after photobleaching. AF18 was not free to diffuse laterally in dormant larvae, and this remained unchanged after larval activation in vitro with trypsin and bile. However, a significant increase in surface fluidity of the probe was demonstrated (%R = 74·5; DL = 11·5 × 10−9 cm2/sec) when larvae invaded intestinal epithelial tissue following oral infection of mice. Membrane-permeant photoactivatable caged cyclic AMP was used to analyse the putative mechanism responsible for this increase in lateral diffusion in the parasite surface. Although incubation of larvae with 1–50 μM caged cAMP had no effect on surface fluidity, incubation with 100 μM caged cAMP induced a substantial increase in the lateral mobility of AF18 (%R = 64·3; DL = 8·3 × 10−11 cm2/sec) immediately following photo-activation of the caged messenger. This induced fluidity, however, was transient and the larval surface reverted to immobility within 15 min. These observations constitute the first reported measurement of the fluid properties of the surface of intracellular parasites, the first demonstration of the parasite surface fluidity altering as a result of host cell invasion and the first indication of a mechanism underlying changes in surface fluidity in parasitic helminths.

Infective juveniles (IJs) of Steinernema carpocapsae (All) are able to remain relatively highly infective even when they have almost exhausted their neutral lipid reserves. This is not seen in other steinernematid species so we proposed that carbohydrate may be important for infectivity in aging IJs of S. carpocapsae. The present study investigated glycogen utilization in IJs of 4 entomopathogenic nematodes, S. carpocapsae, S. riobravis (Biosys 355), S. feltiae (UK76) and S. glaseri (NC), stored in distilled water at 25 °C. The 4 species had appreciable amounts of glycogen; from ca. 8% dry weight in S. riobravis to ca. 18% in S. glaseri. Infective juveniles of S. carpocapsae and S. riobravis survived for 120–135 days and utilized ca. 90% of their glycogen reserve at an almost constant rate during a 112-day storage period. Steinernema feltiae and S. glaseri lived for much longer (>450 days) and during a 250-day storage period their glycogen content decreased by 27 and 40%, respectively. In contrast to the other 3 species, the rate of lipid decline preceded that of glycogen in S. carpocapsae. The rate of glycogen decline in S. carpocapsae IJs incubated with the glycolytic inhibitor, iodoacetamide (10−4 M) was significantly reduced (P<0·05) compared with untreated nematodes, and the infectivity of inhibitor-treated aged (>80 days) IJs was reduced compared with controls. Incubating aged (80-day) IJs of S. carpocapsae (mean neutral lipid content ca. 10% of initial level) with 10−4 M iodoacetamide for 24 h significantly reduced (P<0·05) their infectivity compared with freshly harvested inhibitor-treated IJs and untreated controls. Following an 11-day recovery period, the infectivity of inhibitor-treated aged IJs recovered significantly (P<0·05). The evidence suggests that glycogen is an important source of energy for maintaining infectivity in aged IJs of S. carpocapsae.

An 8-point visual index was developed for Oil Red O staining of neutral lipids in infective juveniles (IJs) of Steinernema carpocapsae (All), S. riobravis (Biosys 355), S. feltiae (UK76) and S. glaseri (NC). The visual index was found to be a reliable and rapid method for determining the relative neutral lipid content of individual IJs and was validated quantitatively by gas chromatography. The relationship between neutral lipid utilization and infectivity of IJs stored in distilled water at 25°C was also investigated and the first quantitative results on neutral lipid utilization in entomopathogenic nematodes are reported. Neutral lipid contents of freshly harvested IJs of S. carpocapsae, S. riobravis, S. feltiae and S. glaseri were 31, 31, 24 and 26% dry wt, respectively. Steinernema carpocapsae showed a sigmoidal pattern for neutral lipid utilization while S. riobravis used neutral lipids at an almost constant rate. Survivorship of these two species ranged between 120 and 135 days, whereas S. feltiae and S. glaseri lived >450 days and had a slower rate of lipid utilization during a 260 day storage period. Oil Red O staining showed that individual IJs in each population utilized lipids at different rates, even though they had the same initial lipid index. The infectivity of S. riobravis, S. feltiae and S. glaseri declined with lipid utilization. In contrast, S. carpocapsae maintained a high level of infectivity even at relatively low lipid levels. Therefore, neutral lipid content was found to be a suitable indicator of infectivity for S. riobravis, S. feltiae and S. glaseri but not for S. carpocapsae.

