This study investigated the significance of serum complement on transmission-reducing activity (TRA) of field sera from 24 infected Plasmodium falciparum gametocyte carriers (from Cameroon) against cultured NF54 P. falciparum. Laboratory-reared Anopheles stephensi were given infectious blood meals prepared either with sera from naïve Dutch donor (AB type) or pair-matched field serum samples, both with and without active complement. TRA of serum factors and host complement on mosquito infection rate and oocyst intensity were divided into the various components involved in the early stages of sporogony. The majority (>80%) of sera tested showed positive antibody titres to Pfs230, the relevant complement-dependent target of transmission-reducing mechanisms. Regardless of the presence of active complement, bloodmeals with field sera exhibited significantly lower infection rates and oocyst intensity than the control group. Serological reactivity in Capture-ELISA against Pfs230 was significantly correlated with the reduction of parasite infectivity. Contrary to our expectation, the presence of active complement in the mosquito bloodmeal did not increase parasite losses and therefore the magnitude of transmission reduction by individual immune sera. Our findings on P. falciparum are consistent with previous studies on animal hosts of Plasmodium, indicating that early P. falciparum sporogonic stages may be insensitive to the antibody-dependent pathways of complement in human serum.

The heteroxenous protozoan parasite Toxoplasma gondii is transmitted from the intermediate host (any warm-blooded animal) to the definitive host (members of the felidae) by carnivory. The infected intermediate hosts develop several specific behavioural changes that are usually considered products of manipulative activity of the parasite aimed to increase the probability of its transmission to the definitive host. Among other changes, the infected rodents were shown to have impaired learning capability. All previous studies were done 2–6 weeks after the infection. Therefore, it was difficult to resolve whether the observed impairment of learning processes was a result of acute or latent toxoplasmosis, i.e. whether it was a side-effect of the disease or a product of manipulation activity. Here we studied the learning capability of Toxoplasma-infected mice in the static rod test and 8-arm radial maze test and their spontaneous activity in the wheel running test 10 weeks after the infection. The infected mice achieved worse scores in the learning tests but showed higher spontaneous activity in the wheel running test. However, a detailed study of the obtained results as well as of the data reported by other authors suggested that the differences between infected and control mice were a result of impaired ability to recognize novel stimuli rather than of impaired learning capacity in animals with latent toxoplasmosis.

The dense granule antigen 4 (GRA4) is known as an immundominant antigen of Toxoplasma gondii and, therefore, is considered as a vaccine candidate. For further evaluation of its vaccine effect, a recombinant plasmid and vaccinia virus, both expressing GRA4, were constructed, and a heterologous prime-boost vaccination regime was performed in a mouse model. The mice immunized with the heterologous prime-boost vaccination regime showed a high level of specific antibody response against GRA4 and a significantly high level of gamma interferon (IFN-γ) production and survived completely against a subsequent challenge infection with a lethal dose of T. gondii. In addition, the formation of cysts was inhibited in the mice vaccinated with the heterologous prime-boost vaccination regime. These results demonstrate that the heterologous prime-boost vaccination regime using DNA and a vaccinia virus, both expressing GRA4, could induce both humoral and cellular immune responses and provide effective protection against lethal acute and chronic T. gondii infections in mice.

Cyclin-dependent kinases (CDKs) are essential for the regulation of the eukaryotic cell cycle. A number of chemicals, which selectively inhibit the CDK activities, have been synthesized for the development of anti-cancer drugs. This report describes the inhibitory effect of purine derivatives known to be CDK inhibitors on the asexual growth of Babesia bovis. The 4 compounds, roscovitine, purvalanol A, CGP74514A, and CDK2 Inhibitor II, showed significantly suppressive effects on the in vitro growth of B. bovis. Three (roscovitine, purvalanol A, and CDK2 Inhibitor II) showed an inhibitory effect on the early stages of intraerythrocytic development of B. bovis. CGP74514A (CDK1-specific inhibitor) blocked the erythrocyte invasion by merozoites. Our data suggest the chemotherapeutic potential of the CDK inhibitors for babesiosis, and the target molecules of the compounds would participate in the process of successful erythrocyte invasion or intraerythrocytic development of B. bovis.

