Isolates of Trypanosoma cruzi from human patients, domestic and sylvatic animals and vector insects were obtained in different areas of Argentina. Electrophoretic patterns of enzymes from extracts of 95 isolates were analysed. On the basis of zymograms providing information on 10 loci, 12 zymodemes are described according to their genotypes. Data presented show fixed heterozygosity, absence of segregation of genotypes, significant departures from Hardy–Weinberg equilibrium, and over-represented genotypes. This evidence supports the hypothesis that sexual reproduction is very restricted or absent in this parasite. The proportion of polymorphic loci is 80%. The expected mean heterozygosity per locus (He) is 0·43, while the observed value (Ho) is 0·24. Differences between these values may be explained by accepting a basically clonal structure for T. cruzi. The data matrix of 12 zymodemes using 28 characters was analysed using a Wagner parsimony algorithm. Two equally most parsimonious unrooted trees were generated; both have 39 steps. The results show clusters clearly separated according to the geographical origin of the stocks. There are some indications of some correlations between genetic composition of the parasite and the clinical picture of the infection in human patients.

Megatrypanum trypanosomes have been isolated from a number of different European Cervidae, but on the basis of morphology it has not been possible to define the species to which these isolates belong. We isolated Trypanosoma (Megatrypanum) theileri from 10 cattle, and Megatrypanum trypanosomes from 11 fallow deer (Cervus dama), 9 red deer (Cervus elaphus), and 4 roe deer (Capreolus capreolus) by blood culture on a biphasic medium (NNN agar slopes). Trypanosomes were propagated in Schneider's Drosophila medium and characterized by isoenzyme analysis and molecular karyotyping. Isocitrate dehydrogenase and phosphoglucomutase were visualized after starch gel electrophoresis of trypanosome lysates. By cluster analysis of this data all isolates from deer were clearly separated from the T. (M.) theileri isolates from cattle. Isolates from roe deer were different not only from T. (M.) theileri but also from the other deer isolates. Isolates from fallow deer and red deer were grouped together. Thus, there are probably at least two different species of Megatrypanum trypanosomes in the three Cervidae. One parasitizing roe deer, the other, apparently less host specific species, infecting red deer and fallow deer. Separation of the chromosomes of Megatrypanum trypanosomes by pulsed-field gradient gel electrophoresis (PFGE) showed that each isolate contained a large number (> 18) of chromosomes ranging in size from 300 to > 2200 kb. The molecular karyotypes were similar for all isolates, although no isolate was identical to another.

A murine AIDS model with many similarities to human AIDS, LP-BM5 Murine Leukaemia, suppresses T and B cell numbers and functions in the intestine. This permits chronic colonization by Giardia and Cryptosporidium. Cocaine and the nutrient alcohol, which are immunosuppressive, further reduce resistance to intestinal parasites and intestinal lymphocyte numbers. Protein undernutrition, vitamin E supplementation, and alcohol use further modify immune dysfunction induced by the murine retrovirus infection. This suggests that both undernutrition and nutrient supplementation could affect parasite resistance during AIDS. Thus this murine model of human AIDS has great potential to accelerate studies of the role of nutrients in immune dysfunction and resistance to intestinal parasites.

The use of a selective schedule of tests to identify a viable population of isolated adult Onchocerca volvulus (Nematoda: Filarioidea) has been investigated in a large worm population. The study was initiated to develop methodology appropriate to test new candidate macrofilaricides for their in vitro activity against O. volvulus. After removal from the host the viability of isolated intact parasites was estimated by assessing the motility indices of male worms, and the colorimetric quantification of the reduction of the bioreducible tetrazolium reagent XTT and lactate output by female worms. Additionally the motility of whole females and the movement of inner organs of female worms were scored quantitatively. These response parameters were used to sort the adult worms into viability groups at the start of the in vitro culture. The adult worms were then observed for 6 days and viability was assessed regularly during the culture period. At the end of the culture period, the reduction of the water-insoluble tetrazolium reagent MTT was used to determine the formazan formed by the entire male and female worms. The response parameters used at the start of the culture proved to be highly predictive for detecting viable and non-viable adult worms. In the group of worms selected as ‘viable’ around 70% kept their motility and metabolic activity at a high level until the end of the culture compared to the initial level. In contrast, none of the female worms and only 13% of the male worms categorized as ‘poorly viable’ demonstrated a motility index or metabolic level at the end of the culture period that was comparable to that of the worms in the ‘viable’ groups. For female worms the lactate output correlated significantly with weight whereas no correlation was seen between MTT reduction and weight.