The humoral immune response of roach (Rutilus rutilus) to cercariae of the digenean trematode, Rhipidocotyle fennica, was studied. Antibodies against R. fennica were found in wild roach in lakes where fish are infected by the parasite. Antibody levels were higher in sera collected in September than in sera collected in June, due to infection of R. fennica during the late summer. In experimental aquarium studies, roach immunized with homogenized cercariae produced antibodies against R. fennica. An especially strong response was elicited by infecting fish with living cercariae emerging from infected clams. The specificity of the antibodies, as shown in Western blots, was different between fish immunized with homogenized cercariae and those fish infected with living cercariae. The specificity and amount of antibodies depended on the route of immunization. The challenge experiment with R. fennica indicated that previous infection of fish gives some protection against R. fennica.

A characteristic feature of infections with the nematode parasite of mice Heligmosomoides polygyrus, is a marked IgG1 hypergammaglobulinaemia. A possible source for this immunoglobulin has recently been demonstrated, through evidence that H. polygyrus adult worm homogenate (AWH) can induce the in vitro production of non-specific IgG1 from mouse lymphocytes. To determine the interactions between this immunoglobulin and the parasite, the ability of IgG1 to bind to AWH of H. polygyrus was investigated. Protein (Western) blotting indicated that mouse monoclonal antibodies are able to bind non-specifically to selected parasite antigens. Furthermore, by binding H. polygyrus adult worm homogenate to cyanogen bromide (CNBr)-activated Sepharose CL-4B, an affinity column was prepared which could be used to efficiently purify mouse IgG1 monoclonal antibodies. These antibodies were eluted from the affinity column and still retained their original specificity. These results indicate that H. polygyrus not only induces the production of non-specific IgG1 by the host, it can also bind this immunoglobulin to its own specific proteins. Thus, it is possible that IgG1 produced during a primary infection with H. polygyrus may not entirely benefit the host.

Helminthologically naive 8-week-old lambs were administered 50000 infective-stage larvae of the trichostrongyle nematode Nematodirus battus. Initial mean adult worm burdens were significantly reduced (P < 0·01) at day 21 post-infection (p.i.). Peripheral blood eosinophil counts showed a significant increase (P < 0·001) by day 25 p.i. when compared with uninfected control animals. Sections of small intestine taken at post-mortem from the area of adult worm establishment over the course of infection showed a significant increase in mucosal eosinophil and mast cell numbers during the period of adult worm rejection, when compared with uninfected control animals. These results show that young lambs develop significant increases in the numbers of cells associated with an inflammatory reaction in the intestine during the development of a partially protective immune response to this parasitic nematode.

Despite considerable therapeutic success with the antimalarial 4-aminoquinolines such as chloroquine, there is serious doubt about the future of this drug class due mainly to the development and spread of parasite resistance throughout endemic areas. In this article we review the possible biochemical and molecular basis of resistance. Based on our current understanding we have considered the possibility of developing strategies which may allow the aminoquinolines to once again be used effectively against P. falciparum. Our conclusions are that drug resistance is the result of a reduced rate of drug uptake which in turn reduces the amount of drug available to bind the target. The basis for this reduced accumulation could be an altered pH gradient making the food vacuole more alkaline or the parasite cytosol more acidic, an efflux pump removing drug directly from the membrane or any other process which will reduce the rate of drug uptake. Central to the effectiveness of this resistance mechanism is the transient availability of a high affinity, low capacity drug binding site (possibly haem) within the parasite. Resistance reversers such as verapamil influence the apparent Ka for this drug binding phenomenon via an increased drug uptake rate. We demonstrate that by chemical modification of the aminoquinolines, producing predictable alterations in their physicochemical properties, that it is possible to minimise the verapamil sensitive component of resistance and reduce significantly cross-resistance patterns without loss in absolute activity. Based on these views we suggest that the aminoquinoline antimalarials still have a role to play in the cheap, safe and effective chemotherapy of falciparum malaria.