Parasitic infection is often associated with changes in host life-history traits, such as host development. Many of these life-history changes are ultimately thought to be the result of a depletion or reallocation of the host's resources driven either by the host (to minimize the effects of infection) or by the parasite (to maximize its growth rate). In this paper we investigate the energetic budget of Aedes aegypti mosquito larvae infected by Vavraia culicis, a microsporidian parasite that transmits horizontally between larvae, and which has been previously shown to reduce the probability of pupation of its host. Our results show that infected larvae have significantly less lipids, sugars and glycogen than uninfected larvae. These differences in resources were not due to differences in larval energy intake (feeding rate) or expenditure (metabolic rate). We conclude that the lower energetic resources of infected mosquitoes are the result of the high metabolic demands that microsporidian parasites impose on their hosts. Given the fitness advantages for the parasite of maintaining the host in a larval stage, we discuss whether resource depletion may also be a parasite mechanism to prevent the pupation of the larvae and thus maximize its own transmission.

Vertically transmitted parasites may have positive, neutral or negative effects on host fitness, and are also predicted to exhibit sex-specific virulence to increase the proportion or fitness of the transmitting sex. We investigated these predictions in a study on the survival and sex ratio of offspring of the amphipod Gammarus roeseli from females infected by the vertically transmitted microsporidia Nosema granulosis. We found, to our knowledge, the first evidence for a positive relationship between N. granulosis infection and host survival. Infection was associated with sex ratio distortion, not by male-killing, but probably by parasite-induced feminization of putative G. roeseli males. This microsporidia also feminizes another amphipod host, Gammarus duebeni, which is phylogenetically and biogeographically distant from G. roeseli. Our study suggests that the reproductive system of gammarids is easily exploited by these vertically-transmitted parasites, although the effects of infections on host fitness may depend on specific host-parasite species interactions.

The ability of the larval forms of Schistosoma mansoni to invade and parasitize their molluscan host, Biomphalaria glabrata, is determined by a multitude of factors. In this study we sought to elucidate the possible mechanisms by which the invading larvae are able to counteract the potentially harmful oxidative environment presented by the host upon initial miracidial infection. This was attempted by examining the gene expression profile of parasite antioxidant enzymes of the linked glutathione-(GSH) thioredoxin (Trx) redox pathway during early intramolluscan larval development. Three such enzymes, the peroxiredoxins (Prx1, Prx2 and Prx3) were examined as to their activity and sites of expression within S. mansoni miracidia and in vitro-cultured mother sporocysts. Results of these studies demonstrated that the H2O2-reducing enzymes Prx1 and 2 are upregulated during early mother sporocyst development compared to miracidia. Immunolocalization studies further indicated that Prx1 and Prx2 proteins are expressed within the apical papillae of miracidia and tegumental syncytium of sporocysts, and are released with parasite excretory-secretory proteins (ESP) during in vitro larval transformation. Removal of Prx1 and Prx2 from larval ESP by immunoabsorption significantly reduced the ability of ESP to breakdown exogenous H2O2, thereby directly linking ESP Prx proteins with H2O2-scavenging activity. Moreover, exposure of live sporocysts to exogenous H2O2 stimulated an upregulation of Prx1 and 2 gene expression suggesting the involvement of H2O2–responsive elements in regulating larval Prx gene expression. These data provide evidence that Prx1 and Prx2 may function in the protection of S. mansoni sporocysts during the early stages of infection.

We studied the effect of density on feeding success of 2 fleas, Xenopsylla conformis and Xenopsylla ramesis, when exploiting rodents Meriones crassus and Gerbillus dasyurus. We tested 2 alternative hypotheses: (i) that intraspecific interference competition occurs and, thus, feeding success of a flea decreases with an increase in density and (ii) that facilitation via suppression of a host defence system occurs and thus, feeding success of a flea increases with an increase in density. The mean size of a bloodmeal and the proportion of highly engorged individuals in X. conformis feeding on both hosts were affected by density. When on G. dasyurus, both the size of a bloodmeal and the proportion of highly engorged individuals were lower at low (5–15 fleas per host) than at high (25–50 fleas per host) densities. The opposite was true when this flea fed on M. crassus. The mean bloodmeal size and proportions of highly engorged X. ramesis parasitizing either host were not affected by flea density. This study showed that the density dependence of feeding success of a flea (a) varied both between fleas and within-fleas between hosts and (b) indicated either intraspecific competition or facilitation via the host in a particular flea-host association.

