Three groups of anthelmintic drugs act directly and selectively on muscle membrane receptors of parasitic nematodes. These groups of anthelmintics are: (1) The Nicotinic Agonists(levamisole, pyrantel, morantel and oxantel) that act on acetylcholine receptors of nematode somatic muscle; (2) The GAB A Agonist, piperazine, that acts on nematode muscle GABA receptors; and (3) The Avermectins that open glutamate gated Cl- channels on nematode pharyngeal muscle. The electrophysiology and pharmacology of muscle and neuromuscular transmission the nematode parasite, Ascaris suum, is outlined and effects of anthelmintics that interfere with transmission described. Resistance to anthelmintics has appeared in some parasitic nematodes but the mechanisms of this resistance remain to be determined

Steinernema carpocapsae (Rhabditida: Steinernematidae) host recognition behaviour was assessed and compared with 2 measures of host suitability. Previous research showed that S. carpocapsae infective juveniles respond to host cues in a hierarchical order, with attraction to Galleria mellonella volatiles being stimulated by contact with G. mellonella cuticle. We measured host recognition behaviour by calculating the percentage response of S. carpocapsae infective juveniles to volatiles produced by G. mellonella last instars after the nematodes were exposed to the cuticle of 11 candidate arthropod hosts and 2 control surfaces. Host suitability was measured by nematode-induced mortality to candidate hosts at 2 nematode doses and the level of reproduction supported by each host. The highest recognition response was scored for Agrotis ipsilon (Lepidoptera: Noctuidae). This insect also incurred nearly 100% mortality due to nematode infection and supported the highest level of reproduction. Non-insect arthropods tested (Chilopoda and Isopoda) stimulated no behavioural response and were not susceptible to nematode infection. Other insect species elicited intermediate levels of the recognition response. There were significant correlations between behavioural response and nematode-induced mortality at the lower dose. The level of reproduction supported by the candidate hosts was also correlated with S. carpocapsae behavioural response.

A detailed morphological investigation of the anterior sensory organs, the nerve ring and a glomerulus-like structure in male Onchocerca volvulus was performed by means of electron microscopy. The 8 head papillae are arranged in the common 4 + 4 pattern of most filarial worms in circles around the mouth opening. The amphidial openings are found between the circles of inner and outer papillae on both sides of the mouth. Inside, several additional nerve axons are seen in the tissue of the anterior tip not related to one of the identified papillar structures. The inner and outer papillae exhibit a remarkably different fine structure, and are part of a complex system of at least 2 different receptor cell types at the anterior tip of the worm. The amphidial channel contains 8 modified cilia; accessory axons are associated with the cytoplasm of the sheath cell. The anterior nerve ring of male worms is located about 150 µm posterior from the outermost tip of the head region. It consists of several fibres coiled around the oesophagus. The comparison of the fine structure of the central nervous system did not show the expected morphological differences associated with the heterogeneous age distribution in the natural worm population. This was in contrast to previous findings with respect to tissues in different parts of the worm. The study also provides the first evidence that suggests the existence of an excretory organ in a filarial worm in the region of the anterior nerve ring. Paired glomerulus-like structures in the lateral chords and a canal formed by a projection of the basal zone of the cuticle were identified.

A study to compare the effects of different frequencies of targeted chemotherapy with levamisole (Ketrax: JAGAL Pharma, Lagos, Zeneca Pharmaceuticals UK) as an action for the control of Ascaris lumbricoides was carried out in 3 communities in rural Oyo State, Nigeria. The targeted group comprised children, aged 5 to 15 years, attending primary school within their village. Treatment was provided within the school with the assistance of the school teachers. Three frequencies of targeted treatment were offered. In one village targeted treatment was provided on 1 occasion in 1 year, in another village at two 6-monthly intervals and in the third village every 4 months. Prevalence and intensity (e.p.g.) of A. lumbricoides infection were determined immediately before and after the period of intervention using a modified Kato–Katz technique. In the villages which received treatment once and at 6-monthly intervals, a reduction in post-treatment intensity of A. lumbricoides was observed in the total population but this failed to attain statistical significance. In contrast, within the village which received 4-monthly targeted chemotherapy, a significant reduction in post-treatment intensity of A. lumbricoides was observed in the total population and in the targeted children. In general, reductions in the intensity of A. lumbricoides after intervention were not particularly pronounced in untreated children (aged 0–4 years) even in the 4-monthly targeted village, whereas in untreated adults, reductions approached statistical significance in villages which received targeted treatment once and at 4-monthly intervals.

