International journal for parasitology最新文献

The interaction between pathogens and vectors’ physiology can impact parasite transmission. Studying this interaction at the molecular level can help in developing control strategies. We study leishmaniases, diseases caused by Leishmania parasites transmitted by sand fly vectors, posing a significant global public health concern. Lipophosphoglycan (LPG), the major surface glycoconjugate of Leishmania, has been described to have several roles throughout the parasite’s life cycle, both in the insect and vertebrate hosts. In addition, the sand fly midgut possesses a rich microbiota expressing lipopolysaccharides (LPS). However, the effect of LPG and LPS on the gene expression of sand fly midgut proteins or immunity effectors has not yet been documented. We experimentally fed Lutzomyia longipalpis and Phlebotomus papatasi sand flies with blood containing purified LPG from Leishmania infantum, Leishmania major, or LPS from Escherichia coli. The effect on the expression of genes encoding gut proteins galectin and mucin, digestive enzymes trypsin and chymotrypsin, and antimicrobial peptides (AMPs) attacin and defensins was assessed by quantitative PCR (qPCR). The gene expression of a mucin-like protein in L. longipalpis was increased by L. infantum LPG and E. coli LPS. The gene expression of a galectin was increased in L. longipalpis by L. major LPG, and in P. papatasi by E. coli LPS. Nevertheless, the gene expression of trypsins and chymotrypsins did not significantly change. On the other hand, both L. infantum and L. major LPG significantly enhanced expression of the AMP attacin in both sand fly species and defensin in L. longipalpis. In addition, E. coli LPS increased the expression of attacin and defensin in L. longipalpis. Our study showed that Leishmania LPG and E. coli LPS differentially modulate the expression of sand fly genes involved in gut maintenance and defence. This suggests that the glycoconjugates from microbiota or Leishmania may increase the vector’s immune response and the gene expression of a gut coating protein in a permissive vector.

Malaria remains the most important arthropod-borne infectious disease globally. The causative agent, Plasmodium, is a unicellular eukaryote that develops inside red blood cells. Identifying new Plasmodium parasite species that infect mammalian hosts can shed light on the complex evolution and diversity of malaria parasites. Bats feature a high diversity of microorganisms including seven separate genera of malarial parasites. Three species of Plasmodium have been reported so far, for which scarce reports exist. Here we present data from an investigation of Plasmodium infections in bats in the western Guinean lowland forest in Sierra Leone. We discovered a new Plasmodium parasite in the horseshoe bat Rhinolophus landeri. Plasmodium cyclopsi infections in a member of leaf-nosed bats, Doryrhina cyclops, exhibited a high prevalence of 100%. Phylogenetic analysis of complete mitochondrial genomes and nine nuclear markers recovered a close relationship between P. cyclopsi and the new Plasmodium parasite with the rodent species Plasmodium berghei, a widely used in vivo model to study malaria in humans. The data suggests that the “rodent/bat” Plasmodium (Vinckeia) clade represents a diverse group of malarial parasites that would likely expand with a systematic sampling of small mammals in tropical Africa. Identifying the bat Plasmodium repertoire is central to our understanding of the evolution of Plasmodium parasites in mammals.

Cryptosporidium spp. are important diarrhea-associated pathogens in humans and livestock. Among the known species, Cryptosporidium xiaoi, which causes cryptosporidiosis in sheep and goats, was previously recognized as a genotype of the bovine-specific Cryptosporidium bovis based on their high sequence identity in the ssrRNA gene. However, the lack of genomic data has limited characterization of the genetic differences between the two closely related species. In this study, we sequenced the genomes of two C. xiaoi isolates and performed comparative genomic analysis to identify the sequence uniqueness of this ovine-adapted species compared with other Cryptosporidium spp. Our results showed that C. xiaoi is genetically related to C. bovis as shown by their 95.8% genomic identity and similar gene content. Consistent with this, both C. xiaoi and C. bovis appear to have fewer genes encoding mitochondrial metabolic enzymes and invasion-related protein families. However, they appear to possess several species-specific genes. Further analysis indicates that the sequence differences between these two Cryptosporidium spp. are mainly in 24 highly polymorphic genes, half of which are located in the subtelomeric regions. Some of these subtelomeric genes encode secretory proteins that have undergone positive selection. In addition, the genomes of two C. xiaoi isolates, identified as subtypes XXIIIf and XXIIIh, share 99.9% nucleotide sequence identity, with six highly divergent genes encoding putative secretory proteins. Therefore, these species-specific genes and sequence polymorphism in subtelomeric genes probably contribute to the different host preference of C. xiaoi and C. bovis.