We report 21 thelastomatoid species parasitizing 31 described and 5 undescribed geoscapheine and panesthiine cockroaches, representing all but 1 of the known species of these subfamilies in Australia. The nematodes have 3 distinct patterns of host distribution: dominant, moderate and rare. The 4 dominant species, Cordonicola gibsoni, Leidynemella fusiformis, Travassosinema jaidenae and Aoruroides queenslandensis, are highly prevalent, found in nearly all host species examined, and broadly distributed. The 8 moderate species have lower prevalences but are still widely distributed. Many of these species are more common in one host subfamily than the other. The remaining 9 rare species have highly restricted host and geographical distributions. Six of the 21 species are exclusive to geoscapheines, 5 to panesthiines and 10 are shared. These patterns suggest that most of the reported thelastomatoid species are generalists rather than specialists, that host-specificity within this group is low and that co-evolutionary speciation has had little, if any, impact on structuring the thelastomatoid fauna of Australian burrowing cockroaches. In a broader context, this study provides the first comprehensive examination of the role of coevolutionary speciation and host specificity in regulating the distribution of pinworms in arthropods.

In this study, we examined the effects of local climate aridity on the richness and composition of the thelastomatoid (Nematoda: Oxyurida) guild parasitizing the Australian giant burrowing cockroach, Macropanesthia rhinoceros (Blattodea: Geoscapheinae). In total, 9 thelastomatoid species parasitized this cockroach in north-eastern Australia (Queensland). Local observed richness ranged from 3 species (in Cooktown, Magnetic Island, Maiden Springs and Whitsunday Island) to 7 species (in Rochford Scrub). The lowest richness occurred in both relatively wet and dry climates, and the highest richness was in moderate climates. Three species, Cordonicola gibsoni, Leidynemella fusiformis and Travassosinema jaidenae, were found at all 13 collection sites. One species, Geoscaphenema megaovum, was found exclusively in dry to moderate climates. The remaining species, Blattophila sphaerolaima, Coronostoma australiae, Desmicola ornata, Hammerschmidtiella hochi and Jaidenema rhinoceratum, were found in moderate climates only. We hypothesize that the egg is the stage in the thelastomatoid life-cycle most vulnerable to the effects of adverse climate and that the geographical distribution for each species is, in part, bound by environments that are too dry, resulting in egg desiccation, and by environments that are too wet, resulting in decreased oxygen uptake across the egg-shell and in osmotic lysing.

Gastrointestinal (GI) nematodes are important disease-causing organisms, controlled primarily through treatment with synthetic drugs, but the efficacy of these drugs has declined due to widespread resistance, and hence new drugs, with different modes of action, are required. Some medicinal plants, used traditionally for the treatment of worm infections, contain cysteine proteinases known to damage worms irreversibly in vitro. Here we (i) confirm that papaya latex has marked efficacy in vivo against the rodent gastrointestinal nematode, Heligmosomoides polygyrus, (ii) demonstrate the dose-dependent nature of the activity (>90% reduction in egg output and 80% reduction in worm burden at the highest active enzyme concentration of 133 nmol), (iii) establish unequivocally that it is the cysteine proteinases that are the active principles in vivo (complete inhibition of enzyme activity when pre-incubated with the cysteine proteinase-specific inhibitor, E-64) and (iv) show that activity is confined to worms that are in the intestinal lumen. The mechanism of action was distinct from all current synthetic anthelmintics, and was the same as that in vitro, with the enzymes attacking and digesting the protective cuticle. Treatment had no detectable side-effects on immune cell numbers in the mucosa (there was no difference in the numbers of mast cells and goblet cells between the treated groups) and mucosal architecture (length of intestinal villi). Only the infected and untreated mice had much shorter villi than the other 3 groups, which was a consequence of infection and not treatment. Plant-derived cysteine proteinases are therefore prime candidates for development as novel drugs for the treatment of GI nematode infections.

