Infections with Ascaris lumbricoides, Triclmris trichiura and the hookworm species are often found in the same communities and individuals. Hosts infected by more than one species are potentially at risk of morbidity associated with each infection. This paper describes the use of a probabilistic model to predict the prevalence of multiple-species infections in communities for which only overall prevalence data exist. The model is tested against field data, using log-linear analysis, and is found to be more effective at estimating the numbers of multiple infections involving hookworms than those involving only A. lumbricoides and T. trichiura. This latter combination of infections is found, in half the communities examined, to be more common than expected by chance. An age-stratified analysis reveals that the degree of interaction between these two infections does not alter significantly with age in the child age classes of a Malaysian population.

The pharyngeal component of the enteric nervous system of the parasitic nematode, Ascaris suum exhibits immunoreactivity for serotonin (5-hydroxytryptamine or 5-HT) and for FMRFamide-like peptides. This paper describes the application of an in vitro pharmacological approach to investigate the functional role of 5-HT and FMRFamide-like peptides. The pharyngeal pumping behaviour of Ascaris suum was monitored using a modified pressure transducer system which measures pharyngeal pressure changes and therefore pumping. The pharynx did not contract spontaneously; however, 5-HT (10-1000 μM) stimulated pumping at a frequency of 0·5 Hz. FMRFamide had no apparent effect on pharyngeal pumping. The native nematode FMRFamide-related peptide (FaRP), KSAYMRFamide inhibited the pumping elicited by 5-HT. The duration of inhibition was dose-dependent (0·1-1000 nM) with a threshold of 0·1 nM. In 4 preparations, the inhibition of the pharyngeal muscle was preceded by an initial excitation and increase in the amplitude of pharyngeal pressure changes. The pharynx is involved in various nematode processes, including feeding, regulation of hydrostatic pressure and excretion. The role of 5-HT and KSAYMRFamide in the pharyngeal function of nematodes is discussed.

The cuticle of adult forms of Strongyloides venezuelensis was studied by routine transmission electron microscopy, conventional freeze-fracture and also using quick-freeze and deep-etch techniques. In routine thin sections the cuticle of S. venezuelensis comprises 7 layers: epicuticle, outer cortical, inner corticcal, external medial, internal medial, fibrous and basal. Observation of replicas of specimens fractured across the thickness of the body wall, revealed at the epicuticle an ordered array of particles accompanying the cuticular annulations. At the level of the cortical and medial layers we observed few scattered particles embedded in an amorphous matrix without a particular arrangement. The fibrous layer was represented by several parallel lines of ordered particles of similar size. In tangentially fractured specimens, the epicuticle cleaves readily exposing 2 faces, one exhibiting intramembranous particles without any particular arrangement, immersed in a smooth matrix (P face), and the other showing depressions and very few particles (E face). In replicas of fractures submitted to etching, we observed at the level of the cortical, medial fibrous and basal layers an interconnecting fibrous and globous structure which was organized in a different direction at the fibrous layer. The association of freeze-fracture to deep-etch technique revealed the internal structural organization of the cuticle layers showing details that were not seen before using conventional freeze–fracture technique.

We combined polymerase chain reaction (PCR) amplification of DNA sequences and important morphological characters as a technique to differentiate nematode isolates in the genus Steinernema. Five decamer oligonucleotide primers were used to generate random amplified polymorphic DNA (RAPD) fragments from 11 nematode isolates. The primers generated 8–12 fragments, ranging from 220 to 1300 bp in size. Reproducible amplified DNA fragments of 11 isolates showed obviously inter- or intra-specific polymorphisms, enabling us to differentiate easily the nematode species and isolates. Combining RAPD–PCR fragments with the examination of morphological characters of infective juveniles and 1st-generation males, we identified isolate OH1S, collected from Newport, Oregon, as S.feltiae; isolate OS21, collected from Grants Pass, Oregon, belonged to a previously undescribed species. Our study may provide a rapid and reliable method for the identification of Steinernema nematodes.

