The present study followed a Plasmodium falciparum population through its life-cycle at the level of individual hosts and vectors. The aim was to determine to what extent genotypes of the parasite that were found in the host were transmitted to the vector. Mosquitoes were collected that had fed on people sleeping under mosquito nets with holes. Genes determining 2 highly polymorphic merozoite surface proteins, MSP-1 and MSP-2, were used to characterize the parasite by PCR at different stages of the life-cycle. The parasite genotypes found in the host were compared to the genotypes of the oocyst stages after transmission to the mosquitoes. The results show that there was no significant correlation in the rate of oocyst-positive mosquitoes and the presence of parasites in the blood samples. For MSP-1, most of the parasites characterized in the human blood by PCR fragment size were also found afterwards in the oocyst-stage (22 of 29; MSP-2: 17 of 36). This study indicates that there is no selective transmission of distinct genotypes to the vector. In addition, the frequencies of the allelic families of both genes are similar in the blood samples and in the oocysts for the whole population.

Leishmania braziliensis strain M2903 was adapted for growth and serially maintained as amastigotes at 34°C in modified UM-54 medium, with growth curves exhibiting typical log and stationary phases. In late passages, amastigote growth took place in the absence of supplementary haemin and was unaffected when the initial medium pH was adjusted between 5·4 and 6·3. In contrast to promastigotes, which were elongated and exhibited very long free flagella endowed with the paraflagellar rod (PFR), axenic amastigotes were rounded to ovoid and displayed a short flagellum restricted to the pocket area. The absence of PFR in axenic amastigotes was confirmed in Western blots and confocal immunofluorescence microscopy, by lack of reactivity with mAb 1B10. The antibody, which specifically labelled the paraflagellar structure, recognized a 70/72 kDa doublet in Trypanosoma cruzi epimastigotes and two 70/74 kDa related proteins in L. braziliensis promastigotes. Surface 125I-labelling experiments identified promastigote-specific components (>100, 74, 45/47 and 28 kDa) and at least 1, a 76 kDa polypeptide was specific for the amastigote stage. While axenic amastigotes were agglutinated by both peanut (PNA) and Lens culinaris (LCA) agglutinins, respectively at 50 and 12·5 μg/ml, promastigotes were not agglutinated by PNA and agglutinated in the presence of LCA at concentrations of 100 μg/ml and higher. Axenic amastigotes infected rat bone marrow-derived macrophages and were avidly taken up by J774 cells, from which numerous organisms, able to proliferate at 34°C in UM-54 medium, could be recovered 48 h later.

Dinoflagellates are common and often important parasites of aquatic organisms, but their developmental cycles are poorly known and have not been established in in vitro culture. The parasitic dinoflagellate (Hematodinium sp.) associated with mortality of the Norway lobster (Nephrops norvegicus) in British waters has been cultivated in vitro in 10% foetal calf serum in a balanced Nephrops saline. In culture the parasite undergoes a characteristic cycle of development. Circulating sporoblasts from the host's haemolymph in vitro generate 2 kinds of flagellated uninucleate dinospore, macrospores and microspores, either of which will, after 5 weeks in fresh medium, germinate to produce multinucleate unattached filamentous trophonts. These trophonts multiply by fragmentation and growth and may be serially subcultured in this form, at 2 week intervals, indefinitely. If not subcultured, the filamentous trophonts give rise to colonies of radiating filaments (‘gorgonlocks’) which subsequently attach to the substratum to form flattened web-like ‘arachnoid’ multi-nucleate trophonts. Arachnoid trophonts become arachnoid sporonts when they synthesize trichocysts and flagellar hairs and may give rise to secondary arachnoid sporonts or to dinospores which initiate a new cycle.

A female-specifically expressed cDNA clone was obtained by screening of a subtractive cDNA library enriched for RNA from Schistosoma mansoni females. The deduced protein shows significant homology to a class of enzymes functioning as amidases. Northern blots revealed a transcript of 4·0 kb which is absent in larval stages, but is expressed in adult female worms. By in situ hybridization, the expression site of the gene was exclusively localized in the gastrodermis of female schistosomes. This is the first report of a female-specifically transcribed sequence of S. mansoni that is not expressed in the reproductive organs.