We exposed 19 species of cockroaches to Moniliformis moniliformis by administering shelled acanthors orally and by injecting hatched acanthors directly into the body cavity. The exposure method had little influence on susceptibility: with one exception, species that were susceptible to oral exposure were also susceptible to injected acanthors and, in no case, did acanthors develop in injected animals when they did not develop in orally exposed conspecifics. We found no support for the hypothesis that the intestine may be a barrier to M. maniliformis establishment in cockroaches. There is, however, clear interspecific variation in susceptibility to M. moniliformis infection.

Infection by Schistosoma mansoni resulted in morphological and biochemical changes to the foot of its intermediate host, Biomphalaria glabrata. Migration through, and emergence of cercariae from, the foot was observed and evidenced by lesions on the ciliated foot surface. This was accompanied by a significant decrease in the velocity of movement by infected individuals. In vivo31P NMR spectral analyses demonstrated that the foot of infected snails had a lower phosphoarginine (PA)/adenosine 5' triphosphate (ATP) ratio than that of uninfected controls. Moreover, kinetic experiments, employing saturation transfer, demonstrated the pseudo-first-order rate constant for the arginine kinase-catalysed exchange reaction in the forward direction, that is, PA→ATP was decreased by infection. The reverse reaction was not observed by the NMR methods used. PA was depleted upon exposure to hypoxic conditions suggesting its traditional role in preserving ATP level. Partly oxidized metabolic end-products were not observed in snails maintained under aerobic conditions, but succinate, propionate, acetate and lactate rapidly accumulated under hypoxic conditions.

Serum from uninfected mice of different strains, as well as from germ-free animals, contains antibodies which react specifically with at least two trypanosomal proteins, I/6 and MARP1. These antibody populations are highly specific for the respective proteins, are of similar affinity as hyperimmune antibodies, and consist of IgM as well as IgG isotypes. Hyperimmune antibody raised against the cross-reacting trypanosomal protein I/6 detects a 60 kDa protein in mouse 3T6 cells, which is a component of the fibroblast cytoskeleton.

The entire ribosomal DNA repeat unit of a steinernematid species (Nashes isolate) was cloned as three separate EcoR I fragments in the plasmid pUC18. An equimolar cocktail of these three clones was used to identify Steinernema species on Southern blots as each species displays its own unique restriction fragment length polymorphisms. The clones also identified two new species isolated in a soil survey of coastal regions of Britain. One of the clones (pSn4.0) can detect length heterogeneities in the rDNA repeat unit of various isolates of some of the species, particularly the most common in the United Kingdom, S. feltiae. These differences in the rDNA repeat unit length remained constant over several years for one isolate of S. feltiae, but were different for each of the geographical isolates studied to date.

The prediction that species richness and diversity of intestinal helminth communities in eels would change over time in response to habitat changes was tested over a period of 13 years in a small stream subjected to extensive human management. Nearly all measures of helminth community structure adopted indicated a decline in richness and diversity over the first 6 years followed by a recovery over the last few years to levels unexpectedly close to those at the start of the investigation. Changes in total number of species suggested that the component community was far richer (from 3–9 species) at the end of the period. By contrast, changes in diversity and dominance measures revealed less variation than expected and suggested that there was an underlying stability of community structure characterized by high dominance by a single species, although the identity of this changed, low diversity and a large proportion of the eel population harbouring 0 or only 1 species. A similar pattern of changes was recorded in the infra-communities, where values of species richness and diversity were very similar at the commencement and termination of the study. It appeared that those helminths that colonized in the recovery period contributed to community richness but had little impact on community structure. The helminth communities clearly did change in response to habitat changes, and the evidence for a fixed number of niches and an underlying constancy in helminth community structure in eels is evaluated.

The number of episodes of diseases caused by bacterial contamination of food has shown a real increase by about threefold in the last decade in the U.K. The numbers for 1992 are estimated to be 2 million. The causes are multifactorial and complex, and 4 representative pathogens are reviewed. The main increase in diseases due to salmonella has been caused by Salmonella enteritidis, especially from eggs. The commonest bacterial food pathogen is Campylobacter, which causes an illness with specific season peaks in May and June. This may be related to the activities of birds and mammals. Both these bacteria cause common diseases that are rarely fatal. In contrast, Listeria and E. coli are ubiquitous but rarely produce disease; however, the consequences of any such illness are often dire. Procedures and techniques are available for the control of most of these diseases, but society does not seem determined to implement them.

For the description of the dynamics of snail infection by the 1st-stage larvae of protostrongylid nematodes, Skorping (1988) used the miracidia-snail model (Anderson, 1978). Here it is shown that, in contrast to miracidia, in protostrongylids the instantaneous rate of infection, α, is strongly dependent on the experimental design (factors like host size and size of the experimental arena). With respect to this, Anderson's model is modified by incorporation of the experimental design. The parameter α in its new sense as the rate of penetration (probability that the infective larva will penetrate into the host during a time unit) is shown to remain dependent, although much less so, on the experimental design. Only the inclusion of the assumed effect of mucus, which decreases the rate of penetration, yields a parameter α0 (the initial rate of penetration), which is completely independent of the design of the experiment, is species-specific, and also gives the best fit to the empirical data. As the above-mentioned factors can strongly influence the value of the instantaneous rate of infection in the laboratory experiments, α0 is more suitable as a measure of either the larval infectivity for the snail or snail susceptibility to infection by the protostrongylid larvae.

