The protozoan parasite Perkinsus olseni actively proliferates within marine molluscan hosts and causes serious negative effects on mollusk production worldwide. Recent research revealed that one Japanese isolate requires exogenous glycine betaine (GB) for vegetative proliferation, whereas isolates from some congeneric species do not, suggesting that this requirement is a derived characteristic of this genus. In the present study, we established various isolates from Japan, Europe, and Oceania, and showed that P. olseni isolates from Japan and Europe commonly require exogenous GB, whereas Oceanian isolates do not. This suggests that Oceanian isolates may retain ancestral-like characteristics compared to Japanese and European isolates. Analyses of the non-transcribed spacer region of ribosomal DNA further support the above interpretation that the Oceanian isolates represent a more basal split, and additionally suggest that the Japanese and European isolates belong to lineages that have undergone relatively recent geographic expansion. Morphological comparisons among isolates showed that the Oceanian isolates possessed larger schizonts and trophozoites, producing fewer daughter cells, but formed larger hypnospores capable of producing a greater number of zoospores, although the association between GB requirements and morphological differences remains unknown. The present study demonstrates the existence of distinct lineages of this parasite and provides novel insights into the evolution, geographical dispersion, and shifts in life-history strategies of P. olseni.
Infectious diseases are a powerful ecological force, yet the predictors shaping variation in parasite prevalence across wildlife remain incompletely understood. Birds provide an exceptional system to address this challenge, as their global diversity, ecological breadth, and role as pathogen reservoirs make them excellent models for studying infection dynamics. Among avian parasites, haemosporidians (Plasmodium,Haemoproteus, andHaemoproteus subgenus Parahaemoproteus) are nearly ubiquitous, affecting host physiology and survival while offering a model for testing how ecological and evolutionary factors modulate infection risk. Using a georeferenced global dataset of haemosporidian infection, we evaluated how latitude, bird host abundance, bird habitat specialization, bird species age, and parasite co-occurrence influence infection prevalence across avian communities. Bayesian phylogenetic logistic models revealed that these predictors capture key variation in infection patterns.Latitude emerged as the strongest predictor among ecological and evolutionary variables considered, showing contrasting associations across parasite groups: prevalence decreased with latitude for Plasmodium and Haemoproteus, but increased for Parahaemoproteus. Associations among parasite groups also emerged as important predictors of prevalence. Plasmodium prevalence was negatively associated with the prevalence of both Haemoproteus and Parahaemoproteus, while Parahaemoproteus prevalence was negatively associated with Plasmodium prevalence. In contrast, Haemoproteus prevalence was not significantly associated with the occurrence of either Plasmodium or Parahaemoproteus. Abundance and habitat breadth of avian hosts were not meaningfully associated with prevalence in any of the three parasite groups. Similarly, bird species age showed no supported association with parasite prevalence, suggesting that contemporary ecological and geographic factors and interactions among parasite groups are more important than host evolutionary age in explaining global variation in avian haemosporidian prevalence. Collectively, these results demonstrate that incorporating cross-parasite associations within a phylogenetic framework provides new insights into the mechanisms structuring global spatial patterns of haemosporidian prevalence.
Monogenean parasites are among the most common ectoparasites of marine fishes and can influence host health, fitness, and population dynamics. Despite their ecological importance, historical data on monogenean prevalence and diversity in marine fish are scarce. Here, we report data from a historical survey of 1,518 fish, representing 242 species across 87 families, collected from the Central California coast to the Gulf of California between 1967 and 1980. Monogeneans were identified from gills, skin, and body openings, and prevalence and mean abundance were analyzed across five depth zones: sub-littoral, epipelagic, mesopelagic, bathypelagic, and bathyal. Infections were concentrated in sub-littoral and epipelagic fishes, with prevalence and diversity declining in deeper habitats, likely reflecting host density, environmental conditions, and parasite life history. A total of 42 monogenean species from 14 families were recorded, including several undescribed taxa. This historical dataset provides a rare baseline for Pacific marine fishes and offers a valuable reference for assessing long-term changes in parasite populations and host-parasite dynamics under environmental change.
