International journal for parasitology最新文献

Parvicapsula pseudobranchicola is a marine myxozoan parasite of high significance to Atlantic salmon (Salmo salar) aquaculture, particularly in northern regions such as Norway and Iceland, where outbreaks have been reported with increasing frequency and severity in recent years. In this study, we aim to resolve the life cycle of P. pseudobranchicola by screening benthic invertebrate communities in areas with known infection pressure in salmon farms as well as performing a transmission trial using post-smolt Atlantic salmon and polychaetes. Sediment samples were collected using a Van Veen grab sampler, covering a 0.025 m² area at each sample site. Polychaetes found were subjected to microscopic investigation, PCR, Sanger sequencing, histology and in situ hybridization. Fish were challenged with actinospores using two different methods. The polychaete Chaetozone setosa was identified as the definitive host of P. pseudobranchicola. Actinospores of morphotype saccimyxon, measuring 5-6 µm in diameter are described. Each spore contained three spherical polar capsules, approximately 0.7-1.0 µm in diameter. Four of the 20 challenged fish (20%) tested positive for parasite DNA in blood samples by PCR. By identifying and confirming the polychaete Chaetozone setosa as the definitive host of Parvicapsula pseudobranchicola, we resolve the sixth known marine myxozoan life cycle. These results provide immediate utility. Life cycle resolution enables targeted surveillance and site-specific risk zoning as mitigation for parvicapsulosis, that should reduce impact on fish welfare and losses from the disease.

Echinococcus multilocularis is a parasitic tapeworm responsible for alveolar echinococcosis (AE), a life-threatening zoonotic disease. Understanding its genetic diversity and historical spread is critical for developing effective control measures. Previous studies have suggested Central Asia as a potential origin of the parasite, but comprehensive global analyses encompassing multiple regions and time periods have been limited. This study aimed to analyze the genetic diversity, population structure, and phylogeography of E. multilocularis by sequencing the complete mitogenome from 384 isolates from major endemic regions across the Northern Hemisphere. We sequenced 201 new E. multilocularis mitogenomes and combined these with 183 previously published sequences. Phylogenetic, haplotype network, pairwise fixation index (Fst), and principal-component analysis (PCA) were performed to explore genetic diversity, population structure, and the historical spread of the parasite. Bayesian phylogeographic reconstruction was used to infer diffusion routes across the Northern Hemisphere. Our analysis identified five major clades, with high genetic diversity observed in samples from China-Xinjiang and China-Midwest. The parasite exhibited significant genetic differentiation between continents, with most clades tracing their origins to Central Asia. Phylogeographic analysis suggested that E. multilocularis spread from Central Asia to Europe, Japan, and North America, primarily through wildlife migration and human activities. This study supports the hypothesis that Central Asia is the evolutionary origin of E. multilocularis and provides insights into its historical and contemporary dispersal patterns. The findings highlight the importance of monitoring and controlling the spread of human AE, particularly in regions, with high genetic diversity, to prevent further spread.

Parasite infections in host populations frequently display seasonal patterns that can shape host behavior, fitness, and population dynamics. Despite recognition that seasonality plays a key role in infection dynamics across numerous host-parasite systems, the drivers of seasonal infection dynamics for parasites with different life cycles are often unknown. This lack of system-specific understanding restricts our ability to predict when and why parasite infections and their cascading effects on host populations will have the greatest impact. We investigated how seasonality and environmental variables at the likely time of infection are related to the infection intensity of two parasitic nematodes with contrasting life cycles: strongyle nematodes (direct life cycle) and lungworms (indirect life cycle). We conducted the study in two free-ranging ungulate species in Serengeti National Park, Tanzania: Coke's hartebeest (Alcelaphus buselaphus) and topi (Damaliscus lunatus). We found a high prevalence of both parasites, with strongyle nematodes occurring in 95.5% of hartebeest and 93.1% of topi, and lungworms occurring in 100% of hartebeest and 99.7% of topi. Strongyle infection intensity peaked in the wet season but showed no strong association with precipitation, temperature, or animal density at the likely time of infection. In contrast, lungworm intensity peaked in the dry season and was associated negatively with precipitation and positively with animal occupancy. Our results highlight the importance of considering how parasite life cycles interact with environmental variables operating at different temporal scales, as seasonal infection patterns may emerge from processes acting at distinct times relative to parasite development and transmission. Identifying when parasite intensities are highest is critical for predicting when hosts are under the greatest ecological pressure due to parasitism.

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.