The Barbary partridge (Alectoris barbara), an endemic game bird in Algeria, has not been systematically investigated for parasitic infections despite its ecological, economic, and conservation importance. This study provides the first eco-epidemiological and histopathological assessment of Capillaria contorta infection in birds from a semi-captive breeding center in Zeralda, Algeria. Between 2021 and 2024, 1085 pooled fecal samples and 138 postmortem examinations were analyzed using standard parasitological and histopathological methods. C. contorta showed an aviary-level overall prevalence of 32.94% and was involved in 42.02% of parasite-related mortalities, underscoring its marked pathological significance. Aviary-level prevalence varied significantly across seasons and years (p < 0.05), with higher levels recorded during environmentally favorable periods. Mixed infections with helminths, protozoa, cestodes, and ectoparasites were recorded for the first time in this host species at the aviary level, highlighting complex parasite interactions. Morphological characteristics were consistent with C. contorta. Gross examination revealed marked thickening of the esophagus and crop. Histologically, the adult nematodes were embedded within hyperplastic epithelium, with characteristic bipolar-plugged eggs and associated epithelial tunnels, accompanied by chronic inflammation and granulomatous reactions. These findings demonstrate the clinical relevance of C. contorta and emphasize the need for strengthened surveillance and control programs to reduce infection pressure and prevent potential spillover to wild populations.

A new species of Prodistomum (Digenea, Lepocreadiidae), Prodistomum chumphonense sp. nov., is described from the intestine of Rastrelliger kanagurta and Rastrelliger brachysoma (Scombridae) collected in the Gulf of Thailand. The new species is characterized by vitelline follicles confined to the hindbody but extending anteriorly to the level of the anterior to posterior margin of the ventral sucker; a ventral sucker consistently larger than the oral sucker; an esophageal region approximately equal in length to the prepharynx; an entire, oval ovary; and a tubular excretory vesicle terminating below the level of the intestinal bifurcation. The new species differs from most congeners, mainly those with vitelline follicles extending into the forebody, by the restriction of the vitellarium to the hindbody. Although morphometrically similar to some specimens in the literature previously identified as P. orientale, previous molecular phylogenetic analyses based on 18S, ITS2, and 28S rDNA sequences demonstrate that P. chumphonense sp. nov. represents a distinct taxon. The present study underscores the importance of integrating detailed morphometric with molecular data for accurate species delimitation in trematodes of the genus Prodistomum.

Infectious agents shape fish populations by inducing lethal and sublethal changes that alter nutrient metabolism and metal bioaccumulation. These shifts can manifest as changes in the ionome—the specific combination of essential and non-essential chemical elements defining the whole-body composition of an individual. Understanding how pathogens shape the fish ionome is critical for developing advanced monitoring tools and clarifying the ecological roles of hosts and their pathogens. This study reports the first documented outbreak of Citrobacter freundii, Pseudomonas aeruginosa, Pseudomonas mosselii, and Shewanella xiamenensis bacterial infections in wild-caught eastern mosquitofish (Gambusia holbrooki) from three populations in Extremadura, southwestern Spain. Under laboratory-controlled conditions, we established associations between these bacterial outbreaks and the whole-fish body ionome of G. holbrooki. We compared 19 chemical elements and seven elemental ratios among diseased fish, healthy fish at the outbreak, and individuals fully recovered 100 days post-infection following antibiotic treatment. The fish ionome clearly discriminated between diseased and healthy states, and the response was consistent across all three populations. Our findings support the utility of whole-fish body elemental composition in G. holbrooki as a biomarker for environmental monitoring. Furthermore, as the bacterial infections were associated with the capture and transport-induced stress of wild individuals, this study provides critical data on the opportunistic pathogens that may be co-introduced into recipient ecosystems through the release of this widely distributed invasive fish species.

IntroductionThis study investigates the helminth absence in the invasive blackchin tilapia (Sarotherodon melanotheron) in Thailand, testing the Enemy Release Hypothesis (ERH). The ERH suggests that invasive species thrive in new habitats due to the lack of natural parasites that control their populations in native environments. The recent introduction of S. melanotheron in Thailand has raised concerns about its ecological and economic impacts.MethodsWe surveyed 164 blackchin tilapia from six different locations in Chumphon Province, Thailand, including the sea, estuary, canal, and shrimp farms, examining them for helminths. Fishermen provided data on the first capture dates in the surveyed areas to determine how long the populations have been established.ResultsNo helminths were detected in any of the examined fish. The absence of parasites was consistent across all surveyed environments, suggesting a lack of parasitic burden in the population.DiscussionThe absence of helminths may contribute to the successful expansion of S. melanotheron in Thailand, supporting the Enemy Release Hypothesis.