Density-dependent effects of Anguillicola crassus larval infections in the copepod intermediate host were examined experimentally. Three species of copepods (Cyclops vicinus, C. viridis and C. fuscus) were subjected to a range of doses of larval A. crassus within infection arenas. Prevalence, intensity and parasite dispersion (variance: mean abundance) values increase and then approach an asymptote as infection dose increases. Infection parameters differ between species of copepod. Increasing temperature has a negative effect on the establishment of the parasite population within the intermediate host. Parasite-induced host mortality increases with dose. These mechanisms have the potential to regulate populations of A. crassus larvae within the copepod population and hence the whole suprapopulation.

A cDNA clone encoding a full length putative collagen has been isolated in a screen of a mixed stage Globodera pallida expression library. Comparison of the deduced amino acid sequence of this molecule with other collagens suggests it is a cuticular collagen and a member of the col-8 subfamily of collagen genes. Northern blots show the gene is expressed specifically in gravid, adult females of the parasite as compared to second (invasive) stage juveniles and virgin females. Preliminary immunocytochemical studies indicate this collagen is present in areas other than the cuticle; these findings and the potential functional role of this collagen are discussed.

The nematode nervous system employs many of the same neurotransmitters as are found in higher animals. The inactivation of neurotransmitters is absolutely essential for the correct functioning of the nervous system, In this article we discuss the various mechanisms used generally in animal nervous systems for synaptic inactivation of neurotransmitters and review the evidence for similar mechanisms operating in parasitic and free-living nematodes. The sequencing of the entire Caenorhabditis elegans genome means that the sequence of nematode genes can be accessed from the C. elegans database (ACeDB) and this wealth of information together with the increasing knowledge of the genetics of this free-living nematode will have great impact on all aspects of nematode neurobiology. The review will provide an insight into how this information may be exploited to identify and characterize target proteins for the development of novel anti-nematode drugs.

We used selection to test for a genetic component to the pattern of emergence of infective juveniles from the host cadaver in the entomopathogenic nematode, Steinernema glaseri (Steiner), and whether other traits would respond to selection on this major and complex life-history character. We selected for early (‘ fast’) and late (‘ slow’) emerging lines by perpetuating nematodes that emerged on the first and after the seventh day of emergence respectively. After 12 cycles of selection, the pattern for the slow line but not the fast line differed significantly from the base population. Cumulative emergence for the slow line was less than the base population from Days 4 to 14 of the 18-day emergence period. The maximum difference occurred on the fourth day when 72·6% of emergence was complete for the base population but only 55·4% for the slow line. Decreases in infective juvenile size over the emergence period were consistent with the change in emergence pattern, but variation in sex ratios was not. No differences in infectivity were found. These results indicate that the emergence pattern has a genetic component, and that genetic variability for this trait occurs in natural populations. Furthermore, the asymmetric response to selection suggests that our field population is under strong selection for a highly skewed early emergence.

Appetite and growth were studied in primary schoolboys (6–10 years) infected with Ascaris lumbricoides (86%) and Trichuris trichiura (100%) who received a single dose of pyrantel pamoate (which has little or no effect on Trichuris trichiura ) or a placebo. Boys were examined, allocated at random by descending Ascaris egg count to pyrantel (PR, n = 36) or placebo (PL, n = 36) groups, treated, and re-examined 3 and 7 weeks later. The 2 groups did not differ significantly before treatment in helminth infections, appetite, or growth. Three and 7 weeks after treatment, the PR group exhibited significantly greater increases than did the PL group in weight (0·2 kg and 0·4 kg more, respectively) and percentage weight-for-age (0·6% and 1·7% points more, respectively). Appetite increased significantly in the PR group at 3 and 7 weeks (P < 0·0005 and P < 0·01, respectively) but not in the PL group. The prevalence and intensity of A. lumbricoides infection were greatly reduced in the PR group at 3 and 7 weeks (both P < 0·0001) but not in the PL group. We conclude that treatment with pyrantel pamoate may improve appetite and growth in schoolchildren in areas where A. lumbricoides infections and poor growth are highly prevalent.

