International journal for parasitology最新文献

The likelihood of infection is influenced by both innate and environmental factors, including host defences and contacts with infectious stages. Although theory predicts that motile parasites ought to select susceptible host species, few studies have considered parasite preference among individuals of a single host species. By experimentally manipulating the presence, activity, and susceptibility of tadpoles, we tested the importance of host cues (chemical and mechanical) and host resistance on intraspecific host choice by free-swimming trematode (flatworm) cercariae. Cercariae could 'choose' among four chambers with these combinations in a first set of trials but could not contact (and infect) hosts. In a second set of trials with the same tadpoles, cercariae were allowed to select and infect hosts, allowing us to analyze the relationship between initial parasite choice and subsequent infection establishment. Cercariae showed a trend for greater attraction to anesthetized tadpoles over negative controls (empty chambers), suggesting the use of chemical cues to locate hosts, but were most attracted to active (non-anesthetized) tadpoles, indicating an important role for host movement. Cercariae showed no preference for tadpoles subjected to an immunosuppressive treatment, despite their greater susceptibility to infection. Importantly, the initial number of cercariae that chose each tadpole in the first round positively predicted parasite load in the second round of exposures. Highly active hosts, which initially attracted the most cercariae, ultimately supported the highest infections, either because parasites made 'good' host choices, or, alternatively, prior host exposure (without actual infection) increased susceptibility.

Neospora caninum is an apicomplexan parasite responsible for bovine neosporosis, a leading cause of abortion and economic loss in cattle worldwide. Despite its veterinary significance, the molecular mechanisms underlying parasite virulence and host-pathogen interaction remain poorly understood. In particular, the contribution of rhoptry proteins, key secretory effectors involved in host cell invasion and immune modulation, has yet to be fully elucidated. Here, we investigate NcROP24, a previously understudied rhoptry protein whose expression correlates with isolate virulence. Using CRISPR/Cas9, we generated NcROP24 knock-out mutants (NcΔROP24) by deleting all three genomic copies and confirmed loss of expression with a single-copy insertion of a selectable marker DHFR-TS. In a pregnant mouse model, NcΔROP24 parasites displayed markedly reduced congenital transmission, higher neonatal survival, and lower maternal brain parasite burdens compared to wild-type controls, demonstrating significant attenuation of systemic and vertical infection. Also, in bovine monocyte-derived macrophages, NcΔROP24 tachyzoites showed impaired intracellular growth. Dual RNA-seq of infected macrophages revealed that NcΔROP24 loss prevents the parasite from reprogramming key host metabolic and degradative pathways, instead promoting a stress-induced, lipogenic state that favours clearance. Concurrently, parasites lacking NcROP24 upregulated stress-associated transcripts and downregulated additional secreted effectors, indicating a shift away from aggressive proliferation. Together, these findings establish NcROP24 as a key factor of N. caninum pathogenicity. By defining its role in host-pathogen interactions, our work highlights NcROP24 as a promising target for next-generation vaccines or therapeutics against bovine neosporosis.

Parasites are ubiquitous and exert varied ecological and evolutionary pressures on their hosts. Yet, characterising parasite diversity and distributions can be challenging and costly. Leveraging existing data to identify parasites is thus an attractive alternative. High-throughput sequencing (HTS) can generate whole genome sequence (WGS) data which are increasingly freely available in public repositories and represent an untapped resource for characterising parasites affiliated with hosts. In this study, we examine WGS data generated for the silvereye (Zosterops lateralis), to identify endogenous eukaryotic parasites that were inadvertently captured during host sequencing. We compared detection of parasite genera by this approach with detection via 18S metabarcoding. Mining WGS data for parasite DNA revealed the broadest range of genera. Results were verified by traditional microscopy of blood slides and conducting a targeted multiplex Polymerase Chain Reaction (PCR) for haemosporidian parasites. Detection of haemosporidians was largely consistent across microscopy, multiplex PCR and WGS data while 18S metabarcoding entirely failed to detect this group of parasites. Our results demonstrate that existing WGS datasets can be used to estimate endoparasite diversity and provide greater insights on diversity than metabarcoding whilst also avoiding the costs and challenges of direct sampling. We provide a framework outlining opportunities and constraints to consider when mining WGS data to identify parasite sequences. The framework particularly stresses the influences of sequencing depth, database completeness, and methodological biases. Our findings demonstrate how repurposing existing WGS data can provide a cost-effective and informative means of unravelling complex host-parasite interactions in future disease ecology studies.