Lactate dehydrogenase (LDH) from Schistosoma mansoni has peculiar properties for a eukaryotic LDH. Schistosomal LDH (SmLDH) isolated from schistosomes, and the recombinantly expressed protein, are strongly inhibited by ATP, which is neutralized by fructose-1,6-bisphosphate (FBP). In the conserved FBP/anion binding site we identified two residues in SmLDH (Val187 and Tyr190) that differ from the conserved residues in LDHs of other eukaryotes, but are identical to conserved residues in FBP-sensitive prokaryotic LDHs. Three-dimensional (3D) models were generated to compare the structure of SmLDH with other LDHs. These models indicated that residues Val187, and especially Tyr190, play a crucial role in the interaction of FBP with the anion pocket of SmLDH. These 3D models of SmLDH are also consistent with a competitive model of SmLDH inhibition in which ATP (inhibitor) and FBP (activator) compete for binding in a well-defined anion pocket. The model of bound ATP predicts a distortion of the nearby key catalytic residue His195, resulting in enzyme inhibition. To investigate a possible physiological role of this allosteric regulation of LDH in schistosomes we made a kinetic model in which the allosteric regulation of the glycolytic enzymes can be varied. The model showed that inhibition of LDH by ATP prevents fermentation to lactate in the free-living stages in water and ensures complete oxidation via the Krebs cycle of the endogenous glycogen reserves. This mechanism of allosteric inhibition by ATP prevents the untimely depletion of these glycogen reserves, the only fuel of the free-living cercariae. Neutralization by FBP of this ATP inhibition of LDH prevents accumulation of glycolytic intermediates when S. mansoni schistosomula are confronted with the sudden large increase in glucose availability upon penetration of the final host. It appears that the LDH of S. mansoni is special and well suited to deal with the variations in glucose availability the parasite encounters during its life cycle.

Key parasite transmission parameters are difficult to obtain from elusive wild animals. For Echinococcus multilocularis, the causative agent of alveolar echinococcosis (AE), the red fox is responsible for most of the environmental contamination in Europe. The identification of individual spreaders of E. multilocularis environmental contamination is crucial to improving our understanding of the ecology of parasite transmission in areas of high endemicity and optimising the effectiveness of prevention and control measures in the field. Genetic faecal sampling appears to be a feasible method to gain information about the faecal deposition of individual animals. We conducted a 4 year faecal sampling study in a village that is highly endemic for E. multilocularis, to assess the feasibility of individual identification and sexing of foxes to describe individual infection patterns. Individual fox identification from faecal samples was performed by obtaining reliable genotypes from 14 microsatellites and one sex locus, coupled with the detection of E. multilocularis DNA, first using captive foxes and then by environmental sampling. From a collection of 386 fox stools collected between 2017 and 2020, tested for the presence of E. multilocularis DNA, 180 were selected and 124 samples were successfully genotyped (68.9%). In total, 45 unique individual foxes were identified and 26 associated with at least one sample which tested positive for E. multilocularis (Em(+)). Estimation of the population size showed the fox population to be between 29 and 34 individuals for a given year and 67 individuals over 4 years. One-third of infected individuals (9/26 Em(+) foxes) deposited 2/3 of the faeces which tested positive for E. multilocularis (36/60 Em(+) stools). Genetic investigation showed a significantly higher average number of multiple stools for females than males, suggesting that the two sexes potentially defecated unequally in the studied area. Three partially overlapping clusters of fox faeces were found, with one cluster concentrating 2/3 of the total E. multilocularis-positive faeces. Based on these findings, we estimated that 12.5 million E. multilocularis eggs were produced during the study period, emphasizing the high contamination level of the environment and the risk of exposure faced by the parasite hosts.

There are several species of gymnophallid digeneans in the genus Parvatrema that are unique in developing metacercariae that reproduce by parthenogenesis in the second intermediate host. Transmission of these digeneans takes place in coastal ecosystems of the North Pacific and North Atlantic seas. The first intermediate hosts are bivalves, the second ones are gastropods, and the definitive hosts are migratory birds. We integrated data accumulated over 25 years of research and differentiated a complex of five closely related species. They differ in the molluscan second intermediate hosts, distribution ranges, and life cycles patterns. The type I life cycle includes two generations of parthenogenetic metacercariae, followed by development of metacercariae which are invasive for the definitive host. In the type II life cycle, the number of generations of parthenogenetic metacercariae is unlimited, and they can also produce cercariae. These cercariae emerge into the environment and can infect new individuals of the second intermediate host. We conclude that the type I life cycle is a derived option that has evolved as a better fit to transmission in the unstable conditions in the intertidal zone. Another evolutionary trend in Parvatrema is transition from inhabiting the extrapallial space of the gastropod second intermediate host to endoparasitism in its mantle and internal organs. rDNA sequence analysis highlighted that Parvatrema spp. with parthenogenetic metacercariae form a monophyletic clade and suggested the Pacific origin of the group, with two transfers to the North Atlantic and colonisation of new second intermediate host species. Apparently the group formed in the late Pliocene-Pleistocene and diversified as a result of recurrent isolation in inshore refugia during glacial periods. We argue that parthenogenetic metacercariae in Parvatrema may serve as a model for early digenean evolution, demonstrating the first steps of adopting the molluscan first intermediate host and becoming tissue parasites.

