Enzymes moonlight in a non-enzymatic capacity in a diverse variety of cellular processes. The discovery of these non-enzymatic functions is generally unexpected, and moonlighting enzymes are known in both prokaryotes and eukaryotes. Importantly, this unexpected multi-functionality indicates that caution might be needed on some occasions in interpreting phenotypes that result from the deletion or gene-silencing of some enzymes, including some of the best known enzymes from classic intermediary metabolism. Here, we provide an overview of enzyme moonlighting in parasitic protists. Unequivocal and putative examples of moonlighting are discussed, together with the possibility that the unusual biological characteristics of some parasites either limit opportunities for moonlighting to arise or perhaps contribute to the evolution of novel proteins with clear metabolic ancestry.

The intestinal parasite community of Arctic foxes (Vulpes lagopus) on the Svalbard archipelago in the High Arctic was investigated in relation to the abundance and distribution of intermediate hosts. Five species of cestodes (Echinococcus multilocularis, Taenia crassiceps, Taenia polyacantha, Taenia krabbei and Diphyllobothrium sp.), ascaridoid nematodes and one unidentified acanthocephalan species were found. The cestodes E. multilocularis, T. crassiceps and T. polyacantha all showed a decreasing prevalence in the fox population with increasing distance from their spatially restricted intermediate host population of sibling voles (Microtus levis). In addition, the prevalence of E. multilocularis in a sample from the vole population was directly related to the local vole abundance. The cestode T. krabbei uses reindeer as intermediate host, and its prevalence in female foxes was positively related to the density of reindeer (Rangifer tarandus platyrhyncus). Finally, the prevalence of the ascaridoid nematodes also decreased with increasing distance from the vole population, a finding that is consistent with the idea that voles are involved in transmission, most likely as paratenic hosts. The prevalence of the remaining species (Diphyllobothrium sp. and an unidentified acanthocephalan) was very low. We conclude that the distribution and abundance of intermediate host structure the gastrointestinal parasite community of the Arctic fox on the Svalbard archipelago.

Exponential decay in community similarity as a function of distance is a ubiquitous phenomenon in biogeography. Thus, for parasite communities, pairwise similarity decreases with increasing geographical distance between host populations. This biogeographical rule should also apply along other dimensions characterizing the separation between communities. Since host-switching and phylogenetic affinities among host species affect the evolution of parasite faunas across host phylogenetic space the same way as dispersal and environmental gradients affect the assembly of local communities in geographical space, an exponential decay in similarity of parasite faunas with increasing host phylogenetic distance should be observed. This prediction is tested using data on metazoan parasites of 45 species of Canadian freshwater fishes belonging to 5 families. Across all host species, pairwise similarity in the composition of parasite faunas decayed exponentially, though not strongly, with increasing phylogenetic distance between hosts (measured as the number of substitutions per site along DNA sequences). A meta-analysis of correlations computed for separate fish families indicates only a very weak overall relationship. Data distribution indicates that phylogenetically close host species tend to share many of their parasites, while phylogenetically distant hosts have roughly equal chances of harbouring very similar or very dissimilar parasite faunas. The same pattern was seen when monogenean and trematode parasites were analysed separately, whereas no significant decay was observed for cestodes or nematodes, suggesting different patterns of host-switching and parasite colonization among these taxa. The results show that similarity in species composition decreases, though weakly, with increasing distance in the same manner in phylogenetic space as it does in geographical space.

Among the topics of considerable interest concerning our understanding of the unusual biology of schistosomes is the sexual maturation of the female. The identification of genes coding for signal transduction proteins controlling essential steps of the pairing-dependent differentiation of the reproductive organs, vitellarium and ovary will help to substantiate our knowledge about this unique parasite. Furthermore, such signalling proteins could be potential targets to interfere with the development of this parasite to combat schistosomiasis since its pathology is caused by the eggs. This review summarises first post-genomic steps to elucidate the function of gonad-specific signalling molecules which were identified by homology-based cloning strategies, by in silico identification or by yeast two-hybrid interaction analyses, using a combination of novel techniques. These include the in vitro culture of adult schistosomes, their treatment with chemical inhibitors to block enzyme activity, the use of RNAi to silence gene function post-transcriptionally, and confocal laser scanning microscopy to study the morphological consequences of these experimental approaches. Finally, we propose a first model of protein networks that are active in the ovary regulating mitogenic activity and differentiation. Some of these molecules are also active in the testes of males, probably fulfilling similar roles as in the ovary.

