In this study we evaluated the effects of the anti-microsporidial exospore monoclonal antibody 3B6, recognizing 3 Encephalitozoon species, Encephalitozoon intestinalis (Syn. Septata intestinalis), Encephalitozoon cuniculi, and Encephalitozoon hellem on microsporidial growth in vitro. Pre-treatment of spores for 24 h with mAb 3B6 resulted in 21–29% fewer infected host cells 4 days after inoculation of the cultures compared to cultures pre-treated with medium or an irrelevant isotype control mAb (P<0·001). Fewer intracellular spores (1·2±0·2) in infected cells were found when mAb 3B6 was present in cultures compared to cultures with medium alone (4·3±0·8) or an irrelevant isotype control mAb (4·2±0·9; P<0·001). This decrease appeared not to be dependent on time of exposure, mAb concentration, or presence of complement. It is concluded that antibodies, particularly those directed to potential neutralizing-sensitive epitopes on spores, may have a role in the control of microsporidial growth in vitro.

We have investigated the influence of heteroxenous coccidia (Apicomplexa: Eimeriorina) on the predation risk of intermediate hosts. Voles infected with Frenkelia spp. were found more frequently in buzzards' (Buteo buteo) prey than among snap-trapped rodents. To eliminate the possibility of traps selecting for uninfected rodents, a laboratory experiment was performed. Mice experimentally infected with Sarcocystis dispersa seemed to be more likely caught by the final host, the long-eared owl (Asio otus); this result was confirmed by a mathematical model. Field data confirmed the adaptive value of parasite-induced changes. The increase of predation is directed towards the specific final host only or is non-specific. In the populations studied the probability of predation of parasitized individuals by the specific predator was increased.

Severe cryptosporidial infections were produced in gamma interferon (IFN-γ) knockout mice. Mean oocyst shedding increased from 332 to 30717 oocysts/100 μl of faecal suspension between day 4 and 9 after administration of 1×105 oocysts/mouse. No significant differences in oocyst shedding were observed in mice after being inoculated with 1×105, 1×104 or 1×103 oocysts/mouse (P>0·05). Infected mouse weights decreased an average 3–4 g before death or euthanization. Histological studies revealed heavy parasite colonization in small intestinal epithelium (approximately 250 organisms/high-power field at ×400). Mesenteric lymph nodes in infected mice were markedly enlarged compared to controls (P<0·05). Both CD4+ and CD8+ T cell populations increased in spleens of infected mice while the B cell population increased in mesenteric lymph nodes from infected mice. No significant proliferation was observed when pooled lymphocytes from infected mice were exposed to C. parvum antigens in vitro. Addition of recombinant mouse IFN-γ did not restore antigen responsiveness. While lymphoproliferative responses to specific antigen were not significant in the short period following infection, this mouse model provides unique features to study the characteristics of acute infection and the immune response against C. parvum.

Binding of Plasmodium falciparum-infected erythrocytes (PE) to endothelial cells is mediated by the erythrocyte-membrane protein, band 3-related adhesin. To determine its role, the binding of infected cells treated with various chemical modifiers was investigated. Binding was inhibited by a lysine modifier (4,4′-diisothiocyanostilbene-2,2′-di-sulfonate (DIDS)) known to specifically bind to band 3, another lysine modifier (trinitrobenzene sulfonic acid), a tyrosine modifier (sodium iodide in conjunction with lactoperoxidase, hydrogen peroxide) and oxidants (diamide, sodium periodate and ADP-chelated ferric ion), but binding was unaffected by the histidine modifier (diethylpyrocarbonate) and the arginine modifier (phenyl glyoxyl monohydrate). To artificially expose the band 3-related adhesin, uninfected erythrocytes were treated with acridine orange or loaded with calcium. These cells bound to C32 amelanotic melanoma cells, were immunostained with a monoclonal antibody that specifically binds to the band 3-related adhesin on PE, and the binding was inhibited by this monoclonal antibody. The binding of acridine orange-treated and calcium-loaded uninfected erythrocytes, could also be blocked by DIDS. In the case of acridine orange-treated erythrocytes, the patterns of the effects of the chemical modification on binding were consistent with that of PE except for tyrosine modification. These results demonstrate that the band 3-related adhesin, even in the absence of parasite-encoded proteins, contributes to PE adhesion.