A stochastic simulation model of the transmission and maintenance of genetic heterogeneity in the absence and presence of external selection pressures is presented for polygamous intestinal helminths such as Ascaris. The model assumes that the density distribution of the adult parasites is highly aggregated and that density-dependent effects on fecundity are important. The model gives rise to stable infection rates in the host. Where the parasite population contains genetic heterogeneity, with the exception of stochastic fluctuations which models genetic drift, the ratio of the different alleles remained constant over extended periods of time. This result contrasts with that of an earlier analytical model (Anderson, R. M., May, M. R. & Gutpa S. (1989) Parasitology 99, S59–S79), in which uneven mating probabilities for the different combinations of worm possible in a host was postulated to inevitably lead to fixation of the most abundant allele. New results suggest that in spite of the restricted choice of mating available to a worm in the confines of a host, selection pressure always leads to enrichment of the parasites carrying resistant alleles.

Antibody responses to Ascaris lumbricoides worm antigens were examined by ELISA in a case-control study of 2 groups of Bangladeshi children, one of which had been shown over a period of 12 months to be consistently lightly infected (controls) and the other consistently heavily infected (cases). The children showed a wide range in intensity of infection; children identified as cases were on average 4 times more heavily infected than the controls. There were no significant differences in weight, height, mid-upper arm circumference and skinfold thickness between the case or control subjects at the time blood samples for analyses by ELISA were collected. Children with repeatedly heavy infections with A. lumbricoides had higher concentrations of antibody isotypes to the antigens of A. lumbricoides than children who are repeatedly lightly infected. IgG1, IgG4 and IgE to worm antigens occurred in significantly higher concentrations in heavily infected subjects. This suggests that these antibody responses simply reflect the intensity of infection and may not play a significant role in protecting against heavy infections.

Plasticity of gp63 gene organization in Leishmania (Viannia) braziliensis and Leishmania (Viannid) peruviana Parasitology (1995), 111, 265–273

Fig. 4 (p. 270) was wrongly orientated. It appears correctly below.

Fig. 4. RFLP analysis after digestion with Bgl I and hybridization with pLb-134Sp (A) or the 10 kb Not I/Bgl I recombinant fragment of cosmid clone B.3.4.2 (B). Isolates: Leishmania braziliensis M2904, 1; L. peruviana LC26, 2. Size is expressed in kb.

This investigation compared the effect of two common types of diet on worm burdens and faecal egg counts of pigs inoculated with Ascaris suum and Oesophagostomum dentatum. The diets were both considered nutritionally sufficient for pigs of this age, and gave high and comparable growth rates. Pigs were inoculated with both worm species at 14 weeks of age and slaughtered 3 or 12 weeks later. At 3 weeks, A. suum larvae were numerous in the small intestine of pigs fed ground barley plus protein supplement, but were not detected from pigs fed a commercial full-constituent pelleted feed. At 12 weeks, however, average adult worm burdens were low and similar in both groups. At both slaughter times, O. dentatum worm burdens were significantly higher in pigs fed barley plus protein than in pigs given commercial feed, particularly for female worms, and the commercial diet led to worms being located further along the large intestine, and to reduced worm fecundity. The chemical composition of large intestinal contents differed significantly between pigs fed the two diets.

The previous paper in this issue Computer model of the maintenance and selection of genetic heterogeneity in polygamous helminths by Saul uses an individual-based computer simulation to explore aspects of the transmission and maintenance of genetic heterogeneity among polygamous intestinal helminths, both in the absence and in the presence of external selection pressures resulting from chemotherapy. Saul finds that, in the absence of any selective effects, genetic heterogeneity persists, contradicting the results presented by Anderson, May & Gupta (1989) that mating probability functions create density-dependent and frequency-dependent selective pressures against a rare allele, which eventually leads to its elimination.

The effect of two types of diet on populations of Ascaris suum and Oesophagostomum dentatum in experimentally infected pigs Parasitology (1995), 111, 395–402

Part of the reference list that was omitted from p. 402 appears below.