Parasites are a key driving force behind many ecological and evolutionary processes. Prevalence and diversity of parasites, as well as their effects on hosts, are not uniform across host species. As such, the potential parasite spillover between species can significantly influence outcomes of interspecific interactions. We screened two species of Luscinia nightingales for haemosporidian blood parasites (Plasmodium, Leucocytozoon and Haemoproteus) along an approximately 3000 km transect in Europe, incorporating areas of host distant allopatry, close allopatry and sympatry. We found significant differences in infection rates between the two host species, with common nightingales having much lower parasite prevalence than thrush nightingales (36.7% versus 83.8%). This disparity was mostly driven by Haemoproteus prevalence, which was significantly higher in thrush nightingales while common nightingales had a small, but significantly higher, Plasmodium prevalence. Furthermore, we found no effect of proximity to the contact zone on infection rate in either host species. Despite having lower infection prevalence, common nightingales were infected with a significantly higher diversity of parasite lineages than thrush nightingales, and lineage assemblages differed considerably between the two species, even in sympatry. This pattern was mostly driven by the large diversity of comparatively rare lineages, while the most abundant lineages were shared between the two host species. This suggests that, despite the close evolutionary relationships between the two nightingales, there are significant differences in parasite prevalence and diversity, regardless of the distance from the contact zone. This suggests that spillover of haemosporidian blood parasites is unlikely to contribute towards interspecific interactions in this system.

Trichomonas vaginalis is a medically important protozoan parasite, and a deep-branching, evolutionarily divergent unicellular eukaryote that has conserved several key features of eukaryotic gene expression. Trichomonas vaginalis possesses a metazoan/plant-like capping apparatus, mRNAs with a cap 1 structure and spliceosomes containing the five small nuclear RNAs (snRNAs). However, in contrast to metazoan and plant snRNAs, the structurally conserved T. vaginalis snRNAs were initially identified as lacking the canonical guanosine cap nucleotide. To explain this unusual condition, we sought to investigate transcriptional and processing features of the spliceosomal snRNAs in this protist. Here, we show that T. vaginalis spliceosomal snRNA genes mostly lack typical eukaryotic promoters. In contrast to other eukaryotes, the putative TATA box in the T. vaginalis U6 snRNA gene was found to be dispensable for transcription or RNA polymerase selectivity. Moreover, U6 transcription in T. vaginalis was virtually insensitive to tagetitoxin compared with other cellular transcripts produced by the same RNA polymerase III. Most important and unexpected, snRNA transcription in T. vaginalis appears to bypass capping as we show that these transcripts retain their original 5′-triphosphate groups. In conclusion, transcription and processing of spliceosomal snRNAs in T. vaginalis deviate considerably from the conventional rules of other eukaryotes.

Pleustonic organisms form an important part of pelagic ecosystems by contributing to pelagic trophic chains and supporting connectivity between oceanic habitats. This study systematically analysed the trematode community harboured by pleustonic molluscs and cnidarians from offshore Queensland, Australia. Four mollusc and three cnidarian species were collected from beaches of North Stradbroke Island, Queensland. Two mollusc species and all three cnidarians harboured large numbers of hemiuroid metacercariae (Trematoda: Hemiuroidea). Eight taxa from four hemiuroid families (Accacoeliidae, Didymozoidae, Hemiuridae and Sclerodistomidae) were distinguished via molecular sequencing. Four of those taxa were identified to species. All trematode taxa except one didymozoid were shared by two or more host species; five species occurred in both gastropods and cnidarians. It is hypothesised that the life-cycles of these hemiuroids are highly plastic, involving multiple opportunistic pathways of metacercarial transmission to the definitive hosts. Transmission and the use of pleuston by hemiuroids likely varies with sea surface use and ontogenetic trophic shifts of apex predators. The small number of trematode species found in pleuston is consistent with significant ecological specificity, and the inference that other pelagic trematodes use alternative pathways of transmission that do not involve pleustonic organisms. Such pathways may involve i) pelagic hosts exclusively; ii) benthic or demersal hosts exclusively, consumed by apex predators during their dives; or iii) both benthic and pelagic hosts in transmission chains dependent on vertical migrations of prey. The influence of the connectivity of open-ocean ecosystems on parasite transmission is identified as an area in critical need of research.