The polymerase chain reaction (PCR) is widely used to amplify malaria parasite DNA to diagnose Plasmodium infections, but can generate artefactual chimeric sequences through template switching. Here, we examine the occurrence and consequences of PCR-generated chimeras in studies of malaria parasites from humans, macaques and mosquitoes, and highlight two major sources of errors. First, in samples containing mixed-species infections, PCR can produce interspecific chimeras. This problem is particularly acute among closely related species of Plasmodium that infect macaques in southeast Asia, several of which have been transmitted to humans. Reanalysis of published mitochondrial DNA sequences from Thailand and Malaysia revealed numerous chimeric sequences involving P. knowlesi, P. inui, and P. cynomolgi, as well as P. vivax and other related species. Second, amplification of multicopy genes can also generate intra-genomic chimeras. The most widely used PCR template for malaria parasite identification has been the small subunit (18S) ribosomal RNA gene, but Plasmodium genomes contain two divergent forms of the rRNA unit, the A-type and the S-type. We show that several studies have generated intertype rRNA chimeras, which can occur even in the absence of multi-species infection. This has led to difficulties in identifying the relevant species, given an inflated view of sequence diversity, and has confused conclusions regarding zoonotic transmissions. These findings highlight the need for more rigorous approaches to PCR amplification to avoid the generation of chimeras, and for the validation of potentially chimeric sequences before phylogenetic or epidemiological interpretation.
The cumulative number of parasite species known to science keeps increasing steadily year after year, suggesting we are far from the end of our inventory of extant parasite biodiversity. However, what about higher taxa such as genera or families: are their known numbers also still rising? Finding new genera or families represents the discovery of clades with greater evolutionary uniqueness than the discovery of new species belonging to already known lineages. We surveyed the taxonomic literature between 2010 and 2025 to quantify patterns in the discovery of new helminth genera and families. Few new families were proposed during the study period, however 271 new genera were established, with 80% of them being 'true' new genera, i.e. previously unknown lineages based entirely on the discovery of new specimens. Whereas we might expect that the more genera one has already found, the harder it could be to find new ones, we instead found a positive relationship between the number of new genera found per higher taxon and the currently known species richness of that taxon. This supports a sampling hypothesis whereby species-rich taxa like Trematoda are also the ones likely to yield more new genera. Indeed, the cumulative number of new trematode genera found in the 2010-2025 period has increased linearly, suggesting many more genera await discovery in this taxon as well as in Nematoda, Monopisthocotylea and Polyopisthocotylea. In contrast, an asymptote has been reached in Acanthocephala and Cestoda, indicating the final list of genera is at hand in those taxa. Our findings suggest that the quest to document parasite biodiversity is far from complete as we still lack knowledge of many phylogenetically distinct helminths characterised by morphologies that do not fit within currently known genera.
Parasitic flatworms, including cestodes and trematodes, are covered by a specialized syncytial tegument that mediates nutrient uptake and host-parasite interactions. While the tegument of trematodes has been extensively characterized, its molecular composition in cestodes remains largely unknown. In this work, we performed a comparative proteomic analysis of the tegument of three cestode species, including larval and adult stages: Hymenolepis microstoma, Mesocestoides corti (syn. M. vogae) and the human pathogen Echinococcus multilocularis. Using stringent enrichment criteria relative to whole-worm extracts, we identified hundreds of tegument-enriched proteins in each species. Comparative analyses revealed a conserved core of tegumental proteins shared among all three species, including members of the Tegument Allergen-Like (TAL) family, vesicular trafficking components and calcium-sensing proteins, and identified candidates for nutrient uptake activities such as glucose and nucleoside transporters. Further comparative analyses revealed a set of shared tegumental proteins with the trematode Schistosoma mansoni, including conserved proteins that are specific to parasitic flatworms, supporting the existence of a conserved ancestral tegumental proteome. Finally, we confirmed tegumental expression of several genes in H. microstoma and E. multilocularis, and demonstrated regionally restricted gene expression among tegumental cytons, suggesting functional specialization within the syncytial tegument. Altogether, these results reveal an evolutionarily conserved composition of the tegument of parasitic flatworms, providing a foundation for future work targeting this critical host-parasite interface.
