Freshwater parasitic copepods appear to exhibit great taxonomic diversity. However, little is known about gene flow between species or whether there is incongruence between morphological and phylogenetic species definitions. Additionally, little is known about what evolutionary factors may contribute to speciation across various lineages. The copepod genus Salmincola, which includes common ectoparasites of fishes in the family Salmonidae, is distributed throughout the northern hemisphere and is a good model to demonstrate limited taxonomic understanding. Much of the regular scholarly output regarding Salmincola copepods comes from fisheries management agencies, where they are considered a pest species. Within a geographic region, Salmincola copepods of the same species are often found infecting their hosts at substantially different rates across different water bodies. However, present taxonomic definitions of Salmincola are based on decades old morphological descriptions, which were limited in geographic scope and number of specimens examined. There is a strong possibility that traditional species definitions in this genus, based on host species along with morphology, are missing cryptic diversity that may explain differences in infection intensity across environments. This review outlines the current scientific limitations of understanding of this genus and provides suggestions for how adding genetic data could inform taxonomic revisions, as well as clarifying connections between genetic differentiation and infection dynamics across localities.

Myxozoans are parasitic cnidarians that can cause severe damage to fish, resulting in economic losses to aquaculture and fisheries. In Israel, only a few taxonomic studies have been conducted on Myxozoa infecting freshwater fish and none on barb parasites. Here, we describe two new myxozoan species – Myxidium grauri n. sp. and Myxidium sharmai n. sp. – from the gallbladder of the barbs Carasobarbus canis and Luciobarbus longiceps, respectively, from the Sea of Galilee (Lake Kinneret). The prevalence of infection was 42.2% (19/45) for M. grauri n. sp. and 25% (5/20) for M. sharmai n. sp. We obtained 18S rRNA sequences for both species, providing the first molecular data on Myxidium infecting barbs from the Sea of Galilee. Phylogenetic analysis confirmed that the genera Myxidium and Zschokkella are not monophyletic. The δ-statistic was used to assess the phylogenetic signal of categorical traits within the Biliary Tract Clade IV lineage, which includes the species studied. The analysis revealed a significant phylogenetic signal associated with the host clade, the parasite’s geographic origin and the type of environment it inhabits. However, some of these statistical results may be influenced by sampling bias, as Percomorpha and Otomorpha fish are disproportionately represented in marine and freshwater environments, respectively. The newly obtained sequences form a distinct lineage within a clade of freshwater-infecting myxozoans. Our findings suggest that myxozoan infections are widespread in the Sea of Galilee. Given their potential impact on fisheries and the lake’s ecosystem, further research is needed to assess their distribution, dynamics and ecological consequences.

Zoonotic parasites associated with domestic dogs have been well-studied in the majority of Europe. In the Balkan region, however, there is minimal knowledge of the parasites in dogs in shelters for rehoming in other European countries. This study aimed to investigate parasitic infections in dogs from two private shelters in Pristina, Kosovo. Faecal samples were collected, representing both adult dogs (72%) and puppies (28%). Coproscopic analysis revealed that 88% of dogs were infected with at least one parasite, with hookworms being the most common. Amplicon metabarcoding targeting internal transcribed spacer (ITS)-2 rRNA gene confirmed the presence of only Uncinaria stenocephala in 68% of samples apparently susceptible to benzimidazoles. The canonical F167Y and Q134H isotype-1 β-tubulin of U. stenocephala mutations conferring benzimidazole resistance were not detected. No evidence of Ancylostoma caninum was detected. Molecular analysis confirmed Giardia duodenalis in 18% of samples, with assemblages B, D and C detected. Other parasites detected included Cystoisospora spp. (18%), Toxocara canis (4%), Toxascaris leonina (6%), Trichuris vulpis (32%), Eucoleus aerophilus (10%) and Dipylidium caninum (2%). Co-infections were identified in 48% of the samples. These findings demonstrate a high frequency of gastrointestinal parasites in shelter dogs. The presence of U. stenocephala and T. vulpis points to the challenges with monitoring and managing these parasitic infections in such settings, as these are likely translocated with the rehomed dogs. The frequency of detection of hookworms emphasizes the need for further research into the distribution of hookworms in Europe because of the emerging benzimidazole resistance on other continents.

Accurate characterization of helminth communities in amphibian hosts is essential for understanding host-parasite dynamics in changing environments. This study presents an integrative parasitological survey of Bufotes viridis populations in eastern Slovakia, using both morphological and molecular methods. A total of 61 road-killed individuals collected across 13 localities were examined for helminth presence. Only nematodes were detected, encompassing 3 families, Rhabdiasidae, Molineidae and Cosmocercidae. Four nematode species were recorded, Rhabdias rubrovenosa, Oswaldocruzia filiformis, O. ukrainae and Aplectana linstowi, and a further unidentified Cosmocerca species. Notably, R. rubrovenosa seems to be a new or previously misidentified helminth species found in Slovakia. Cosmocercidae represented the most abundant family, while Molineidae occurred scarcely. Each species was characterized genetically – for the members of Rhabdiasidae and Cosmocercidae, partial 18S rDNA, complete ITS1, complete 5.8S rRNA, complete ITS2 and partial 28S rDNA sequences were amplified, whereas for representatives of Molineidae, partial COI sequences were obtained. These results underscore the utility of combining molecular and morphological tools in helminth biodiversity studies and provide updated baseline data on nematode infections in B. viridis within an anthropogenically influenced landscape. Despite visual patterns indicating differences in the community compositions of nematode families between urban and rural localities, multivariate analyses testing revealed no significant differences.