An earlier paper (May, 1977) developed a theoretical framework for exploring the consequences of dioecy for the population dynamics of schistosomes, assuming an unbiased sex ratio. This paper extends the analysis to biased sex ratios, as have been reported in practice. We consider the relationships of the mean number and distribution of worms among hosts, the sex ratio, and the mating system (monogamous or polygamous) to: (i) the female mating probability, Φ the prevalence of mated female worms. Ω: and (iii) the mean number of mated female worms per host, ξ. Among other results, we show how high values of Φ are associated with male-biased sex ratios and polygamous mating; that Ω is independent of the mating system and is relatively unaffected by the sex ratio; and that ξ is maximal for unbiased sex ratios given monogamous mating, and for female-biased sex ratios if mating is polygamous. These results, together with the confounding effects of the mean number and distribution of worms, are described in detail in the main body of the paper.

The random amplified polymorphic DNA (RAPD) technique was successfully used to produce genetic fingerprints distinguishing between Trichinella spiralis and Trichinella britovi. The same patterns were obtained from purified and crude DNA preparations of pooled and single muscle larvae. RAPD fingerprinting was applied to muscle larvae preserved under different conditions and recovered from different hosts. Larvae recovered from fresh and frozen meat and stored at – 20 °C for a long time or under 70% ethyl alcohol at room temperature for 30 d gave good and reproducible results. Single larvae recovered from a naturally infected wild boar and from a human biopsy gave fingerprints congruent to those obtained from T. britovi reference strains. The results prove that RAPD analysis is a quick method to distinguish between the autochthonous Trichinella species of Central-Southern Europe in less than 1 d after the detection of the infection. If necessary, the biological material can be frozen or stored under 70% ethyl alcohol at room temperature and sent to laboratories able to perform the RAPD analysis. The RAPD technique requires no prior knowledge of the molecular biology of the organism to be investigated and therefore appears to be a promising tool in parasitology for the identification of sibling species.

Unrelated and initially unfamiliar male CFLP mice, maintained for different periods in groups of 6, differed in both their rate of clearance of Babesia microti and the time taken to reach peak parasitaemia in relation to their aggressive behaviour within groups prior to infection. Males maintained in groups for shorter periods and showing more aggression within their group were slower to clear infection and males showing more marked external evidence of aggressive interaction reached a peak of parasitaemia sooner. Serum IgG and corticosterone analyses were consistent with increased aggression causing stress-induced immunodepression but relationships with aggression and social status were not simple. Males showing more aggression tended to enter their groups with higher levels of corticosterone and, to a lesser extent, reduced levels of IgG compared with other mice. The results thus suggest that increased susceptibility to disease may be a cost to males aggressively maintaining high social status.

Susceptibility to oxidative stress is a well-established feature of the malarial parasite. Pharmacologists have taken advantage of this property to design highly effective pro-oxidant antimalarial drugs. Less well appreciated is the fact that nutritional manipulation of host oxidative stress status by dietary means can have a profound effect on the growth of the parasite. In particular, rapid induction of vitamin E deficiency in mice by feeding highly unsaturated fatty acids (fish oil) strongly suppresses plasmodial growth. Likewise, the status of other antioxidant nutrients (e.g., riboflavin or vitamin C) may also influence the course of malarial infection under certain conditions. A combined nutritional pharmacology approach may offer some promise in controlling malaria.

Comparisons were made between the protein concentrations and protein profiles of uninfected Gammarus pulex and those infected with cystacanths of Pomphorhynchus laevis. Comparisons of the extractable haemolymph volumes from uninfected and infected G. pulex, when related to host tissue weight, showed that there was no difference in the host tissue/haemolymph volume ratio between infected and uninfected individuals. SDS-PAGE of haemolymph samples resolved 36 bands of protein, the major components being band 6(19 kDa) and 21(33 kDa). Densitometric analysis of haemolymph samples showed that infected gammarids had total protein concentrations elevated by 84%. The (88 kDa) subunit was identified as the monomer of the respiratory protein haemocyanin. This band was significantly elevated in infected individuals (one-way ANOVA P < 0.001); increasing from 30 to 45% of the total haemolymph proteins.

