Distinguishing between Stomylotrema bijugum and S. vicarium is challenging due to their phenotypic plasticity. In this study, adult specimens were recovered from 9 host species in the Mexican tropical lowlands. To explore the morphological differences, 32 morphological characteristics were evaluated in 54 specimens. Linear discriminant analysis provided enough evidence to differentiate the 2 species. Additionally, a principal component analysis (PCA) was performed for each species. The PCA of S. bijugum revealed 3 groups separately corresponding to specimens from the 3 hosts, suggesting host-induced phenotypic plasticity, whereas the PCA of S. vicarium revealed that the specimens from 3 host species were clustered together, indicating morphometric homogeneity. To confirm the morphological differences between the 2 species of Stomylotrema, we sequenced 2 molecular markers: the D1–D3 domains of the large subunit (LSU) from nuclear DNA and nicotinamide adenine dinucleotide dehydrogenase subunit 1 (Nad1) from mitochondrial DNA. Sequences of the LSU were aligned and compared with the LSU sequences of other congeneric species available in GenBank. Phylogenetic analyses supported the monophyly of Stomylotrema, with 2 main subclades that corresponded to S. bijugum and S. vicarium. A haplotype network was predicted with 25 Nad1 sequences, revealing the presence of 2 clusters representing the 2 species separated from each other by 98 substitutions. The current studies on S. bijugum and S. vicarium revealed new hosts and geographical regions in the Americas, suggesting that both species addressed in the current study can complete their life cycle in the Neotropical region of Mexico.

Population dynamics of aquatic parasites respond to factors like host availability, habitat age and quality. Amphipods are intermediate hosts for Acanthocephala, a widespread group of parasitic worms. Acanthocephalan infections of amphipods can easily be detected, and the widespread occurrence of amphipods makes their infection status an attractive potential proxy for the ecological status of their aquatic environment, including stressors introduced by urbanization. This study investigated the prevalence and the species-level and genetic diversity of Acanthocephala in the stream amphipod Gammarus fossarum. The study streams cross forested, agricultural and urban landscapes in the eastern foothills of the European Alps. Parasite prevalence ranged from 0% to 8.8% and increased towards downstream reaches independent of surrounding land use. Oxford Nanopore Technology was used to sequence the mitochondrial cytochrome oxidase I barcoding locus to identify parasite species and assess their genetic diversity. The majority of the parasites were Pomphorhynchus tereticollis, which use fish as definitive hosts. Despite their relative abundance in the studied streams, their genetic diversity was low and the most common haplotype was found at all sampling sites, which might indicate population expansion. Amphipods also hosted P. laevis and Polymorphus sp. type 1, the first evidence of this cryptic species within Polymorphus cf. minutus in Austria. Genetic diversity was high in Polymorphus sp. type 1, possibly reflecting a large effective population size due to gene flow maintained by the avian final hosts. The low and downstream-biased prevalence suggests that definitive hosts may be a limiting factor for Acanthocephala populations in small streams.

Echinococcosis, caused by cestodes of the genus Echinococcus, poses significant public health and veterinary concerns globally. In Armenia, cystic echinococcosis (CE) is well-documented in livestock and humans, while alveolar echinococcosis (AE) has long been considered non-endemic. However, a recent retrospective study identified human AE cases, suggesting an underestimation of the parasite’s presence. To address knowledge gaps, a pilot survey was conducted to identify Echinococcus species and other taeniids in free-roaming dogs and wild carnivores in Armenia. Fecal samples (n = 112) were opportunistically collected from eight wild carnivore species and stray dogs across six Armenian provinces between 2017 and 2018. Samples were analysed for taeniid eggs using flotation and molecular techniques. Echinococcus multilocularis was identified in a free-roaming dog, marking the first confirmed detection of the parasite in a definitive host in Armenia. Additionally, E. canadensis G6/7 and E. ortleppi were detected in a wolf, while E. canadensis G6/7, Taenia hydatigena, and T. laticollis were found in a lynx. These findings indicate the involvement of both domestic and wild carnivores in the transmission cycles of Echinococcus species and suggest the presents of a potential sylvatic cycle involving E. canadensis G6/7 and E. ortleppi. The presence of E. multilocularis in a dog underscores the risk of human infection, necessitating further epidemiological studies. This study provides initial insights into the epidemiology of Echinococcus in Armenia and highlights the need for continued surveillance to assess public health risks.