Co-infections between helminths and microparasites can modulate the host immune response and alter disease dynamics, with potential implications for public health. However, identifying causal relationships in natural populations is challenging due to the complexity of ecological interactions. Perturbation experiments, where a specific parasite is selectively reduced, offers a powerful framework to directly test such interactions under natural conditions. In this study, we investigated potential helminth-microparasite interactions in the multimammate mouse (Mastomys natalensis) in Tanzania by experimentally reducing helminth infections in both captive and wild populations. We first confirmed that two anthelmintic treatments, ivermectin and pyrantel pamoate, effectively reduced gastrointestinal nematode burdens in wild-caught individuals. We then assessed whether helminth reduction influenced the prevalence of viral and bacterial infections in free-living populations. Our results revealed no significant short-term effect of anthelmintic treatment on microparasitic infections. These findings suggest that helminth-microparasite interactions in M. natalensis may be subtle, context-dependent, or require longer timescales to become apparent.

The present study describes the morphology and phylogenetic position of two specimens of Bertiella Stiles et Hassall, 1902 (Cestoda, Anoplocephalidae) from Rattus tanezumi (Temminck) (Muridae) from Đồng Tháp Province in southern Vietnam. The phylogenetic analysis was based on sequences of the large subunit ribosomal RNA gene (28S). The specimens were described and shown to be morphologically similar to Bertiella anapolytica Baylis, 1934 from Rattus spp. from Indonesia (Sumatra, type locality) and Australia, except for a few quantitative differences. The identification was confirmed by the phylogenetic analysis, which showed a strong affinity and fairly limited genetic divergence between the specimens from Vietnam and Australia. This is the first verified case of Bertiella in murid rodents from continental Eurasia. The uterine pore and associated canal present in the posterolateral corners of gravid proglottids of B. anapolytica are considered to form a true, functional structure used for egg release prior to apolysis. The phylogenetic analysis suggested that B. anapolytica has diverged as a consequence of a shift from marsupials, which probably took place east of the Wallace's line, either in Wallacea or Australasia. The presence of B. anapolytica west of the Wallace's line (Vietnam, Sumatra), where marsupials are absent, may be explained by a westward dispersal in commensal rats, possibly Rattus exulans (Peale), a species transported throughout the Pacific and South-East Asia by prehistoric people.

During an ichthyoparasitological survey in northeast Thailand in 2015, four species of acanthocephalans were found in four species of freshwater fishes. Adult stages of Pallisentisrexus Wongkham & Whitfield, 1999 and Raosentis sp. (Eoacanthocephala, Quadrigyridae) were collected from Channastriata (Anabantiformes, Channidae) and Mystusmysticetus (Siluriformes, Bagridae), respectively, and cystacanths of Arhythmorhynchus sp. (Palaeacanthocephala, Polymorphidae) were found on the visceral organs of M.albolineatus (Siluriformes, Bagridae). Adult acanthocephalans of the subgenus Acanthosentis Verma & Dutta, 1929 isolated from Barbonymusschwanenfeldii (Cypriniformes, Cyprinidae) were morphologically distinct from all described species of the subgenus in the arrangement of rings of tegumental spines in two fields with a more or less pronounced distance between them, and by the presence of a dome-shaped process with a ring of small spines at the base at the posterior end in females. Molecular data were generated for three species and phylogenetic analysis based on the 18S rDNA clearly supported the generic identification of Acanthogyrus (Acanthosentis) barbonymisp. nov. and P.rexus. While the phylogenetic position of the former species within the genus could not be clarified, the latter species formed a well-supported sister lineage in a clade with isolates of four congeneric species. Acanthogyrus (Acanthosentis) barbonymisp. nov. is formally described, the first genetic data for P.rexus are generated, a species of the genus Raosentis Datta, 1947 is reported for the first time outside the Indian subcontinent, and a key to the species of the latter genus is presented.