The surface of the cuticle of adult Nippostrongylus brasiliensis has been studied by means of the freeze-fracture technique and by transmission electron microscopy. Some of the surface coat appears to have been shed from the surface of the cuticle of adults fixed in situ in the intestine of its host and from the surface of individuals removed from the intestine and freeze-fractured. Freeze-fracturing the cuticle of individuals removed from the host has shown that this surface coat varies in thickness from 30 to 90 nm. The epicuticle is about 20 nm thick and cleaves readily to expose E- and P-faces. The P-face of the epicuticle possesses a small number of particles, similar to intra-membranous particles, whilst the E-face possesses a few, widely scattered depressions. Despite the presence of these particles the epicuticle is not considered to be a true membrane. Freeze-fracturing the remainder of the cuticle has confirmed its structure as described by conventional transmission electron microscopy. Clusters of particles on the P-face of the outer epidermal (hypodermal) membrane and corresponding depressions on the E-face of the membrane are thought to be associated with points of attachment of the cuticle to the epidermis (hypodermis). No differences in appearance of the cuticle and its surface layers were observed in individuals taken from 7-, 10-, 13- and 15-day infections.

A dipstick dot ELISA for detection of Taenia-specific coproantigens was developed. The test was based on a sandwich ELISA using antibodies raised against adult Taenia solium. Antibodies were adsorbed to nitrocellulose paper previously adhered to acetate plastic to form dipsticks. Once blocked with 5% skimmed milk and dried the antibody-coated dipsticks were stable for several weeks at room temperature. Both micro and dot ELISA formats were genus specific although the dot ELISA was less sensitive than the micro ELISA based on the same antiserum. During field studies, in which the majority of samples were tested in rural villages soon after collection, 3728 samples were tested. All samples were also examined by microscopy using formol ether concentration and individuals questioned to determine whether they were aware of being infected. After the initial diagnostic work individuals were treated with taeniacidal drugs for worm recovery. Use of the coproantigen test significantly increased the number of cases diagnosed. Of the 41 cases diagnosed by the three diagnostic techniques combined 31 were detected by the dipstick assay making it the most sensitive technique employed. The specificity of the dipstick assay was 99·9% with a positive predictive value of 88·%. The combined diagnostic approach did not, however, diagnose all cases. The coproantigen test was fast and easy to use. Further improvements may make the dipstick test suitable for wide-scale use in field studies and diagnostic laboratories.

The course of a primary Necator americanus infection was studied in the lungs and small intestines of syngeneic mice. Following percutaneous infection no difference in initial larval establishment in the lungs was found between male BALB/c, NIH or B10.G mice. However, significant differences in the subsequent kinetics of infection were demonstrated between the BALB/c and NIH strains. Lung worm burdens declined more slowly in NIH mice than in BALB/c strain. Surprisingly, however, a greater proportion of larvae remaining in the lungs of BALB/c mice, 9 days p.i., were trapped than in NIH mice. Nevertheless, establishment in the small intestines of the BALB/c strain was consistently greater than in NIH mice. Host immunosuppression resulted in increased larval retention in the lungs of both the BALB/c and NIH strains as well as in the small intestines of BALB/c mice. Treatment with hydrocortisone acetate did not increase intestinal worm burdens in NIH mice. The data presented suggest that, in this complex, dynamic model system, designation of ‘susceptible’ and ‘resistant’ strains is inappropriate. The factors underlying the observed strain differences in resistance to infection are discussed.

The effect of the microtubule inhibitors coichicine (1×10−3 M) and tubulozole-C(1×10−6 M) on the ultrastructure of adult Fasciola hepatica has been determined in vitro by transmission electron microscopy (TEM), using both intact flukes and tissue-slice material. With colchicine treatment, the apical membrane of the tegument became increasingly convoluted and blebbed, while accumulations of T1 secretory bodies occurred in the basal region of the syncytium, leading to progressively fewer secretory bodies in the syncytium. In the tegumental cells there were distinct accumulations of T1 secretory bodies around the Golgi complexes, which remained active for up to 12 h incubation. Tubulozole-treated flukes showed more severe effects, with initial accumulations of secretory bodies, both at the tegumental apex and base. This was followed in the later time-periods by the sloughing of the tegumental syncytium. In the underlying tegumental cells, the granular endoplasmic reticulum (GER) cisternae were swollen and disrupted, becoming concentrated around the nucleus. The Golgi complexes were dispersed to the periphery of the cells and gradually disappeared from the cytoplasm. After treatment with both drugs, the cell population in the vitelline follicles was altered, with an abnormally large proportion of stem cells and relatively few intermediate type I cells. The nurse cell cytoplasm became fragmented and was no longer in contact with the vitelline cells, while the shell globule clusters within the intermediate type 2 and mature cells were loosely packed. In the mature vitelline cells, ‘yolk’ globules and glycogen deposits became fewer than normal and lipid droplets were observed. The results are discussed in relation to the different modes of action of the two drugs and potential significance of this to anthelmintic (benzimidazole) therapy.