Mitochondria of the malaria parasite Plasmodium falciparum are morphologically different between the asexual and sexual blood stages (gametocytes). In this paper recent findings of mitochondrial heterogeneity are reviewed based on their ultrastructural characteristics, metabolic activities and the differential expression of their genes in these 2 blood stages of the parasite. The existence of NADH dehydrogenase (complex I), succinate dehydrogenase (complex II), cytochrome c reductase (complex III) and cytochrome c oxidase (complex IV) suggests that the biochemically active electron transport system operates in this parasite. There is also an alternative electron transport branch pathway, including an anaerobic function of complex II. One of the functional roles of the mitochondrion in the parasite is the coordination of pyrimidine biosynthesis, the electron transport system and oxygen utilization via dihydroorotate dehydrogenase and coenzyme Q. Complete sets of genes encoding enzymes of the tricarboxylic acid cycle and the ATP synthase complex are predicted from P. falciparum genomics information. Other metabolic roles of this organelle include membrane potential maintenance, haem and coenzyme Q biosynthesis, and oxidative phosphorylation. Furthermore, the mitochondrion may be a chemotherapeutic target for antimalarial drug development. The antimalarial drug atovaquone targets the mitochondrion.

Malaria is a major health concern particularly in Africa which has about 90% of the worldwide annual clinical cases. The increasing number of drug-resistant Plasmodium falciparum justifies the search for new drugs in this field. Antimalarial activity of 2-substituted 6-nitro- and 6-amino-benzothiazoles and their anthranilic acids has been tested. An in vitro study has been performed on W2 and 3D7 strains of P. falciparum and on clinical isolates from malaria-infected patients. Toxicity has been assessed on THP1 human monocytic cells. For the most active drug candidates, the in vitro study was followed by in vivo assays on P. berghei-infected mice and by in vitro assays in order to determine the stage-dependency and the mechanism of action. Of 39 derivatives tested in vitro, 2 had specific antimalarial properties. Each compound was active on all stages of the parasite, but one was markedly active on mature schizonts, while the other was more active on young schizont forms. Both drugs were also active on mitochondrial membrane potential. In vivo data confirmed efficiency with a sustained decrease of parasitaemia. Products A12 and C7 may be considered as potential antimalarial worthy of further chemical and biological research.

The biodiversity of insect trypanosomes is largely unknown, resulting in significant gaps in the understanding of pathogen evolution. A culture-independent preliminary survey of trypanosomatid fauna was conducted for the parasites of Heteroptera (Hemiptera) from several localities in Costa Rica. Trypanosomatid infections were detected by light microscopy of smeared gut contents. Out of 257 insects representing 6 families, infections were found in 62 cases; cultures were obtained for 29 new isolates. Gut material from infected hosts was preserved in the field using an SDS–EDTA buffer solution for subsequent DNA extraction in the laboratory. PCR amplification of the trypanosomatid-specific spliced leader (SL) RNA gene repeats was successful for 60 field samples. Eighteen distinct SL RNA typing units were identified in a set of 28 samples analysed in detail. Cluster analysis indicated that these typing units were unique and thus could represent new species and, in some cases, new genera. This study reveals only a minor fraction of the trypanosomatid biodiversity, which is anticipated to be high.

Phylogenetic relationships among Trypanosoma rangeli isolates from man, wild mammals and triatomine bugs from widespread geographical origin were inferred by comparison of the small subunit of ribosomal gene sequences. The phylogenetic trees indicated that the subgenus Herpetosoma is polyphyletic and strongly supported division of this group into two monophyletic lineages, one made up of T. rangeli, T. rangeli-like and allied species and other consisting of T. lewisi and related taxa. Based on phylogenetic analysis, morphology, behaviour in vertebrate and invertebrate hosts and epidemiology we propose: a) the validation of Herpetosoma as a taxon comprised only for species of group lewisi and the maintenance of T. lewisi as the type-species of this subgenus; b) the classification of T. rangeli, T. rangeli-like and allied species into a ‘T. rangeli-clade’ more closely related to Schizotrypanum than to T. lewisi or T. brucei. The phylogenetic tree disclosed at least 4 groups within the clade T. rangeli, all confirmed by polymorphism of the internal transcribed spacer, thus conferring for the first time phylogenetic support to groups of T. rangeli and corroborating the high complexity of this taxon. Grouping was independent of their mammalian host-species and geographical origin, indicating that other factors are determining this segregation.