Parasite life-history traits should reflect past environmental and host-related selective pressures acting to produce strategies that maximize transmission success. The evolution of adult body size and egg production in 804 species of trematode parasites was investigated using independent contrasts derived from a phylogeny of trematodes. Contrasts in trematode body size were positively correlated with contrasts in egg size, and almost significantly correlated with contrasts in numbers of uterine eggs. After controlling for body size, no relationship existed between egg size and egg numbers, suggesting that there is no trade-off between the two components of egg production. Average host body mass and latitude of the sampling site did not correlate with either trematode body size or egg size. Contrasts between trematode taxa exploiting ectotherm hosts and their sister taxa exploiting endotherms showed no consistent difference in either body size or egg size. The effect of other variables on trematode life-histories, such as the nature of the habitat in which eggs are released, the site of attachment within the host's body, or the number of hosts involved in the life-cycle, could not be evaluated statistically. The similarity in life-history traits among members of given clades suggests that phylogenetic constraints may have acted to limit or mask any adaptive changes expected from changes in host-related or environmental conditions.

Parasitic helminths (worms) cause serious infectious diseases in humans and domestic animals. Control of these infections relies mostly on chemotherapeutics (the anthelmintics), but resistance has developed against most of these broad-spectrum drugs in many parasite species. These resistant parasites are being used to elucidate the molecular mechanisms of drug resistance and drug action. This has led to the development of sensitive assays to detect resistant parasites, but this has not delayed the emergence of additional drug resistant parasite populations. Therefore, as development of new drugs by pharmaceutical companies is slow, we may have to be prepared for a time when broad-spectrum drugs are no longer effective, especially against worms of sheep.

The intermediate hosts for Taenia saginata and T. solium are cattle and pigs (and humans for the latter), respectively. In vitro-hatched (but not activated) oncospheres of both Asian Taenia (T. saginata asiatica, a new subspecies of T. saginata or T. asiatica, a new species) and T. solium injected subcutaneously into the backs of mice with severe combined immunodeficiency (scid) developed into fully matured cysticerci. Five-month-old metacestodes of Asian Taenia had no hooklets and were bigger in size than those previously reported and similar to those of T. saginata. Their morphology suggested that the cysticerci were more advanced than those in the intermediate host animals. It is suggested that scid mice are valuable experimental animal models for studying human taeniid cestode infections.

Partially purified low molecular weight antigens obtained by gel filtration of whole worm homogenates or total adult excretory–secretory (ES) products were tested in a vaccination experiment to determine their ability to induce protective immunity against Haemonchus contortus in sheep. Sheep were challenged with 20000 infective 3rd-stage larvae. One animal in the low molecular weight vaccinated group showed no protection against H. contortus, whereas the 4 other sheep in this group showed a mean reduction of 99·9% in faecal egg counts and of 97·6% in abomasal worm burden compared to the non-vaccinated controls and the adjuvant controls. The ES-vaccinated sheep showed a 32·2% reduction in parasite egg production and a 63·7% reduction in abomasal worm counts. Analysis of the humoral immune responses revealed no significant differences in antibody recognition of putative protective antigens between the protected and non-protected vaccinated animals. However, a marked lower lymphocyte proliferation response was found in non-protected sheep.