Parasites are expected to hybridise in similar ways to free-living organisms, although this may be modified by their reduced genome architecture. Recombinant strains and taxa of hybrid origin can be studied in nature where hosts come into secondary contact. Here we apply genome-wide analysis to parasites from a contact previously characterised for many individuals using classical markers. The host contact is the European house mouse hybrid zone; the parasites are lung fungus Pneumocystis and gut pinworm Syphacia. The genomic (many loci) and classical (many-individual) results are broadly consistent in scale and centring of transitions across the host hybrid zone. Whole mitogenome comparisons confirm earlier suggestions that parasite divergence is low compared to their hosts, perhaps due to reduced-genome stabilising selection. In the recombining genome, we are able to show blocks of the parasite genome of alternating host origin, including one Pneumocystis strain which appears to be an F3+ cross and one recombinant Syphacia strain found over multiple localities. Functional analyses of introgressing genes show enrichment for genes likely important for parasitic lifestyle. Our work confirms that evolutionary models of hybridisation apply equally to hosts and their parasites.

Background Studies of insect biodiversity and parasitism are often based on adult stages, as immature stages are poorly known and often cannot be identified to species level. However, sucking lice (Anoplura) are permanent, hematophagous parasites with single-host life cycles, making it possible to track the occurrence of all life stages. Only the complete identification of all life stages provides a full picture of parasitism, including infestation levels, parasite topography preferences on the host, and host specificity. The detection of different development stages on a host provides strong evidence that lice of a particular species are actively reproducing and completing their life cycle on that host, making full use of its resources. Conversely, the presence of adult lice alone, particularly when found sporadically, may suggest a failed or incidental attempt at host colonization rather than an established parasitic association. Methodology The description of the nymphal stages of Hoplopleura malabarica is based on specimens of sucking lice from the greater bandicoot rat Bandicota indica from Southeast Asia, specifically from the Vientiane area of Lao PDR. The study used morphometric analysis and scanning microscopy techniques. Results This study presents the first description of the nymphal stages of Hoplopleura malabarica, an oligoxenous parasite of rodents of the genus Bandicota. In addition, a global checklist of Anoplura parasitizing rodents of the genus Bandicota was provided. Conclusions The detection of different life stages of lice within the host confirms that they reproduce and develop on a given host species, fully utilizing its resources.

The Gulf of Thailand is a highly diverse marine ecosystem, yet knowledge of its helminth fauna remains fragmentary. Marine fishes were obtained in 2024 from accidental catches of crab-trap fishers or captured by local fishermen using boats in Chumphon Province, Thailand. In this study, we molecularly characterize three digenean trematode genera parasitizing marine fishes from this area: Lecithocladium (Hemiuridae) from the short mackerel (Rastrelliger brachysoma), with a prevalence of 77% in 22 fishes and ten worms examined for morphology; Prodistomum (Lepocreadiidae) from R.brachysoma, with a prevalence of 18% in 22 fishes, and from Rastrelliger kanagurta, with a prevalence of 100% in one fish, with 10 worms examined for morphology; and Lepocreadioides (Lepocreadiidae) from the double-lined tonguesole (Paraplagusia bilineata), with a prevalence of 75% in four fishes, and eight worms examined for morphology. Sequences of nuclear ribosomal markers (18S, ITS2, and 28S) were generated, providing the first molecular data for Lepocreadioides orientalis. Our analyses confirm the presence of Lecithocladium angustiovum and Prodistomum sp. in the Gulf of Thailand, contribute new molecular data, and provide a morphological description of Prodistomum sp. Despite the Gulf of Thailand’s high ichthyofaunal diversity, its helminth communities remain insufficiently investigated, highlighting the need for future research.

The nematode Spinitectus inermis (Zeder, 1800), a specific gastrointestinal parasite of Anguilla anguilla, has been recorded for the first time in the Italian Peninsula. The study was conducted in the Mesima River, located in the southwestern part of the Calabria region (southern Italy). Over a five-month period, 162 specimens of European eel were sampled, revealing an overall prevalence of 47.53%, a mean intensity of 9.51 (±13.88), and a mean abundance of 4.55 (±10.69). The nematode was present throughout the five months analyzed, with prevalence rates ranging from 32.0% to 57.14%. The overall prevalence in the Mesima River was higher than in most previous studies, and the mean abundance of infection was also higher. The highest prevalence of infection was observed in September (56.7%), October (57.14%), November (48.57%), and December (40.54%), with the lowest in March (32.0%). In conclusion, Spinitectus inermis appears to be well established in the eel population of the Mesima River, exhibiting high prevalence and intensity year-round despite ecological variations, though its intermediate hosts remain unknown.