Biomphalaria snails are intermediate hosts of Schistosoma mansoni, and their distribution predicts where intestinal schistosomiasis may occur. Here, we investigated the genetic diversity and distribution patterns of Biomphalaria spp. in the Lake Albert region and assessed their role in the transmission of schistosomes. Snails (n = 6869) were screened for schistosome infections using cercariae shedding and molecular techniques. In total, 29,670 Biomphalaria snails were collected, 90% of which were in the upland sites. For a subset of snails (n = 184) we sequenced a partial cytochrome c oxidase subunit one (COX1) fragment for phylogeographic analyses. Biomphalaria sudanica, Biomphalaria pfeifferi and Biomphalaria stanleyi were identified, with the former two species having haplotypes shared at the lake and upland sites. We also report the presence of a cryptic lineage, tentatively named B. cf. pfeifferi, awaiting further description. Molecular assays revealed higher overall prevalence of S. mansoni (1.9%) and S. rodhaini (1.12%) among Biomphalaria spp. (n = 1619) than inferred from cercarial shedding (0.66%). However, S. mansoni occurred exclusively at lake and nearby stream sites and was hosted predominantly by B. sudanica (24.7%, 22/89) and B. pfeifferi (5.4%; 5/147), while S. rodhaini, hosted mainly by B. cf. pfeifferi, was widely distribution in upland sites allopatric to S. mansoni. The wet season (October and November) had the highest S. mansoni prevalence. We argue that the lack of S. mansoni in upland sites reflects a more nuanced situation than simply the absence of suitable host snails, and suggest taxonomic revision of the B. pfeifferi complex.
Hyperparasitism, in which a parasite exploits another parasite, represents a logical extension of parasite diversity and complexity within ecological networks. While common and ecologically significant in microbial systems, hyperparasitism among metazoan parasites appears comparatively rare. This discrepancy is intriguing given the high diversity and frequent co-occurrence of parasites within hosts. Here, we compile and review published cases of hyperparasitism involving metazoan parasites to assess their taxonomic distribution and ecological characteristics. We identify a wide range of hyperparasitic strategies, including opportunistic associations and highly specialized interactions. However, many published cases appear to be accidental or rare, suggesting that true hyperparasitism is even less frequent than reported. We argue that the relative rarity of hyperparasitism among metazoan parasites results from a combination of ecological and evolutionary constraints, including low encounter probabilities, dependence on multiple hosts, parasite aggregation, limited trophic accessibility, structural simplicity of parasite bodies, the presence of dual immune barriers imposed by both host and parasite, and, especially, energetic scaling constraints. Together, these factors restrict the conditions under which hyperparasitism can evolve and persist. Therefore, despite the vast diversity of parasites, their suitability as hosts is limited, and thus they rarely serve as hosts for other metazoan parasites. In this context, "good parasites" may indeed make "bad hosts."
Anthropogenic climate change is expected to increase not only mean temperatures but also the magnitude and pattern of thermal variability, including the frequency, duration, and predictability of extreme events. While the effects of elevated mean temperatures on disease dynamics are well studied, far less is known about how different patterns of temperature variability shape host-parasite interactions, despite theoretical predictions from the climate variability hypothesis. Here, we used a controlled experimental system (Daphnia magna and two microsporidian parasites, Ordospora colligata and Hamiltosporidium tvaerminnensis) to disentangle the effects of thermal variability. Across two experiments conducted under different thermal regimes, we exposed hosts to cyclic (predictable) and random (unpredictable) heatwaves. Contrary to predictions from the climate variability hypothesis, temperature variability did not uniformly increase infection risk. Instead, infection outcomes depended on the mean temperature, duration of the heatwaves, the pattern of thermal variation, and parasite identity. At lower temperatures (Experiment 1), thermal variability had minimal effects on infection. At higher mean temperatures (Experiment 2), parasites responded in distinct ways: H. tvaerminnensis spore production was sensitive to the pattern of heat events, whereas O. colligata responded primarily to heatwave duration. These results demonstrate that climatic variability can differentially alter host-parasite interactions rather than exerting consistent directional effects on disease, with the effects of temperature variability depending on both species identity and thermal regime. Taken together, these findings suggest that increasing climatic variability may influence parasite communities and disease outcomes under the ongoing global change.