Schistosome cercariae of the genus Trichobilharzia are the causative agent of swimmers' itch. In order to characterize the changes in parasites during and after the penetration of the host skin, in vitro and in vivo (in ducks and mice) transformations of T. szidati cercariae to schistosomula were performed. Ultrastructural observation revealed that cercariae possess a simple outer tegumental membrane with a thick glycocalyx. As with human schistosomes, the latter structure disappears during transformation and a new double membrane with putative protective function is formed. Our biochemical and immunological observations showed that the carbohydrate-rich glycocalyx of cercariae is readily bound by lectins and antibodies. The in vitro transformation to schistosomula can be detected by enhanced reactivity of 2 lectin probes (PNA and ConA) with the surface. The in vivo-transformed (skin and lung) schistosomula appear to have few surface ligands for the 12 lectin probes being tested. Similarly, the cercarial surface and its remnants on the in vitro-produced schistosomula is recognized by sera from immunized mice and humans with cercarial dermatitis; the tissue schistosomula fail to react with these antibodies. The loss of surface targets as a part of parasite immune evasion within the host is discussed.

Epidemiological models are used to analyse 8 published data sets reporting age–prevalence curves for trypanosome infections of the tsetse fly Glossina pallidipes. A model assuming a fixed maturation period and a rate of infection which is independent of fly age is adequate for Trypanosoma vivax-type infections, explaining 98% of observed variance in prevalence by site and age, allowing that the rate of infection may be site dependent. This model is not adequate for T. congolense-type infections and the fit can be improved by allowing (i) the rates of infection to decline with age (although non-teneral flies remain susceptible), (ii) a fraction of resistant flies, which may vary between sites, (iii) increased mortality of infected flies and (iv) variation in the maturation period. Models with these features can explain up to 97% of observed variance. Parameter estimates from published experimental data suggest that all may contribute in practice but that (i) and/or (ii) are likely to be the most important.

Antibiotics have been widely used to identify ribosomal activity in Trypanosoma brucei mitochondria. The validity of some of the results has been questioned because the permeability of the trypanosome cell membrane for some antibiotics was not adequately addressed. Here we describe translation inhibition experiments with digitonin-permeabilized trypanosomes to exclude diffusion barriers through the cell membrane. Using this system we were able to confirm, next to the eukaryotic and thus cycloheximide-sensitive translation system, the existence of a prokaryotic-type translational activity being cycloheximide resistant, chloramphenicol sensitive and streptomycin dependent. We interpret this observation analogous to what has been found for other eukarya as the independent protein synthesis activity of the mitochondrial organelle. We further examined the putative translational apparatus by using isokinetic density-gradient analysis of mitochondrial extracts. The 2 mitochondrially encoded rRNAs, the 9S and 12S rRNAs, were found to co-fractionate in a single RNP complex, approximately 80S in size. This complex disassembled at reduced MgCl2 concentrations into 2 unusually small complexes of 17·5S, containing the 9S rRNA, and 20S containing the 12S rRNA. A preliminary stoichiometry determination suggested a multicopy assembly of these putative subunits in a 2[ratio ]3 ratio (20S[ratio ]17·5S).

A benznidazole-resistant population of Trypanosoma cruzi, Y strain, was selected after 25 successive passages (8 months) in mice treated with a single high drug dose. Initially, the resistant parasites produced a low parasitaemia level and low mortality rate in infected mice. Thereafter, the parasitaemia level and mortality rate increased to the same value obtained for mice infected with the wild-type strain. Long-term treatment with benznidazole (100 mg/kg/day) cured 71–80% of mice infected with the wild-type strain. No cure was observed in mice infected with the selected resistant parasite population. Treatment with 500 mg/kg of benznidazole at peak parasitaemia cleared all blood parasites from mice infected with wild-type parasites. No effect on parasitaemia level was observed in mice infected with the selected parasites. Benznidazole-resistant parasites showed cross-resistance to different drugs. Contrary to wild type, all clones analysed from the resistant T. cruzi population were resistant to benznidazole. Without drug pressure the resistance phenotype of clones was far more stable than that presented by the resistant population. This work demonstrates, for the first time, the in vivo selection of a population and clones of T. cruzi resistant to benznidazole, and makes available an experimental model for the study of mechanisms of drug resistance in T. cruzi.