Leishmania infantum is an intracellular protozoan parasite that causes visceral leishmaniasis, predominantly affecting marginalized populations in tropical and subtropical countries. The parasite genome comprises 36 chromosomes whose ends have not been characterized. In most eukaryotes, chromosome termini are capped by telomeres and associated proteins, forming nucleoprotein structures that maintain genome stability and prevent the ends from being mistaken as broken DNA. Leishmania telomeres are composed of G-rich repetitive DNA replenished by telomerase activity. Here, we showed a detailed view and assessment of the 72 chromosome end termini of L. infantum reference strain JPCM5 using Southern blot and Oxford nanopore (ONT) whole genome sequence. L. infantum telomeres, besides the canonical hexameric repeat, contain hexamer variants. The subtelomeres comprise frequent octameric repeats intercalated by interstitial telomeric hexamers and a 62 bp Leishmania conserved telomere-associated sequence containing the Conserved Sequence Block 2 (CSB2) and other elements. The ONT data also provided a complete panorama of L. infantum chromosome termini, showing clusters of high gene density, and determining the telomere size in all chromosome arms. The estimated L. infantum TRF (terminal restriction fragment) length, ranging from 100 to 500 bp, is sensitive to T5 exonuclease digestion, confirming they are at the termini; a similar strategy was used to assess the subtelomeric octameric repeats. Also, procyclic and metacyclic promastigotes showed similar TRF profiles, and promastigote telomeres show different nuclear distributions depending on the cell cycle phase. Our results showed that L. infantum chromosome ends show a mosaic organization, adding valuable information about its genomic architecture and evolution.

Honey bees are recognised as the primary pollinators of most agricultural crops and numerous wild plant species worldwide. However, the colony losses reported over recent decades pose a serious threat to this essential ecosystem service. The spread of pathogens has been identified as a significant factor contributing to the decline of honey bee populations. Consequently, there is a considerable interest in expanding our knowledge on the prevalence of emerging pathogens on honey bee colonies, particularly trypanosomatids and neogregarines. Herein, we conducted a spatio-temporal analysis of the prevalence of trypanosomatids (Lotmaria passim and Crithidia mellificae) and a neogregarine (Apicystis bombi) in honey bee populations across the Canary Islands sampled over a 20-year period (1998-2017). We also examined whether pathogen prevalence was associated with the introduction of foreign honey bee queens to the islands and the implementation of a conservation programme of the local Canarian black honey bee. Our results indicate that L. passim has been present in the Canary Islands since at least 1998, whereas C. mellificae was not detected. This finding represents the earliest known global record of the L. passim worldwide. Apicystis bombi was found on several islands during the study period, though at low frequency. The prevalence of L. passim did not exhibit any correlation with the introduction of foreign honey bee queens, unlike other pathogens and parasites such as Nosema ceranae and Varroa destructor. Notably, the implementation of long-standing conservation measures in La Palma was associated with a higher prevalence of L. passim compared to Gran Canaria. These results suggest that L. passim may have been present in the Canary Islands prior to the introduction of foreign honey bees in recent decades. Further analyses of historical samples from additional regions, particularly from geographically isolated areas such as islands, are necessary to untangle the spread history of L. passim in honey bee populations.

Ascaridia galli (A. galli), a parasitic roundworm that infects chickens poses an economic burden in poultry farming, as it causes ascaridiosis-a disease leading to reduced growth, lower egg production, and immunosuppression. Recently, interest has grown in the parasite's extracellular vesicles (EVs), as they modulate host immune responses and play a key role in host-pathogen interactions. This study aimed to optimize in vitro EV-production from A. galli and assess their uptake by chicken immune cells important for EV mediated host-pathogen communication. Adult worms were collected from infected chickens, sex-sorted, washed, and cultured in vitro. EVs were isolated at various time points using size exclusion chromatography and characterized. DiO-stained EVs were evaluated for uptake into chicken intestinal epithelial cells, macrophages, peripheral blood mononuclear cells and whole blood leukocytes using flow cytometry and confocal microscopy after 4 and 24 h incubation with the parasite derived vesicles. EV-uptake increased significantly from 4 h to 24 h across all tested cell types. Female-derived EVs collected after 24 h of worm culture gave rise to higher uptake than male-derived EVs. However, at the 40 h time point, male EVs gave rise to greater uptake, though overall EV internalization was reduced compared to the 24 h time point. Uptake efficiency varied depending on the EV collection time as well as the host cell type. These findings suggest that both the sex of the worm and the duration of culture influence EV uptake, with 24 h emerging as the optimal in vitro culture duration for production of A. galli derived EVs with potent biological functions. The sex-specific differences highlight potential functional diversity in EV mediated host-pathogen interactions, which need to be assessed in future studies.