A new genus and species of trematode, Paratestophis gelicolus gen. nov., sp. nov., is described from the large intestine of the rainbow water snake, Enhydris enhydris, collected from several provinces in southern Thailand. Morphological analyses reveal distinct characteristics that differentiate P. gelicolus gen. nov., sp. nov. from related echinochasmid taxa, specifically its elongated bottle-shaped body, presence of 22 collar spines, parallel testes and parasitism of snakes–features not observed in other echinochasmid genera. Multi-marker phylogenetic analyses (28S rRNA, 18S rRNA, ITS2 and COI) strongly support its taxonomic placement within Echinochasmidae while confirming its genetic distinction from known genera such as Echinochasmus, Stephanoprora, and Microparyphium, thereby warranting the establishment of Paratestophis gen. nov. The species exhibited a 24% prevalence of infection (25/106) in E. enhydris, and was found co-infecting with four other helminths, including Tanqua siamensis, Encyclometra bungara, and two additional trematode species currently under examination, all occupy distinct ecological niches. Principal Component Analysis based on 19 morphological characters revealed morphological homogeneity among the specimens. This study represents the first record of a new genus and species within Echinochasmidae infecting snakes, and provides an updated systematic framework for the family, including a revised key to genera. The findings emphasise the need for further research into parasite taxonomy, host specificity and evolutionary relationships in Southeast Asian ecosystems.

Intensive rearing of farmed fish may risk disease spillover into free-living populations. This study concerns the blood-feeding gill monogenean of salmonids, Discocotyle sagitatta, on the Isle of Man, UK. Heavy infections in 2 fish farms have led to severe disease with periodic mass mortality. Infection levels in rainbow trout (Oncorhynchus mykiss, overall n = 556) increased with age (i.e. years exposed): by year 3, prevalence was 100%, mean intensity c. 100 (maximum 1150) worms/host. Output from farms of many millions of parasite eggs/day has the potential for transmission to downstream populations of free-living trout. Infections of Discocotyle sagittata were recorded in 132 brown trout and 49 sea trout (Salmo trutta) at 9 sites in rivers associated with or independent of the farms. Its occurrence in all 5 rivers studied confirmed that it is endemic on the Isle of Man irrespective of the farms. Wild brown and sea trout in rivers local to the farms (Rivers Corrany and Neb) had similar burdens to fish from independent drainage systems (Rivers Laxey, Santon and Sulby), and all burdens were within the range reported for other free-living populations in the distribution of D. sagittata. Low worm burdens in brown trout persisted even where these occurred in farm ponds contiguous with heavily infected rainbow trout. It had seemed predictable that high worm burdens in the farms would increase infection in downstream wild fish, but no elevation was detectable. Instead, this and other studies indicate that brown trout develop protective immunity despite intensive re-infection from rainbow trout, preventing pathogenic disease.

Coccidia (Apicomplexa) may have a devastating effect on captive reptiles, particularly chameleons and bearded dragons (Pogona vitticeps). This study investigated the potential of three common feeder insects – the Argentine cockroach (Blaptica dubia), the banana cricket (Gryllus assimilis) and the superworm larva (Zophobas morio) – to act as passive vectors for coccidian oocysts, specifically Isospora amphiboluri and Choleoeimeria pogonae, common enteric parasites of captive bearded dragons. Faecal samples from experimentally infected bearded dragons were fed to the insects to assess the passage of viable oocysts through their digestive tracts. Gryllus assimilis exhibited the highest passage rates for both coccidia, followed by B. dubia; Z. morio showed the lowest rates. However, only G. assimilis passed both I. amphiboluri and C. pogonae at a significantly higher rate than Z. morio. These findings suggest that feeder insects, particularly crickets, can act as mechanical vectors for coccidia, highlighting the importance of strict hygiene protocols in reptile keeping minimizing the risk of parasite transmission.

Parasitic nematodes within Onchocercidae are a diverse group transmitted by hematophagous arthropods. This study investigated the molecular occurrence of filarioid nematodes in 93 wild mammals from the Amazon, Cerrado and Pantanal biomes in Brazil, based on the analysis of the mitochondrial genes 12S ribosomal DNA gene (12S rDNA) and cytochrome c oxidase subunit I gene (COI). Conventional polymerase chain reaction (cPCR) targeting the 12S rDNA gene yielded positive results in 14·44% (13/93) of the samples, including 9·86% of jaguars (7/71), 50% of pumas (1/2), 12·5% of giant anteaters (1/8), 50% of ocelots (1/2) and 60% of crab-eating foxes (3/5). Among the 12S-positive samples, 46% (6/13) also tested positive for the COI gene; however, only 1 sequence was suitable for further analysis. Phylogenetic analyses based on 12S gene sequences revealed 4 distinct lineages within the family Onchocercidae. Groups Ia and Ib, composed of Cerrado and Pantanal sequences from jaguars, formed sister clades to Brugia pahangi and Malayfilaria sofiani, respectively. The sequence from the giant anteater (Group Ic) was more divergent, forming a sister clade to species of the genera Malayfilaria, Wuchereria, and Brugia. Group II included sequences closely related to Dirofilaria immitis and D. striata, encompassing samples from crab-eating foxes, ocelots and a puma. These findings suggest that several wild mammal species may serve as reservoirs for previously uncharacterized Onchocercidae nematodes. Our findings expand the existing knowledge on host associations of filarioid nematodes infecting wild mammals from the Pantanal, the Cerrado and the Amazon Rainforest.