Plasma membrane vesicles prepared from the bag region of the somatic muscle cells of the parasitic nematode Ascaris suum contain high conductance, voltage sensitive, Ca-dependent chloride channels, suggested to be involved in the excretion of carboxylic acids produced by the anaerobic respiration of glucose (Valkanov, Martin & Dixon, 1994). The effect of altered pH on this channel was investigated using the patch-clamp technique and isolated inside-out membrane patches. Changes in pH had little effect on channel conductances and only a small effect on reversal potentials. Under control conditions (symmetrical pH 7·2) the channel had the highest probability of opening at ∼ — 35 mV (the resting membrane potential of the cell). At positive membrane potentials the probability of opening decreased. The Boltzmann equation was used to describe the relationship between membrane potential and probability of channel opening, and to calculate the effective gating charge. Reduction of external pH produced an increase in the probability of channel opening at hyper-polarized membrane potentials. An increase in internal pH caused a voltage-independent increase in the probability of channel opening and made the effective gating charge less negative. The effect of reducing internal pH was marked: the channel then opened most frequently at positive membrane potentials and the probability of opening at —35 mV was greatly reduced. The decrease in internal pH changed the polarity of the effective gating charge. A simple model was constructed to describe the effects of pH on channel gating.

Heligmosomoides polygyrus is a gastrointestinal nematode whose adult distribution is restricted to the duodenal region in the small intestine of the mouse. This study tests the hypothesis that the habitat of these parasitic worms is influenced by fixed (architectural) cues in the small intestine of the vertebrate host, and that H. polygyrus adults will select microhabitats containing the longest villi. H. polygyrus adults attach by coiling around the villi, and longer villi may provide greater attachment resources. In addition, these parasites feed on the epithelial cells covering the villi and thus longer villi may also provide more food resources. Using histological methods, this study identified a gradient of villus length in the small intestine of the mouse where the longest villi were found in the duodenum and shortest in the ileum Several non-surgical and surgical treatments were used to differentially alter the overall lengths of the villi. These treatments produced a significant negative correlation between villus length and worm distribution, with the worms selecting regions with the relatively longest villi in the small intestine. Attachment and feeding sites are crucial resources for this parasite, and these data suggest that villus length may be a reliable indicator of resource quality, and that decisions on habitat suitability by H. polygyrus adults may depend on this single, topological variable.

Secretions of plant-parasitic nematodes which are released into plant tissue may play critical roles in plant-nematode interactions. The identification and characterization of these molecules are of fundamental importance and may help to facilitate the development of novel strategies to interfere with nematode infection of plants and thereby decrease nematode-induced damage to crops. An antibody-based approach was used to isolate molecules present on the nematode surface and in nematode secretions. Monoclonal antibodies (MAbs) were produced to secretions and to whole Heterodera avenue 2nd-stage juveniles; several of these MAbs recognized molecules present in nematode secretions produced in vitro. Three of these molecules have been partly characterized in H. avenae, Globodera rostochiensis, G. pallida and Meloidogyne incognita. A MAb reacting with the surfaces of these nematodes recognized antigens of different molecular weight in each of the species tested. This difference in antigenicity might be related to specific functions in these nematodes. Preliminary results show that this antibody also localized the antigen in root cells surrounding the feeding site induced by M. incognita in Arabidopsis thaliana.

The free living nematode, C. elegans is understood at a level of detail equalled by few other organisms, and much of the cell biology and sequence information is proving of considerable utility in the study of parasitic nematodes. Already, C. elegans provides a convenient vehicle for investigating anthelmintic drug action and resistance mechanisms. Among the ionotropic receptors, with their important roles in the behaviour and development of the organism, are targets for anthelmintics. The subunits of nicotinic acetylcholine receptors of C. elegans form a large and diverse multigene family. Members of this family are among the 11 genes associated with resistance to the anthelmintic drug levamisole.

We analysed the patterns of tick distribution on 2274 adult toads from Venezuela and Brazil, to explore whether these ectoparasites have any impact on the survival of Bufo marinus. A maximum-likelihood analysis showed that aggregation levels of ticks decreased significantly with the mean intensity of infection. This decline could be attributed to a density-dependent reduction of ticks within toads, density-dependent tick-induced toad mortality and/or density-dependent tick-induced changes in toad susceptibility. However, the relationship between the rate of change in tick loads and tick burdens from recaptured toads indicated that neither the loss of ticks within toads nor the toad susceptibility to further infection were dependent upon tick burdens. Therefore, we can indirectly infer that density-dependent tick-induced toad mortality is responsible for the observed decline in aggregation levels with tick age and burdens. On the other hand, a significant negative relationship between tick burdens and the size-specific weight of toads suggested that ticks may also have a significant impact on the patterns of weight deposition of adult toads. This evidence suggests that these ectoparasites may play an important role in regulating the densities of B. marinus in native habitats.