Mitochondrial genomes of apicomplexan parasites exhibit remarkable structural diversity, ranging from highly reduced linear molecules to circular-mapping concatemers, yet their full characterization has been hindered by technical limitations in resolving complex infections. This study establishes a novel integrated workflow combining one-step PCR amplification with Oxford Nanopore Technologies (ONT) to sequence complete mitochondrial genomes from Eimeriidae and Haemosporida parasites. Successful assembly of 29 high-quality mitogenomes (12 Eimeriidae, 17 Haemosporida) from 15 samples, demonstrating the method's sensitivity. Comparative analyses revealed cryptic mixed/co-infections in 11 samples that were undetectable by Sanger sequencing, highlighting ONT's superior resolution for uncovering true parasite diversity. Phylogenomic reconstruction using the largest Eimeriidae dataset to date confirmed the monophyly of passeriform Isospora and identified a basal position for a novel Caryospora lineage from Ptyas major. In Haemosporida, analysis of 202 mitogenomes revealed non-monophyletic familial relationships. Selection analyses indicated predominant purifying selection in mitochondrial protein-coding genes of Eimeriidae. Our findings underscore the utility of long-read mitogenomics in elucidating complex infection dynamics and provide a scalable framework for biodiversity surveys of understudied apicomplexans parasites, with implications for understanding their evolutionary ecology and host-parasite interactions.

Early identification of people at risk of schistosomiasis infection is critical to interrupting disease transmission. We develop and validate an explainable machine learning prediction model that integrates demographic, behavioral, and environmental factors to identify these individuals. A total of 103,707 individuals were included to train and internally validate the model, and 16,574 individuals were used for external validation. The Random Forest (RF) model demonstrated the best discriminative performance among the five machine learning models evaluated. It accurately predicted schistosomiasis seropositivity in both internal validation (AUC = 0.943, F1 score = 0.809) and external validation (AUC = 0.897, F1 score = 0.770) and has been translated into a practical tool to support real-world application. Feature importance analysis indicated that the most significant predictors of schistosomiasis seropositivity included the presence of schistosomiasis symptoms, history of exposure to infected water, endemicity types of the village, gender, and village risk category. Furthermore, the SHapley Additive exPlanation (SHAP) method was employed to explain how these variables influence the prediction outcomes. This study provides a reference for early identification of high-risk populations and facilitates the translation of theoretical modeling studies into practical work applications.

Heterozygosity-fitness correlations (HFCs) are widely used to explore the effects of inbreeding in wild populations. However, the biological significance of HFCs has been the subject of intense debate, and it has been suggested that the magnitude and direction of these correlations may be context-dependent (e.g., vary with different host characteristics or environmental conditions). We tested this hypothesis in a free-ranging population of Grant's gazelles (Nanger granti). Specifically, we tested for associations between standardized multilocus heterozygosity (sMLH) and endoparasite infections, and examined how these relationships varied with animal age, sex and environmental context (e.g., seasonality). We did this using three approaches: a cross-sectional approach focusing on 103 individuals sampled at a single time point, a longitudinal approach focusing on 25 naturally infected individuals sampled over 12 months, and an experimental approach in which 15 individuals were cleared of their parasites and parasite re-accumulation was tracked over 12 months. We found that the presence of heterozygosity-parasite associations varied with study design and context. Cross-sectional patterns varied with environmental context, whereas the longitudinal analysis revealed trait-specific HFCs, and the experiment established a causal link between heterozygosity and parasitism. Overall, our longer-term study approaches indicated that higher levels of heterozygosity are associated with lower parasite burdens, underscoring the value of longitudinal and experimental approaches for detecting HFCs in wild populations.

The potential of natural history collections to address biological questions has been increasingly recognized with the advent of high-throughput sequencing (HTS) and museomics approaches. However, their use remains largely underexplored for most taxonomic groups. This is particularly true for proteocephalid cestodes (Onchoproteocephalidea I), for which extensive material is available in helminthological collections. Here, we subjected ethanol-preserved specimens deposited in two helminthological collections to HTS using a genome skimming approach. This allowed us to recover dozens of mitogenomes and nuclear ribosomal transcription units (rTUs) and to place them within a phylogenetic framework. We generated 88 complete or partial mitogenomes and rTUs. These samples correspond to 78 species in 43 genera from all continents except Antarctica, including parasites of fishes (86 %), snakes, monitor lizards, and the common opossum. Comparative analyses revealed highly conserved mitochondrial content and architecture, following the typical pattern recognized for proteocephalid cestodes. Phylogenetic reconstructions based on concatenated mitogenomes and rTUs datasets were largely concordant with the most comprehensive phylogenies published to date, with several informal clades also recognized in this study: the "Proteocephalus-aggregate", the "African fish clade", Clade K of the "cosmopolitan reptilian clade", and the "Neotropical fish superclade". However, improved resolution was obtained in the parsimony analyses for early-diverging lineages represented by Old World cestodes of the subfamilies Acanthotaeniinae and Gangesiinae. Also, we identified the MT-ND5 gene as the most informative under the parsimony criterion, whereas the most frequently sampled MT-CO1 proved far less phylogenetically informative. The data generated here provide a solid foundation for future multilocus phylogenetic and comparative studies of cestodes and highlight the value of genome skimming using decades-old archived samples. New avenues for exploring the evolutionary history of proteocephalid cestodes are discussed.