A cross-sectional study of bancroftian filariasis was conducted in 2 adjacent communities, Mvumoni and Kilore in Muhaka, Kwale District. Wuchereria bancrofti infection, clinical manifestations and anti-filarial IgG responsiveness were determined before the long rains, a time coinciding with a low transmission season. The prevalence of microfilaraemia increased gradually with age and was significantly higher in Kilore (24%) than in Mvumoni (6·3%, P<0·001). Similarly, the prevalence of antigenaemia increased with age and also was significantly higher in Kilore, 48·9% than in Mvumoni, 20·5% (P<0·001). Hydrocele, funiculitis, lymphangitis and lymphadenitis were also significantly more common in Kilore than in Mvumoni. In comparing the 2 communities, levels of IgG4 responsiveness in antigen-positive persons were higher in Kilore than Mvumoni (P=0·034), but this was related to higher antigen loads in persons in Kilore than in Mvumoni. In antigen-negative persons, anti-filarial antibodies of 3 IgG isotypes were significantly higher in Kilore than Mvumoni (P<0·001, for IgG1, IgG2, IgG4). These results emphasize the highly focal nature of bancroftian filariasis in this setting and demonstrate that anti-filarial antibody levels are related to transmission intensity.

The total lipid content of the dry weight of whole cysts and 2nd-stage juveniles (J2) of Globodera rostochiensis was 17·1% in dry cysts, 20·9% in cysts soaked in distilled water (DW), 20·3% in cysts that had been in potato root diffusate (PRD) for 7 days, 7·3% in cysts that had been in PRD for 28 days and 29·2% for hatched J2. The fatty acid composition of the total lipid did not differ between dry cysts, cysts in DW and cysts in PRD for 7 days. However, major differences in the fatty acid composition of all lipid classes were found between rehydrated cysts in PRD and freshly hatched J2. After hatching, the degree of saturation and the percentage of monounsaturated fatty acids decreased and the percentage of polyunsaturated fatty acids increased considerably, especially in the free fatty acid fraction, where C20[ratio ]1 showed an 8-fold decrease and C20[ratio ]4 a 33-fold increase. There was a difference in the fatty acid composition of cysts in PRD for 7 days and cysts in PRD for 28 days (after most of the J2 had hatched); with increased time in PRD the percentage of polyunsaturated fatty acids increased and the percentage of monounsaturated fatty acids decreased in all lipid classes. Differences in the fatty acid profiles between cysts in PRD for 28 days and hatched J2 were found mainly in the free fatty acid and the non-acidic phospholipid fractions. The free fatty acid fraction of the cysts was dominated by monounsaturated fatty acids (52%), whereas the same fraction of hatched J2 contained large amounts of polyunsaturated fatty acids (60%). These polyunsaturated fatty acids, especially C20[ratio ]4, might play an important part in nematode–plant interactions during infection.

Metacestodes of Hymenolepis diminuta affect several aspects of female reproductive physiology in Tenebrio molitor and such effects are mediated via the endocrine system. The effects on male reproduction are less well known and were studied with respect to the Bean-Shaped Accessory Glands (BAGs). The size and wet and dry weight of BAGs from infected and uninfected beetles were compared and rose to a plateau from 0–6 days post-emergence in uninfected beetles but in infected individuals continued to increase in both size and weight. These effects were density independent. Glands from both infected and uninfected beetles were assayed for trehalase activity measured by its ability to convert the sugar trehalose to glucose. The activity of this enzyme, per mg wet weight, was not affected by the parasite. However, total activity per gland increased in infected males. Total protein content and electrophoretic profiles of BAGs from infected and uninfected individuals showed no change in profile but showed an increase in all protein subunits per gland over a broad molecular weight range.

The effects of a parasitic infection with the nematode Nippostrongylus brasiliensis on the degradation rates of cytoplasmic tRNA, rRNA and mRNA in rats have been investigated by measuring the renal excretion rates of the modified RNA catabolites N6-threoninocarbonyladenosine, pseudouridine and 7-methylguanine. Between days 9 and 13 post-infection when the expulsion of N. brasiliensis is usually the most pronounced, the degradation rates of the different RNA classes were significantly higher than in the control rats (P<0·05) by, on average, +24% (tRNA), +34% (rRNA) and +26% (mRNA). We suspect that the elevated degradation rates of RNA are related to an increased production of reactive oxygen species by the host during the expulsion of N. brasiliensis.