In previous studies, we demonstrated that CRA and FRA recombinant proteins, used for diagnosis of Chagas' disease, elicited a humoral immune response in susceptible and resistant mice. To understand better the immune response to these proteins, we have evaluated, the cellular immune response in CRA- and in FRA-immunized BALB/c and C57BL/6 mice. A specific cellular lymphoproliferative response was observed in both strains of mice. Spleen cell cultures mainly from CRA-immunized C57BL/6 and FRA-immunized BALB/c mice produced high levels of IFN-γ, indicating the induction of a Type 1 immune response. Regarding the T cell subsets, CD4+ T cells were the major source of IFN-γ in CRA- and FRA-immunized mice. These results suggest that CRA and FRA are important immunogens in inducing a Type 1 immune response and that they may be considered as potential vaccine antigens.

We investigated the genotypic composition of the digenetic parasite Schistosoma mansoni for its adult stages within the definitive host (the wild rat, Rattus rattus) and for the larval stages within the intermediate host (the snail, Biomphalaria glabrata) both collected at the same transmission site. Our analyses are based upon the recognition and distribution of 200 different multilocus genotypes generated by RAPD markers. While intramolluscan larval infrapopulations are characterized by a low infection rate (0·6% on average) and low intra-host genetic diversity (1·1 genotype on average per infected snail), adult infrapopulations within rats showed a high infection rate (94%) and a substantial intra-host genetic diversity (34 genotypes on average) linked to high intensities (160 worms per host on average). A single definitive host bearing 105 different genotypes harboured 52% of the total genetic diversity detected within the whole parasite population. Analysis of the genetic data allowed the identification of various ecological, behavioural and immunological factors which are likely to enhance transmission of multiple parasite genotypes towards the vertebrate hosts. From the distribution of repeated identical multilocus genotypes within the parasite population and among the hosts, we have inferred different parameters of the cercarial transmission efficiency as well as patterns and processes by which vertebrate hosts acquire infection in the field.

Stage-specific alternative splicing of the heat-shock transcription factor of Schistosoma mansoni (SmHSF) generates isoforms with structural diversity that may modulate the activity of SmHSF at different life-stages, and thus may regulate the expression of different genes at different developmental stages. RT-PCR, cloning and DNA-sequence analyses showed stage-specific alternative splicing inside the DNA-binding domain (DBD) involving introns I1 and I2, and beyond the DBD involving introns I4a and I7. Retention of introns I2 and I4a would inactivate SmHSF since they contain termination codons. Retention of intron I1 would add 11 amino acids inside the DBD and may change the DNA-binding specificity of SmHSF; intron I7 would add 13 amino acids to the effector region of HSF. Retention of introns was more pronounced in cercariae (larval stage living in water) than in adult worms (parasitic form in mammals). The isoforms were expressed in bacteria, but functional evaluation was not feasible, because only the isoform lacking introns was soluble while isoforms with introns were insoluble. However, stage-specific alternative splicing that changed HSF function in vivo was evidenced in intact cercariae. The cercarial SmHSF mRNA was enriched with introns I2 and I4a that contain termination codons. Therefore, translation of the SmHSF mRNA was impaired, and the SmHSF protein was undetectable. Consequently, the HSP70 gene could not be transcribed, and the HSP70 mRNA was missing. Alternative splicing was observed for short DNA segments (33–45 bp) bound by splice signals, located in the coding region. These are not bona fida exons since they are not flanked by introns. Yet, they are not regular introns since they are often found in mature mRNA. Alternative splicing of these DNA segments caused structural diversity that could modulate the function of the gene product.

Pre-natal infection of Schistosoma japonicum in pigs may prove to be a useful model in shedding light on human pre-natal schistosomiasis. This study describes the effects of immune colostrum on worm burdens, tissue egg counts, liver pathology and crude worm or egg antigen-specific IgG and IgA responses, in groups of pigs pre-natally, pre-natally+post-natally or post-natally exposed to S. japonicum. Results suggest that pre-natal exposure and immune colostrum did not affect the establishment of a post-natal challenge infection. However, immune colostrum seemed to increase the levels of septal fibrosis in pre-natally exposed pigs. These findings indicate that further investigations will prove valuable, elucidating the influence of the parasitological and immunological status of the sow, on pre-natally exposed pigs, and on the ability of these pigs to develop resistance against S. japonicum later in life.

The role of acquired immunity in lymphatic filariasis is uncertain. Assuming that immunity against new infections develops gradually with accumulated experience of infection, models predict a decline in prevalence after teenage or early adulthood. A strong indication for acquired immunity was found in longitudinal data from Pondicherry, India, where Mf prevalence was highest around the age of 20 and declined thereafter. We reviewed published studies from India and Subsaharan Africa to investigate whether their age-prevalence patterns support the models with acquired immunity. By comparing prevalence levels in 2 adult age groups we tested whether prevalence declined at older age. For India, comparison of age groups 20–39 and 40+ revealed a significant decline in only 6 out of 53 sites, whereas a significant increase occurred more often (10 sites). Comparison of older age groups provided no indication that a decline would start at a later age. Results from Africa were even more striking, with many more significant increases than declines, irrespective of the age groups compared. The occurrence of a decline was not related to the overall Mf prevalence and seems to be a chance finding. We conclude that there is no evidence of a general age-prevalence pattern that would correspond to the acquired immunity models. The Pondicherry study is an exceptional situation that may have guided us in the wrong direction.