The in vitro activity of artemether against 63 African isolates of Plasmodium falciparum from Libreville, Gabon was evaluated using an isotopic drug susceptibility semi-microtest. The 50% inhibitory concentration (IC50) values for artemether were in a narrow range from 0·8 to 34·8 nm (mean IC50 5·0 nm) and the 95% confidence interval (CI95%) was 3·6–6·3 nm. In vitro decreased susceptibility or resistance were observed with artemether (14%), to chloroquine (90%), to quinine (32%). Isolate susceptibility to amodiaquine and halofantrine was high i.e. 100% and 98%, respectively. There was a significant positive correlation between responses to artemether and amodiaquine (r2=0·45, P<0·001), artemether and chloroquine (r2=0·36, P<0·001), artemether and quinine (r2=0·31, P<0·001), and artemether and halofantrine r2=0·19, P<0·01). Positive correlation between these drugs suggests in vitro cross-resistance or at least common features in drug uptake and/or mode of action or resistance.

Five chromosomes and 17 isoenzyme loci were analysed in 4 allopatric populations of Leishmania (Viannia) peruviana, and molecular distances calculated with 2 estimators, Chromosomal Size Difference Index and Jaccard Distance. Chromosome and isoenzyme data were in overall concordance: 13/30 isolates clustered similarly on the dendrograms constructed from the different estimators, and a significant correlation (P<0·001) was observed between the molecular distances calculated from the two sets of characters. This indicates an evolutionary association between chromosomal size polymorphism and isoenzymes. Chromosomes have a faster molecular clock than isoenzymes; twice as many genotypes were identified by chromosome analysis and significant size differences (for a total of up to 500 kb for 5 chromosomes together) were observed within a given zymodeme. Chromosomes most likely represent better indicators of genetic drift than isoenzymes, as suggested by the higher correlation between both estimators of chromosomal size-polymorphism and eco-geography. Some chromosomes might present an adaptive response to environmental variation.

The levels of superoxide dismutase (SOD) were determined in detergent-soluble, somatic and excretion–secretion (E–S) preparations from adult Fasciola hepatica using the xanthine oxidase system and visualized in substrate gels. Compared to detergent-soluble and somatic extracts, E–S products showed the highest SOD activity (88 ·5 U/mg), indicating active release to the medium in which parasites were maintained. SOD specific activity was also detected at high levels in E–S products from 3-week-old and 5-week-old immature migrating flukes (25 and 143 U/mg, respectively). In all preparations except for the somatic extract, the activity was characterized as cyanide-sensitive CuZn SOD. Differences in SOD isoenzyme profiles between the extracts were observed in native polyacrylamide gel electrophoresis: the somatic and detergent-soluble extracts exhibited 1 band of activity while the E–S products from immature and adults flukes contained 2 and 3 migrating bands, respectively. SOD was purified from the detergent-soluble extract and E–S products of adult worms by a combination of ultrafiltration, gel filtration on Sephacryl S-200 HR and ion-exchange chromatography on QAE Sephadex A-50. The SOD from detergent-soluble extract showed, by SDS–PAGE analysis, 1 band of 16 kDa apparent molecular weight. The SOD from E–S products showed 2 bands of 16 and 60 kDa apparent molecular weight. N-terminal sequence analysis of the 16 kDa band from the detergent-soluble preparation showed some similarity with Schistosoma mansoni cytoplasmic SOD. These enzymes may have a potential role in the evasion of the oxidative burst killing mechanism by immune cells.

Adults of the monogenean genus Protopolystoma infecting Xenopus species occur in an extremely space-limited habitat, the urinary bladder. Xenopus wittei, from a population in Rwanda naturally infected with Protopolystoma fissilis and Protopolystoma simplicis, were exposed to reinfection in captivity (for 1–3 months post-capture) and then monitored in the laboratory for up to 5 months in transmission-free conditions. The two parasites co-occurred in individual bladders less frequently than expected if they were dispersed randomly. Distribution of bladder infections was significantly non-independent (n=157) and gravid worms of both species were never found in the same host. This pattern might be explained by interference competition between the parasites or by genetic differences in susceptibility within the host species, which is of allopolyploid origin. Other distributional data for sympatric polystomatid species pairs, including P. fissilis and P. ramulosus, show concurrent infections at frequencies consistent with random distributions (i.e. no evidence of interspecific competition or variability in species-specific susceptibility of the hosts). Interference between P. fissilis and P. simplicis (assuming host genetic factors are not involved) may therefore result from a mechanism specific to this species pair. Observations on infection turnover in captive hosts suggest that loss of adult worms may be related to the arrival of juveniles (of either species) in the urinary bladder. Ectopic infection of the host urinary ducts by adult and subadult P. fissilis was observed in some single-species infestations and may be density related. However, the use of an ectopic-site ‘refugium’ has never been observed in concurrent polystomatid infections.