Calicophoron daubneyi is an emerging rumen fluke of ruminants whose prevalence and geographic range have increased markedly across Western Europe over recent decades. Despite its growing veterinary importance, population-level genetic studies of this trematode have been hampered by the absence of suitable multilocus markers, with previous work relying on mitochondrial or ribosomal sequences that provide limited resolution for epidemiological inference. In this study, we developed and validated the first panel of polymorphic microsatellite markers for C. daubneyi and applied them to assess genetic diversity, clonality, and population structure in natural populations from the eastern French Pyrenees. Using Illumina-based genomic sequencing, we isolated 16 candidate loci, of which 10 robust and polymorphic microsatellites were retained after stringent quality filtering. We used these markers to genotype 187 adult parasites collected from cattle originating from seven localities spanning a maximum pairwise distance of approximately 50 km. Analyses explicitly accounted for the strong clonal amplification characteristic of trematode life cycles. We observed high levels of genetic diversity and a pronounced but variable clonal signal among sites. After attempting to correct for clonality and null alleles, genetic differentiation among populations was low and no significant isolation by distance was detected, consistent with substantial genetic exchange occurring at the regional spatial scale examined. These findings suggest that definitive host movement contributes importantly in shaping parasite gene flow within this interconnected livestock system. By providing the first validated microsatellite toolkit and baseline population-genetic data for C. daubneyi, this study establishes a foundation for future molecular epidemiological investigations of transmission dynamics, host-parasite interactions, and parasite dispersal in European livestock systems.
African protected areas support exceptional wildlife diversity, yet their parasite diversity remains poorly characterised. Documenting parasite biodiversity is increasingly urgent as global change alters species distributions and threatens to cause mass parasite extinctions. Digenean trematodes are thought to be particularly sensitive to environmental stressors due to their complex life cycles, involving gastropod intermediate hosts and a wide range of secondary and definitive hosts. This study used a metabarcoding approach targeting the nuclear 28S rDNA region with the aim of characterising trematode communities within freshwater snail hosts from two southern African protected areas: Kruger National Park, (KNP), South Africa and Bwabwata National Park (BNP), Namibia. Additionally, patterns of alpha diversity and trematode co-infection across snail species were assessed within both parks. Metabarcoding revealed high trematode diversity and co-infection rates in snail hosts, detecting species of veterinary (Schistosoma mattheei, Fasciola gigantica) and conservation (Riberioa cf. ondatrae) importance, across different snail species in both parks. The invasive snail Tarebia granifera in KNP showed significantly higher trematode richness compared to all other snail species, with all sampled individuals showing co-infection. Metabarcoding is a promising tool for assessing parasite diversity and within host communities, although there is an urgent need for improved trematode molecular reference databases. This work has important implications for biodiversity management, veterinary health and public health surveillance in African wildlife protected areas.
Parasite exposure without infection can lead to risk-induced trait responses with potential costs to host fitness or non-consumptive effects (NCEs). The various ways in which NCEs can manifest has gained considerable research attention, but the NCEs of parasite exposure on host mating behaviour remain unknown. Using a host-parasite system involving cactophilic flies (Drosophila nigrospiracula) and ectoparasitic mites (Macrocheles subbadius), we investigated the effects of current and prior parasite exposure (sans infection) on host mating behaviour. Current exposure did not influence host mating behaviour. However, female flies previously exposed to mites exhibited increased copulation latency, and were less likely to mate or be courted by males, suggesting that prior exposure makes females less receptive to mating, or that previously exposed females are less attractive to males. On average, previously exposed males invested less time per mating. Our results demonstrate that prior exposure potentially leads to a trade-off between reproduction and parasite defense even after exposure has ended, likely in favour of increased vigilance and parasite avoidance. While other studies have examined the impact of infection on host behaviour, this study represents the first investigation of NCEs on host mating behaviour. Additionally, our findings suggest that the NCEs of parasite exposure without infection could play an important role in parasite-mediated sexual selection.
Accurately assessing the diversity of myxozoans (Cnidaria) continues to pose a significant taxonomic challenge. Here we evaluated the efficacy of microscopy-based detection in comparison to high-throughput amplicon sequencing by exhaustively screening 942 organ samples from 108 wild fish collected in Lake Weishan, China. Macroscopic and microscopic examination of various fish organs detected only three myxozoan species in 20.4% of the fish, whereas amplicon sequencing achieved 100% detection at the host level and identified 12,672 high-quality amplicon sequence variants (ASVs) that represent at least 102 distinct myxozoan species. Of these, 57 species could be matched to reference sequences, while the remaining 45 lineages constitute putative undescribed species. Species richness varied significantly among hosts (ranging from 24 to 77 species per fish species) and organs (ranging from 2 to 47 species per organ type within each fish species), with gills most frequently exhibiting the highest diversity. Seventy species were found in two or more fish species, and 77 species were detected in multiple organs. Our findings demonstrate that microscopy-based surveys substantially underestimate the diversity of myxozoans and offer the first quantitative framework for future large-scale ecological and pathological investigations of myxozoans.