This paper describes the structure of the microfilarial reservoir of Loa loa in an endemic population of central Cameroon. The possible effects of age and sex on the prevalence and intensity of microfilaraemia have been explored. Logistic analysis showed that the prevalence of microfilaraemia increased significantly with age, reaching 60% in the oldest males. This result suggests that the figure commonly reported, according to which only one third of the infected individuals were microfilaraemic, should be reconsidered; in addition, as part of surveys of loiasis, crude microfilaraemia prevalence values should be replaced by adjusted ones. The intensity of infection did not show any age-specific change. As a result, even if the oldest members of the male population are clearly the most at risk of developing post-ivermectin serious adverse reactions, especially Loa-encephalopathy, the other members of the population are not risk-free. Therefore, in those areas where the African Programme for Onchocerciasis Control is undertaking regular mass distributions of ivermectin for onchocerciasis control, and where loiasis is co-endemic, no subpopulation should be excluded from surveillance and monitoring during community directed treatments with ivermectin.

Thelazia callipaeda (Spirurida, Thelaziidae) eyeworm causes ocular infection in carnivores and humans in the Far East; this infection has been recently reported also in Europe – northern and southern Italy – in dogs, cats and foxes. The natural vector/s of T. callipaeda is/are unknown and the development of the nematode in its definitive hosts is limited to an experimental trial on dogs. To contribute new insights into the development of T. callipaeda in the definitive host in field conditions, eyeworms were collected from naturally infected dogs from an area with a high prevalence of infection (up to 60·14%) in the Basilicata region of southern Italy, from January 2002 to December 2003. Conjunctival secretions were also collected and examined for the presence of immature stages. The presence of blastomerized eggs throughout the period – except for the months from May to November – indicates a seasonality in the reproductive activity of T. callipaeda, coinciding with the presence/absence of the vector. In fact, 1st-stage larvae were found in the lachrymal secretions of dogs in summer (June–July 2002 and 2003), ready to be ingested by flies feeding about the eyes. The evidence of 4th-stage larvae in March 2002 and April, July and October 2003 may be accounted for by the presence of flies that act as intermediate hosts of T. callipaeda from early spring to early autumn. The presence of immature stages in October indicates an overlapping generation of nematodes and a 2nd cycle of vector infection. This basic knowledge of the development of T. callipaeda will hopefully help future epidemiological studies to identify the intermediate hosts and define the likely risk for vectors in field conditions.

In theory there should be a strong coupling between host and parasite population sizes. Here, we investigated population size and structure in 3 species of acanthocephalans, Corynosoma semerme, C. strumosum and C. magdaleni, in ringed seals (Phoca hispida) from the Bothnian Bay over a period of more than 20 years. During this period, seal numbers first decreased markedly and then increased steadily; at the same time, a paratenic fish host particularly important for C. strumosum has gradually disappeared from the bay due to decreasing salinity. We found no evidence that the mean abundance of any of the 3 acanthocephalan species changed significantly over time, nor was there any relationship between parasite abundance at any point in time and seal numbers in the corresponding year. Based on the proportion of sexually mature female worms per infrapopulation, and on relationships between the sex ratio of worms and infrapopulation size, both C. magdaleni and C. semerme appear to be doing well, independently of the population size of their seal definitive hosts. In contrast, perhaps because of the loss of its main paratenic host, C. strumosum appears more at risk in the Bothnian Bay. Our results show that in complex natural systems, there are not necessarily simple, direct links between definitive host population size or density, and parasite population dynamics.

Chemical cues are so important in the recognition mechanism of social insects that most social parasites (which rely on hosts to rear their brood) have been documented as overcoming the mechanism by which colony residents recognize non-nestmates, by mimicking the odour of the usurped colony. We simulated in the laboratory the process by which the obligate social parasite, Polistes semenowi, invades nests of the host species, Polistes dominulus, in the field and analysed the epicuticular lipid layer before and after host nest usurpation. The experiment documents that P. semenowi social parasites have an epicuticular hydrocarbon pattern which is very similar to that of their host but, after entering host colonies, parasites mimic the odour of the colonies they invade, to the point that they perfectly match the hydrocarbon profile peculiar to the colony they entered. However, both before and after host nest invasion, parasites show a tendency to possess diluted recognition cues with respect to their hosts.