We compared, some fitness-related traits of benzimidazole resistant (rr) and susceptible (rS, SS) worms of Teladorsagia circumcincta, a gastrointestinal parasite of the small ruminants, under laboratory conditions. PCR was used to determine the genotypes (rr, SS, rS) and the fitness of each was compared within the same strain. There was no significant difference in egg production, development rate from egg to infective larvae stage, establishment of these larvae in the host or the survival of adult worms and infective larvae for the 3 genotypes. The same results were obtained for the establishment rate of larvae in the host and the production of infective larvae under conditions of strong competition between resistant and susceptible worms. The fact that there were no differences in fitness suggests that the installation of benzimidazole resistance in a worm population is irreversible. This agrees with field observations.

Tapeworms absorb and consume large quantities of glucose through their syncytial tegument, storing the excess as glycogen. Although some studies on the metabolism of glucose in several tapeworms are available, the proteins that mediate its uptake and distribution in their tissue have not been identified. We describe the isolation and characterization of cDNA clones encoding 2 facilitated diffusion glucose transporters (TGTP1 and TGTP2) from Taenia solium, the causal agent of human and porcine cysticercosis. Radio-isotope labelled hexose uptake mediated by TGTP1 expressed in Xenopus oocytes is inhibited by the natural stereoisomers d-glucose and d-mannose but not by l-glucose. Transport by TGTP1 is sensitive to classical inhibitors of facilitated diffusion such as phloretin and cytochalasin B, and insensitive to ouabain. TGTP2 did not function in Xenopus oocytes. Localization studies using specific anti-TGTP1 and anti-TGTP2 antibodies show that TGTP1 is abundant in a number of structures underlying the tegument in adult parasites and larvae, whereas TGTP2 appears to be localized only on the tegumentary surface of the larvae and is not detected in adults.

This paper describes the distribution of Ascaris suum in experimentally and naturally infected pigs, and offers a comparison with A. lumbricoides infections in humans. In the first study, worms were recovered post-mortem from a group of 38 pigs that had been trickle inoculated with 10000 infective A. suum eggs twice weekly for 12 weeks. In the second study, worms were collected from a group of 49 pigs that had been kept on a pasture contaminated with infective A. suum eggs for 10 weeks, after which they received treatment with an anthelmintic; they then were turned out on the same pasture for a second 10-week period before slaughter. The worm burdens of the naturally infected pigs were recorded both at treatment and post-mortem. Mean worm counts were similar at all occasions but the prevalence of infection was higher in the trickle infected and naturally reinfected pigs. Furthermore, the prevalence in naturally infected pigs increased significantly over the study period. Worm burden distributions in all groups were heavily overdispersed, but the distribution patterns differed significantly between groups: lower exposure (initial natural infection) gave a low prevalence and an almost uniform distribution of worm burdens among infected hosts. Continued or higher exposure (trickle and natural reinfection) resulted in increased prevalence and a reduction in the proportion of hosts with increasing worm load. A positive correlation was found between initial and reinfection worm burdens in the naturally infected pig population, suggesting that individual pigs are predisposed to a high or low intensity of infection. The prevalence and intensity as well as the distribution observed for A. suum infection in pigs were comparable to those reported for A. lumbricoides in endemic areas, and there is evidence for predisposition to A. suum in pigs, with an estimated correlation coefficient similar to that found in humans. It is concluded that A. suum infections in pigs are a suitable model to study the population dynamics of A. lumbricoides in human populations.

Frequency distributions from 49 published wildlife host–macroparasite systems were analysed by maximum likelihood for goodness of fit to the negative binomial distribution. In 45 of the 49 (90%) data-sets, the negative binomial distribution provided a statistically satisfactory fit. In the other 4 data-sets the negative binomial distribution still provided a better fit than the Poisson distribution, and only 1 of the data-sets fitted the Poisson distribution. The degree of aggregation was large, with 43 of the 49 data-sets having an estimated k of less than 1. From these 49 data-sets, 22 subsets of host data were available (i.e. host data could be divided by either host sex, age, where or when hosts were sampled). In 11 of these 22 subsets there was significant variation in the degree of aggregation between host subsets of the same host–parasite system. A common k estimate was always larger than that obtained with all the host data considered together. These results indicate that lumping host data can hide important variations in aggregation between hosts and can exaggerate the true degree of aggregation. Wherever possible common k estimates should be used to estimate the degree of aggregation. In addition, significant differences in the degree of aggregation between subgroups of host data, were generally associated with significant differences in both mean parasite burdens and the prevalence of infection.