Schistosomes are parasitic flatworms that infect birds and mammals, including humans, using gastropods as intermediate hosts. Despite their ecological and medical importance, the taxonomy of avian schistosomes is poorly understood due to morphological similarity and patchy molecular data. Here, we present the global synthesis of avian schistosome diversity integrating all available sequence data for three genetic markers (cox1, ITS1-5.8S-ITS2 and 28S rDNA) with newly obtained samples from snails and birds across Europe. Among the markers, cox1 proved to be the most sensitive and reliable for species delimitation and is recommended as the primary barcode for future studies. We identified 25 molecularly confirmed species, representing 29% of the 85 nominal species worldwide, and a further 52 unnamed genetic lineages that may correspond to morphologically known but molecularly unconfirmed species or represent new species. In Europe, we have recognised seven named species and 12 genetic lineages, including six newly discovered lineages based on material obtained from our field collections. To facilitate uniform taxonomy and comparative research, we propose a standardised molecular framework for naming undescribed avian schistosome lineages. Although the morphology of avian schistosome cercariae offers limited taxonomic resolution due to high interspecific similarity, two distinct morphotypes were identified that generally correspond to infections in lymnaeid and planorbid snail hosts.
Tapeworms (class Cestoda) of the genus Hymenolepis are etiological agents of hymenolepiasis, the most prevalent cestode infection in humans, which especially affects children, causing a significant public health impact. Tapeworms have complex life cycles, undergoing morphological and physiological transformations that need precise control of genetic expression. MicroRNAs (miRNAs) are small RNAs that regulate gene expression post transcriptionally, with a prominent role in developmental processes. Previously, we described the microRNA (miRNA) repertoire of Hymenolepis microstoma, a validated laboratory model of the Hymenolepis genus. Here, we aimed to further characterize miRNAs from this parasite, focusing on miR-71, a miRNA previously associated with developmental transitions and potentially involved in cestode infection progression. We identified, for the first time, the predicted miRNA target genes of H. microstoma and H. nana, representing more than 14% of total genes of each parasite. We found that miR-71 was the miRNA with the highest number of predicted target genes, and several of them were related to developmental processes. Here we also characterized, for the first time, the spatial expression of miRNAs in whole H. microstoma specimens. The analysis showed that miR-71 displayed broad expression across tissues, including germinative, nervous, and muscular systems, supporting a central regulatory role. Notably, it was also detected in germinative cells, the only mitotically active population responsible for generating all differentiated cell types. In contrast, the highly conserved miR-1 had a highly restricted expression pattern, predominantly localized in myocytes. This study improves characterization of tapeworm miRNAs and paves the way for future experimental research in cestode biology, providing, as well, a source for identification of novel biomarkers and therapeutic targets for the control of cestodiasis.
Amblyomma testudinarium sensu lato, a vector of medically important pathogens, including severe fever with thrombocytopenia syndrome virus, represents a species complex known from East Asia, South Asia, and Southeast Asia. Genetic and distributional data pertaining to these ticks are scattered, challenging One Health strategies. Using genetic information and distributional records of A. testudinarium s.l. and related species, we found two clades of A. testudinarium. We also found that Amblyomma javanense and Amblyomma varanense likely represent species complexes. We project the geographic ranges of the two A. testudinarium clades, highlighting variation in disease risk and gaps in knowledge that need to be answered for the betterment of public health.