The classification of the digenean genus Gogatea Lutz, 1935 has been complicated for almost a century due to morphological variability and reliance on limited diagnostic traits. This study re-evaluates the taxonomic status of Gogatea serpentum (Gogate, 1932) and Gogatea burmanicus (Chatterji, 1940) using an integrative framework combining morphology and molecular phylogenetics. Trematodes were recovered from the gallbladder and intestine of the rainbow water snake (Enhydris enhydris) in southern Thailand. Morphological investigations included morphometrics, acetocarmine-stained preparations, scanning electron microscopy and multivariate analyses, while molecular analyses used mitochondrial COI and nuclear ITS2 and 28S rRNA markers. Both gonad-bearing and gonad-less individuals exhibited identical sequences across all markers, forming a strongly supported monophyletic group. Morphological variation was restricted to the presence or absence of gonads, with no separation detected by principal component analysis. These findings support the synonymization of G. burmanicus as a junior synonym of G. serpentum (following the original spelling by Gogate, 1932, as validated under the ICZN [International Code of Zoological Nomenclature]). The occurrence of gonad-less adults represents a biologically intriguing phenomenon, the causes of which remain unresolved but may involve developmental, host-related, or ecological factors. This study underscores the importance of combining molecular and morphological approaches for accurate delimitation of morphologically plastic digeneans. Updated morphological descriptions and molecular data for G. serpentum are provided, including morphometrics, staining profiles, scanning electron microscopy micrographs and genetic sequences. These findings refine the taxonomy of Gogatea, advance knowledge of helminth diversity in semi-aquatic snakes and support broader efforts in parasite systematics, host-parasite ecology and biodiversity monitoring in Southeast Asia.

Emerging infectious diseases are one of the main threats to global amphibian populations. Frogs and salamanders are already affected by various pathogens, including ranaviruses, Batrachochytrium dendrobatidis, B. salamandrivorans, and helminths. Here, we report the first confirmed cases of Ichthyophthirius multifiliis, a ciliate parasite traditionally considered fish-specific, infecting wild amphibian larvae in a natural setting. As part of a passive surveillance program in Catalonia, five dead amphibians (four S. salamandra larvae and one Rana temporaria post-metamorph) were collected from a freshwater spring and examined for common pathogens. All individuals tested negative for chytrid fungi and ranaviruses by qPCR. However, histological examination of gill tissue revealed the presence of I. multifiliis trophonts in three of the salamander metamorphs and in the frog post-metamorph. In addition, larvae of forty-two amphibians from other localities in Catalonia tested negative. The observed trophonts matched morphological features previously described in teleost infections, including their characteristic macronucleus and surface ciliation. Our results further validate the previous molecular detections and experimental evidence suggesting the parasite’s potential for cross-taxon infection, raising concerns about the overlooked potential prevalence of I. multifiliis in wild amphibians. Given the increasing impact of climate change and habitat alteration on global freshwater ecosystems, this study highlights the importance of including I. multifiliis in amphibian disease monitoring programs.

Heterakis spumosa, a parasitic worm infecting rodents, is globally prevalent in black rats, brown rats, and house mice. It is hypothesized to originate from Asia due to its widespread presence in Southeast Asia in various Murinae. Previous molecular studies focused on European, African, and Japanese specimens, but none included samples from the putative native range. Rodents were collected between 2008 and 2015 across various localities in Southeast Asia and Europe, identified by morphology or genetic barcoding. Viscera were examined or preserved for later inspection. DNA was extracted from H. spumosa. PCR amplification targeting the mtCOI gene and ITS1 region was conducted in this study using newly designed primers (based on Heterakis reference sequences). PCR amplicons were subsequently sequenced and analyzed. In this study, the phylogenetic analysis using ITS1 sequences revealed that Heterakis samples from Thai and Laotian rodents belong to the species H. spumosa, exhibiting low genetic variation compared to samples from other regions. Genetic distance calculations using mtCOI sequences confirmed the marked distinction of H. spumosa from other Heterakis species. Our phylogenetic analyses using partial mtCOI and ITS1 sequences have significantly enhanced our comprehension of the genetic diversity and evolutionary history of the nematode H. spumosa.