Ochoterenella is a large group of filarial parasites of anurans distributed throughout Central and South America. In the present study, we describe a new species of Ochoterenella parasitizing 2 frogs, Boana geographica and Boana multifasciata, from different localities in the Brazilian Amazon. The main morphological traits that differ Ochoterenella casiraghii n. sp. from its congeners are the smaller body size, a shorter cephalic plate, smaller parastomal structures, and the small, short and rounded cuticular bosses on the body of both sexes. The females have a shorter ovejector, and the number of caudal papillae distinguishes males. Pairwise sequence comparisons of the new species reveal a high level of divergence from Ochoterenella spp. Our phylogenetic analyses, based on cox1 and concatenated partial mitochondrial genes, support the monophyly of all subfamilies and genera examined herein. The new species represents the 17th in the Ochoterenella genus and a new parasite record for both anuran species. We provide the first ultrastructural description of the species in the genus and establish the phylogenetic relationships of the new species among parasites of amphibians and reptiles from the Onchocercidae.

The migratory phase is a critical time for Fasciola hepatica as it must locate, penetrate and migrate through the alimentary tract to the liver parenchyma whilst under attack from the host immune response. Here, scanning and transmission electron microscopy were used to monitor the in vitro effects of sera (with, and without, complement depletion) on F. hepatica newly excysted juveniles (NEJs) and flukes recovered at 7, 35, 70 and 98 days post infection (dpi) from the liver and bile ducts of rats. Test sera were from these F. hepatica-infected rats. A F. hepatica NEJ-specific rabbit antiserum was also used. All fluke stages demonstrated release of the tegumental glycocalyx and microvesicles and intense activity within the tegumental syncytium characterized by eccrine secretion of T-0/T-1/T-2 secretory bodies with subsequent microvillar formation and shedding of microvesicles from the apical plasma membrane. Exposure of both NEJs and 35 dpi flukes to 35 and 70 dpi rat sera produced significant amounts of eccrine-derived secretory material and putative attached immunocomplex. Rabbit anti-F. hepatica NEJ-specific antiserum produced similar responses at the NEJ tegument, including binding of putative immunocomplex to the surface, but with additional blistering of some regions of the apical plasma membrane. Our data suggest that immune sera stimulates multiple interrelated secretory mechanisms to maintain the integrity of the tegumental barrier in response to immune attack. Concurrent release of microvesicles may also serve to both divert the immune response away from the fluke itself and permit delivery of immunomodulatory cargo to immune effector cells.

Detection approaches based on environmental DNA (eDNA) are widely used for free-living species but remain underutilized for parasite species. This study applies eDNA detection methods to elucidate the life cycle of the trematode Curtuteria arguinae, which infects the socioeconomically and ecologically important edible cockle (Cerastoderma edule) as its second intermediate host along the northeastern Atlantic coast, including Arcachon Bay, France. The first intermediate and definitive hosts remained unknown. To identify these hosts – presumed to be a gastropod and a shorebird – we developed a quantitative PCR (qPCR)-based eDNA approach targeting partial cox1 and SSU gene regions of C. arguinae. We tested for C. arguinae eDNA presence in water samples containing separately five dominant gastropod species and fecal samples from known cockle predators, the European oystercatcher (Haematopus ostralegus) and gulls (Larus spp.), collected in Arcachon Bay. C. arguinae eDNA was only detected in water containing the needle snail (Bittium reticulatum), with cercarial emergence confirming infection in 1.6% of individual hosts. Morphological analysis of the cercarial and metacercarial stages revealed variability in collar spine visibility. Additionally, C. arguinae was detected by qPCR in 42% of oystercatcher feces and no gull feces, suggesting oystercatchers are the definitive host. This study is the first to elucidate the complete life cycle of C. arguinae, identifying B. reticulatum as its first intermediate host and H. ostralegus as its definitive host. Our findings highlight the potential of eDNA approaches for resolving parasite life cycles and enabling advances in ecological research on C. arguinae.