Hookworms infect nearly half a billion people, causing approximately 2.1 million disability-adjusted life-years lost. While anthelmintic drugs are available, they do not prevent reinfection. A vaccine could provide long-term immunity, but none currently exists. We recently demonstrated that human subjects could be safely vaccinated with irradiated hookworm larvae, eliciting humoral and cellular immune responses that induce partial protection against challenge infection with non-irradiated parasites. Using immunomic approaches, we identified IgG targets in vaccinated individuals by screening a proteome microarray containing recombinant proteins sourced from the secretome of Necator americanus. We characterized the most immunoreactive N. americanus proteins and identified their orthologs in the rodent hookworm Nippostrongylus brasiliensis. These N. brasiliensis proteins were expressed recombinantly and tested for efficacy in a mouse challenge model. Our lead vaccine candidate NBR17057 - a homolog of Na_11335 provided robust protection against infection, evidenced by >90% reductions in intestinal worm burden and fecal egg counts, and elevated antigen-specific IgG levels. Vaccination also stimulated IgA+ B-cells, IgG1+/IgA+ plasma cells, and IgG1+/IgA+ germinal centre B-cells in inguinal lymph nodes, indicating gut immunity. Additionally, high levels of IgG1+/IgA+ B-cells, germinal centre B-cells, and plasma cells in the spleen suggest protection against systemic larval migration. The presence of IgG1+/IgA+ memory B-cells in both the lymph nodes and spleen indicates potential long-term immunity against reinfection. Our findings suggest that a N. brasiliensis L3 larval-stage protein NBR17057 and its homolog in N. americanus Na_11335 could serve as a promising subunit vaccine candidate targeting the infective larval stage of human hookworms.
Heterogeneity of internal parasite communities amongst host animals is shaped by processes at multiple scales, including landscape distribution of parasites, individual host suitability, and parasite interactions within a host. As a result, pathogen co-occurrence patterns vary across space and time and among host populations. Often the challenges of wildlife sampling limit understanding of the drivers of pathogen community heterogeneity in host animals. In this study, we explore patterns and drivers of parasite community heterogeneity amongst wild bighorn sheep (Ovis canadensis) hosts over time and across populations. We describe temporal patterns including (i) general seasonal patterns of nematode and coccidia infection and (ii) taxon-specific patterns that differ by parasite life histories for bighorn sheep in southeastern Oregon and northern Nevada over a five-month period. Additionally, we describe patterns of parasite associations, many of which appear to result from co-occurrence on the landscape and others that may arise from interactions among parasites within a host. At a lower taxonomic resolution, coccidia and nematodes were positively associated with Normalized Difference Vegetation Index (NDVI), a measure of landscape vegetation greenness; at a higher taxonomic resolution, Protostrongylus was the only nematode positively associated with NDVI. Eimeria was positively associated with Ostertagia and negatively associated with Marshallagia, both abomasal nematodes. These two associations were independent of host geographical distribution and landscape vegetation greenness, suggesting that these co-occurrences may be a result of parasite interactions. This study establishes a recent and geographically expansive exploration of internal nematodes and coccidia present in a wildlife system comprising multiple populations and demonstrate the need for future investigation into parasite interactions.
The golden jackal Canis aureus is regarded as a potential bridge host for emerging parasites in Europe to domestic animals, owing to its adaptability to live in human-dominated landscapes. As the species continues to expand in Europe, copromicroscopy offers a non-invasive alternative to necropsy-based methods to obtain epidemiology data, but its performance on jackals has never been assessed. We compared the performance of two copromicroscopic tests, flotation technique (FT) and Mini-FLOTAC (MF), to the Scraping, Filtration and Counting technique (SFCT), current standard for helminth detection, and assessed their agreement. The intestinal contents and corresponding fecal samples from 84 golden jackals were examined. Sensitivity and specificity of FT and MF relative to SFCT were estimated for each detected taxon (Toxocara canis, Trichuris vulpis, strongylids, Mesocestoides spp., and Taenia spp.). Associations between adult parasite burden and copromicroscopic positivity were explored using non-parametric tests and logistic regression models. Agreement between FT and MF was assessed using concordance and Gwet's γ(AC1). Both FT and MF detected the most prevalent helminth species at SFCT, but showed low sensitivity, ranging from 28.6% to 56.5%. Parasite intensity did not significantly influence copromicroscopic positivity for most taxa, and quantitative MF results did not linearly reflect parasite loads. The two methods showed comparable performance, suggesting that their use may be guided by operational constraints and study objectives. Despite their limitations, copromicroscopic techniques represent useful tools for epidemiological surveillance in jackal populations, provided that adequate sample sizes are used and prevalence estimates are adjusted for test sensitivity and specificity.