Molecular phylogenetic analyses of 113 taxa representing Ascaridida, Rhigonematida, Spirurida and Oxyurida were used to infer a more comprehensive phylogenetic hypothesis for representatives of ‘clade III’. The posterior probability of multiple alignment sites was used to exclude or weight characters, yielding datasets that were analysed using maximum parsimony, likelihood, and Bayesian inference methods. Phylogenetic results were robust to differences among inference methods for most high-level taxonomic groups, but some clades were sensitive to treatments of characters reflecting differences in alignment ambiguity. Taxa representing Camallanoidea, Oxyurida, Physalopteroidea, Raphidascarididae, and Skrjabillanidae were monophyletic in all 9 analyses whereas Ascaridida, Ascarididae, Anisakidae, Cosmocercoidea, Habronematoidea, Heterocheilidae, Philometridae, Rhigonematida and Thelazioidea were never monophyletic. Some clades recovered in all trees such as Dracunculoidea and Spirurina included the vast majority of their sampled species, but were non-monophyletic due to the consistent behaviour of one or few ‘rogue’ taxa. Similarly, 102 of 103 clade III taxa were strongly supported as monophyletic, yet clade III was paraphyletic due to the grouping of Truttaedacnitis truttae with the outgroups. Mapping of host ‘habitat’ revealed that tissue-dwelling localization of nematode adults has evolved independently at least 3 times, and relationships among Spirurina and Camallanina often reflected tissue predilection rather than taxonomy.

Newborn larvae (NBL) and adult (Ad) stage-specifically expressed genes or members of gene families of Trichinella spiralis were identified by suppression subtractive hybridization (SSH)†. Six cDNA clones were identified as NBL stage-specific, including 1 member of the T. spiralis gene family encoding glutamic acid-rich proteins, 2 clones encoding novel serine proteases, 2 closely related clones encoding proteins that are members of a deoxyribonuclease II (DNase II)-like family and 1 clone with no similarity to known genes. Four stage-specific clones encoding homologues of retinoid X receptor, caveolin, C2H2 type zinc finger protein and a putative protein with no homology to known sequences were obtained from 3-day-old adult worms. One gene specifically up-regulated in the 5-day-old adult worms encoding a putative cuticle collagen was also identified.

Cyclic GMP (cGMP) is responsible for various cellular functions including signal pathways and it acts as a mediator for nitric oxide (NO). In order to evaluate the anthelmintic efficacy of the plant-derived isoflavones, the crude peel extract of Flemingia vestita and pure genistein were tested with respect to the activity of nitric oxide synthase (NOS), NO efflux and the cGMP concentration in Rallietina echinobothrida, the cestode parasite of domestic fowl. For comparison, the parasites were also treated with genistein (the major isoflavone present in the crude peel extract), sodium nitroprusside (SNP), a known NO donor, and praziquantel (PZQ), the reference drug. At the time of onset of paralysis in the parasite, the activity of NOS showed a significant increase (35–46%) and a 2-fold increase of NO efflux into the incubation medium in the treated worms in comparison to the respective controls. The cGMP concentration in the parasite tissue increased by 46–84% in the treated test worms in comparison to the controls. The results show that the isoflavones, genistein in particular, from the crude peel extract of F. vestita influence the cGMP concentration in the parasite tissue, which plays a major role in the downstream signal pathways.

Genetic variation was examined in the anoplocephalid cestode Progamotaenia festiva, from Australian marsupials, in order to test the hypothesis that P. festiva, is a complex of sibling species and to assess the extent of host switching reported previously based on multilocus enzyme electrophoresis (MEE). Polymerase chain reaction (PCR)-based single-strand conformational polymorphism (SSCP) was used for the analysis of sequence variation in the cytochrome c oxidase subunit 1 (cox1) gene among 179 specimens of P. festiva (identified based on morphology and predilection site in the host) from 13 different host species, followed by selective DNA sequencing. Fifty-three distinct sequence types (haplotypes) representing all specimens were defined. Phylogenetic analyses of these sequence data (utilizing maximum parsimony and neighbour-joining methods) revealed 12 distinct clades. Other heterologous species, P. ewersi and P. macropodis, were used as outgroups and the remaining bile-duct inhabiting species, P. diaphana and P. effigia, were included in the analysis for comparative purposes. The latter 2 species were nested within the clades representing P. festiva. Most clades of P. festiva identified were restricted to a single host species; one clade primarily in Macropus robustus was also found in the related host species M. antilopinus in an area of host sympatry; another clade occurring primarily in M. robustus occurred also in additional kangaroo species, M. rufus and M. dorsalis. High levels of genetic divergence, the existence of distinct clades and their occurrence in sympatry provide support for the hypothesis that P. festiva represents a complex of numerous species, most of which, but not all, are host specific. Three distinct clades of cestodes were found within a single host, M. robustus, but there was no evidence of within-host speciation.