The transforming growth factor-β (TGF-β) gene family regulates critical processes in animal development, and plays a crucial role in regulating the mammalian immune response. We aimed to identify TGF-β homologues from 2 laboratory model nematodes (Heligmosomoides polygyrus and Nippostrongylus brasiliensis) and 2 major parasites of ruminant livestock (Haemonchus contortus and Teladorsagia circumcincta). Parasite cDNA was used as a template for gene-specific PCR and RACE. Homologues of the TGH-2 subfamily were isolated, and found to differ in length (301, 152, 349 and 305 amino acids respectively), with variably truncated N-terminal pre-proteins. All contained conserved C-terminal active domains (>85% identical over 115 amino acids) containing 9 cysteine residues, as in C. elegans DAF-7, Brugia malayi TGH-2 and mammalian TGF-β. Surprisingly, only the H. contortus homologue retained a conventional signal sequence, absent from shorter proteins of other species. RT-PCR assays of transcription showed that in H. contortus and N. brasiliensis expression was maximal in the infective larval stage, and very low in adult worms. In contrast, in H. polygyrus and T. circumcincta, tgh-2 transcription is higher in adults than infective larvae. The molecular evolution of this gene family in parasitic nematodes has diversified the pre-protein and life-cycle expression patterns of TGF-β homologues while conserving the structure of the active domain.

Taeniid eggs contain an infective larval form of the parasite, known as the oncosphere, which has been found to be highly susceptible to attack by the host's immune system and this fact has been exploited in the development of highly effective vaccines. Relatively little is known about the structure of taeniid oncospheres and the localization of host-protective antigens within or on the oncosphere. Here, we briefly review the current state of knowledge of the structure of the oncosphere and present preliminary data on the localization of a host-protective antigen within the oncospheres of Taenia ovis. The precise localization of the antigens, in the context of a detailed knowledge of the ultrastructure of the parasite, may reveal the immune mechanisms by which the taeniid parasites are killed by vaccine-induced immune responses, which, in turn, may provide clues about how vaccines could be developed against other parasitic helminths.

The presence or absence of parasites within host populations is the result of a complex of factors, both biotic and abiotic. This study uses a non-parametric classification tree approach to evaluate the relative importance of key abiotic and biotic drivers controlling the presence/absence of parasites with complex life cycles in a sentinel, the common killifish Fundulus heteroclitus. Parasite communities were classified from 480 individuals representing 15 fish from 4 distinct marsh sites in each of 4 consecutive seasons between 2006 and 2007. Abiotic parameters were recorded at continuous water monitoring stations located at each of the 4 sites. Classification trees identified the presence of benthic invertebrate species (Gammarus sp. and Littorina sp.) as the most important variables in determining parasite presence: secondary splitters were dominated by abiotic variables including conductance, pH and temperature. Seventy percent of hosts were successfully classified into the correct category (infected/uninfected) based on only these criteria. The presence of competent definitive hosts was not considered to be an important explanatory variable. These data suggest that the most important determinant of the presence of these parasite populations in the common killifish is the availability of diverse communities of benthic invertebrates.

Totipotent somatic stem cells (neoblasts) are key players in the biology of flatworms and account for their amazing regenerative capability and developmental plasticity. During recent years, considerable progress has been made in elucidating molecular features of neoblasts from free-living flatworms, whereas their role in parasitic species has so far merely been addressed by descriptive studies. Very recently, however, significant advances have been made in the in vitro culture of neoblasts from the cestode Echinococcus multilocularis. The isolated cells proved capable of generating mature metacestode vesicles under laboratory conditions in a manner that closely resembles the oncosphere-metacestode transition during natural infections. Using the established neoblast cultivation protocols, combined with targeted manipulation of Echinococcus genes by RNA-interference, several fundamental questions of host-dependent parasite development can now be addressed. Here, I give an overview of current cultivation techniques for E. multilocularis neoblasts and present experimental approaches to study their function. Furthermore, I introduce the E. multilocularis genome sequencing project that is presently in an advanced stage. The combined input of data from the E. multilocularis sequencing project, stem cell cultivation, and recently initiated attempts to genetically manipulate Echinococcus will provide an ideal platform for hypothesis-driven research into cestode development in the next years.

The generative mechanism(s) of aggregation and predisposition to Ascaris lumbricoides and A. suum infections in their host population are currently unknown and difficult to elucidate in humans and pigs for ethical/logistical reasons. A recently developed, optimized murine model based on 2 inbred strains, putatively susceptible (C57BL/6j) and resistant (CBA/Ca) to infection, was exploited to elucidate further the basis of the contrasting parasite burdens, most evident at the pulmonary stage. We explored the kinetics of early infection, focusing on the composite lobes of the liver and lung, over the first 8 days in an effort to achieve a more detailed understanding of the larval dispersal over time and the point at which worm burdens diverge. Larval recoveries showed a heterogenous distribution among the lobes of the lungs, being higher in the right lung of both strains, and in the susceptible strain larvae accumulating preferentially in 2 (caudal and middle) of the 4 lobes. Total larval burdens in these 2 lobes were largely responsible for the higher worm burdens in the susceptible strain. While total lung larval recoveries significantly differed between mouse strains, a difference in liver larval burdens was not observed. However, an earlier intense inflammatory response coupled with more rapid tissue repair in the hepatic lobes was observed in CBA/Ca mice, in contrast to C57BL/6j mice, and it is possible that these processes are responsible for restricting onward pulmonary larval migration in the resistant genotype.