The present study aims at clarifying the poorly known phylogenetic relationships and systematics of cestodes of the family Davaineidae Braun, 1900 (Cyclophyllidea), primarily the genus Raillietina Fuhrmann, 1920 and of the subfamily Inermicapsiferinae (Anoplocephalidae) from mammals (mostly rodents, 31 new isolates) and birds (eight new isolates). Phylogenetic analyses are based on sequences of the large subunit ribosomal RNA gene (28S) and mitochondrial NADH dehydrogenase subunit 1 gene ( nad1 ). The main phylogenetic pattern emerging from the present analysis is the presence of three independent lineages within the main clade of the subfamily Davaineinae, one of which is almost entirely confined to species from rodents and the other two show a mixture of species from birds and mammals. It is suggested that the major diversification of the main clade took place in birds, possibly in galliforms. The subsequent diversification included repeated host shifts from birds to mammals and to other birds, and from rodents to other mammals, showing that colonisation of new host lineages has been the main driver in the diversification of davaineine cestodes. It is also shown that all isolates of Inermicapsifer Janicki, 1910, mainly from rodents, form a monophyletic group positioned among Raillietina spp. in the "rodent lineage", indicating that the genus Inermicapsifer is a member of the family Davaineidae. This means that the subfamily Inermicapsiferinae and the family Inermicapsiferidae should be treated as synonyms of the Davaineidae, specifically the subfamily Davaineinae. Three additional genera generally included in the Inermicapsiferinae, i.e. Metacapsifer Spasskii, 1951, Pericapsifer Spasskii, 1951 and Thysanotaenia Beddard, 1911, are also assigned here to the Davaineidae (subfamily Davaineinae). Raillietina spp. were present in all three main lineages and appeared as multiple independent sublineages from bird and mammalian hosts, verifying the non-monophyly of the genus Raillietina and suggesting a presence of multiple new species and genera.

The formalin-ethyl acetate concentration technique (FECT) is one of the most sensitive diagnostic method not only for all helminths, but also for Opisthorchis viverrini infections in stool examinations. However, it remains a diagnostic problem for light infections. We modified the one-step FECT to determine the low-intensity of O. viverrini infection and compared with various conventional detection methods. The study utilized 160 egg-positive and 160 randomly negative stool samples for O. viverrini eggs by conventional FECT (cFECT) to compare the methods, including the simple smear, the Kato-Katz method, the two commercial stool examination kits, and the one-step FECT. Our results showed that the one-step FECT method had the highest sensitivity (95.6 %), followed by cFECT (87.9 %), the Kato-Katz (55.5 %), Aquisfek SF-FIX (R) (48.3 %), simple smear (42.3 %), and Mini Parasep (R) SF (35.1 %). The ability of one-step FECT exhibited better ability to detect low parasite intensities compared to the cFECT (18 eggs per gram (e.p.g.) versus 34 e.p.g.) and the other conventional diagnostic methods. In addition, the investigation of O. viverrini infection in endemic regions in northeastern Thailand based on 3900 fecal samples revealed that the one-step FECT with an intensity of 66.8 e.p.g. (range 18-226) was significantly higher in sensitivity than cFECT, which had an intensity of 58.0 e.p.g. (range 34-214). Interestingly, fecal samples with less than 50 e.p.g. could not be detected by cFECT in 67 % of cases, and 69 out of 3900 samples were negative. In conclusion, one-step FECT improves the detection of low-intensity O. viverrini infection, which is suitable for parasites screening, especially for low-intensity infections in the community.