High density should drive greater parasite exposure. However, evidence linking density with infection generally uses density proxies or measures of population size, rather than measures of individuals per space within a continuous population. We used a long-term study of wild sheep to link within-population spatiotemporal variation in host density with individual parasite counts. Although four parasites exhibited strong positive relationships with local density, these relationships were mostly restricted to juveniles and faded in adults. Furthermore, one ectoparasite showed strong negative relationships across all age classes. In contrast, population size – a measure of global density – had limited explanatory power, and its effects did not remove those of spatial density, but were distinct. These results indicate that local and global density can exhibit diverse and contrasting effects on infection within populations. Spatial measures of within-population local density may provide substantial additional insight to temporal metrics based on population size, and investigating them more widely could be revealing.

Exposure to environmentally transmitted parasites should increase with population density due to accumulation of infective parasites in space. However, resource competition also increases with density, lowering immunity and increasing susceptibility, offering an alternative pathway for density-dependent infection. To test the relationships between these two processes and parasitism, we examined associations between host density, resource availability, immunity, and counts of 3 common helminth parasites using a long-term study of red deer. We found evidence that immunity increased with resource availability while parasite counts declined with immunity. We also found that greater density correlated with reduced resource availability, and while density was positively associated with both strongyle and tissue worm burdens, resource availability was independently and negatively associated with the same burdens. Our results support separate roles of density-dependent exposure and susceptibility in driving infection, providing evidence that resource competition is an important driver of infection, exacerbating effects of density-dependent increases in exposure.

Following the recent report of strongyloidiasis caused by Strongyloides fuelleborni within a semi-captive colony of baboons in a UK safari park, we investigated the genetic relationships of this isolate with other Strongyloides isolates across the world. Whole-genome sequencing data were generated with later phylogenetic analysis of mitochondrial (mt) cytochrome oxidase subunit 1 (cox1) and nuclear ribosomal 18S sequences against 300 published Strongyloides reference genotypes. The putative African origin of the UK S. fuelleborni was confirmed and full-length mt genome sequences were assembled to facilitate a more detailed phylogenetic analysis of 14 mt coding regions against all available Strongyloides species. Our analyses demonstrated that the UK isolate represented a novel African lineage not previously described. Additional complete mt genomes were assembled for several individual UK safari park worms to reveal a slightly altered mt genome gene arrangement, allowing clear separation from Asian S. fuelleborni. Furthermore, these UK worms possessed expanded intergenic regions of unknown function that increase their mt genome size to approximately 24 kilobases (kb) as compared with some 16 kb for Asian S. fuelleborni; this may have arisen from unique populational founder and genetic drift effects set within the peculiar mixed species baboon and drill ancestry of this semi-captive primate colony. A maximum likelihood phylogeny constructed from 14 mt coding regions also supported an evolutionary distinction between Asian and African S. fuelleborni.

We investigated the effects of body mass, geographic range size, the within-range richness of host assemblages (diversity field) and the habitat breadth of small mammalian hosts from 6 biogeographic realms on the species richness of their flea and gamasid mite faunas. We also tested whether the probability of between-host ectoparasite sharing is related to host phylogenetic relatedness, trait similarity or geographic distance/environmental dissimilarity between their ranges. We asked whether the effects of host-associated determinants of ectoparasite richness and the probability of ectoparasite sharing differ between (1) biogeographic realms and (2) fleas and mites. Whenever significant effects of host body mass on ectoparasite richness were found, they were negative, whereas the significant effects of geographic range size, diversity field and habitat breadth were positive. The occurrence of each determinant’s effects on ectoparasite species richness differed (1) within fleas or mites between realms and (2) between fleas and mites within a realm. In all realms, the probability of a flea or a mite species being shared between hosts decreased with a decrease in the hosts’ phylogenetic relatedness, trait similarity, geographic distance between ranges or environmental similarity. The probabilities of an ectoparasite species being shared between hosts were most strongly related to the hosts’ trait similarity and were least related to the environmental similarity. We conclude that caution is needed in making judgements about the generality of macroecological patterns related to parasites based on the investigations of these patterns in limited numbers of localities and when pooling data on various taxa.