The study of sperm characteristics has proven useful for elucidating interrelationships in several groups of Platyhelminthes, such as digeneans. Thus, in the present work, the ultrastructural organization of the mature spermatozoon of the digenean Artyfechinostomum malayanum (Echinostomatidae), a parasite of Rattus norvegicus (Rodentia: Muridae) from Dong Thap Province, Vietnam, was investigated for the first time using transmission electron microscopy. The male gamete of A. malayanum exhibits two axonemes of different lengths, showing the 9 + ‘1’ pattern of the Trepaxonemata, a nucleus, two mitochondria, two lateral expansions, two bundles of parallel cortical microtubules, external ornamentation, spine-like bodies, and granules of glycogen. Thus, the mature spermatozoon follows a Type V sperm model proposed for digeneans. We also highlight some noteworthy characteristics in Echinostomatidae with possible phylogenetic implications, such as two lateral expansions in the anterior region of the spermatozoon and two mitochondria.

The ultrastructural features of the mature spermatozoon of Telorchis attenuatus (Digenea, Telorchiidae), an intestinal parasite of the red-eared turtle Trachemys scripta elegans (Testudines, Emydidae), are described using transmission electron microscopy (TEM). The mature spermatozoon of T. attenuatus is a filiform cell tapered at both ends and displays Bakhoum et al.’s type IV of digenean sperm cells. Spermatozoa of T. attenuatus have: (i) two axonemes of different lengths with the 9+'1' pattern of trepaxonematan Platyhelminthes, surrounded by a continuous submembranous layer of cortical microtubules at their anterior end, (ii) an external ornamentation of the plasma membrane following Quilichini et al.'s type 2 and associated with cortical microtubules, (iii) two bundles of parallel cortical microtubules with the maximum number situated in the anterior part of the sperm cell, (iv) spine-like bodies, (v) two mitochondria, and (vi) a large number of irregularly distributed glycogen granules. Furthermore, the morphology of the posterior spermatozoon extremity in T. attenuatus corresponds to the Quilichini et al.'s fasciolidean type. The results of the current study are especially compared to the existing information from other families within the superfamily Plagiorchioidea.

Nematodes belonging to the genus Oesophagostomum frequently infect wild chimpanzees (Pan troglodytes) across widely separated field sites. Nodular lesions (granulomas) containing Oesophagostomum are commonly seen in the abdomen of infected chimpanzees post-mortem. At Taï National Park, Côte d'Ivoire, previous studies have identified larvae of a variety of Oesophagostomum spp. in wild chimpanzee stool, based on sequencing of larval DNA, and nodular lesions associated with Oesophagostomum, identified morphologically to the genus level but not sequenced. Here we present three recent cases of parasitic granulomas found post-mortem in chimpanzees at Taï. We complement descriptions of gross pathology, histopathology and parasitology with PCR and sequencing of DNA isolated from the parasitic nodules and from adult worms found inside the nodules. In all three cases, we identify Oesophagostomum stephanostomum as the causative agent. The sequences from this study were identical to the only other published sequences from nodules in nonhuman primates-those from the wild chimpanzees of Gombe, Tanzania.

Host–parasite interactions are influenced by present and past eco‐evolutionary interactions and the local environment. An ecological community defines the potential host range of each parasite and the potential parasite diversity of each host species. Past and present processes translate potential to realised interaction niches of parasite and host species. Host–parasite interactions are antagonistic, which may slow the saturation of their interaction niches. Intervality, a property of bipartite networks, measures saturation of interaction niches. Intervality of a community increases as the interaction niches of species of one guild (e.g. hosts) become saturated for their interactions with another guild (e.g. parasites). Characteristics driving intervality in host and parasite communities are largely unknown, as well as the effect of environmental change on intervality of these communities. In our study, we assess if the characteristics ‘phylogenetic relatedness' and ‘overlap in ecological interactions' explain intervality of rodent host–helminth parasite communities. In addition, we contrast intervality of these communities from habitats that differ in their history of human‐driven modification. We performed the analyses for the interaction niches of both parasites and hosts, independently. Our results indicated that host and parasite communities were non‐interval or significantly less interval than expected by chance. Phylogenetic relatedness and overlap in ecological interactions did not explain the maximum values of intervality. We speculate that antagonistic coevolution in host–parasite communities may hinder communities to reach saturation, which would explain why it is difficult to find the characteristics that explain intervality of a community. Interestingly, intervality of the interaction niche of parasites (host range) increased with habitat modification (i.e. saturation increased), whereas intervality of the interaction niche of hosts (parasite diversity) decreased as habitat modification increased. These opposite trends suggest that interaction niches of parasites and hosts respond differently to habitat modification.