Marine ecosystems are increasingly affected by anthropogenic stressors, including trace elements (TE), highlighting the need for sensitive bioindicators. Fish parasites have proven to be effective bioindicators for TE accumulation, while information on TE levels in parasites of marine mammals remains scarce. The present study combined measurements of TE levels in parasites of fish and mammals. We investigated different developmental stages of the same nematode species, Anisakis simplex, in their different hosts with trophic interactions of larval and adult stages from their respective hosts, the North Sea herring (Clupea harengus) and harbour seals (Phoca vitulina), sampled in the North Sea. Both larval and adult A. simplex accumulated selected TE at higher levels than their hosts, particularly non-essential elements in seals, resulting in high bioconcentration factors. Adult A. simplex exhibited significantly higher concentrations of several essential elements compared to the larval stages, except for Ag, which was accumulated at higher levels in larvae. Stable isotope analysis revealed a consistently lower level of δ[15]N in both larval and adult A. simplex relative to host tissues. This pattern suggests that adult A. simplex may not primarily feed on host tissues and may instead rely partly on host metabolites, such as ingested food items in the seal stomach. Moreover, elevated δ[13]C indicates the utilization of distinct carbon sources by the parasites compared to their hosts. These results indicate that TE accumulation in A. simplex is influenced by both developmental stage and host species, supporting their value as stage-specific bioindicators in marine pollution monitoring.

This study aims to determine the prevalence of infection by larvae from the Anisakidae family in fish commonly consumed in the north of Chile. Then, 2968 specimens belonging to 22 different fish genera were studied. Anisakis spp. third-stage larvae were collected and used for PCR and proteomics studies. Trachurus murphyi was the most parasitized species (51.6%), whereas Scomber japonicus (21.3%) and Isacia conceptions (9.5%) were also found parasitized. PCR studies showed that the only species detected was Anisakis simplex. By LC-MS/MS, we identified a total of 8119 peptide precursors, which correspond to 1919 proteins. Gene Ontology analysis indicated that, among molecular functions, catalytic and binding activities were the most highly expressed. Among biological processes, cellular and metabolic processes were the most highly expressed, while among cellular components, cellular anatomical entities and complex-containing proteins were the most highly detected. By in silico analyses, novel putative allergens were detected through comparative analyses with related genera. Among them, apolipophorin is proposed as a potential new allergen. These findings are of relevance for advancing the understanding of allergen-host immune system interactions. Proteomics and bioinformatics studies strongly suggest that A. simplex is a mosaic of allergens whose implications for public health must be properly evaluated. Finally, a One Health approach is proposed to mitigate Anisakidae infections by integrating multisectoral prevention across human and animal interfaces while concurrently preserving aquatic ecosystem integrity.

Anisakis spp are parasitic nematodes that can infect fish during larval stages, and, if consumed by humans, can cause anisakiasis and severe allergic reactions, including anaphylaxis. Here, we generated a 168 Mb genome assembly of A. simplex, the most abundant species in the Northeast Atlantic, which was used to develop SNP resources using a whole genome pooling resequencing strategy. 1,824,098 SNPs and 151,767 short structural variants were identified, showing the high polymorphism and complexity of A. simplex genome. A 481 SNP panel was developed for population screening using the Agriseq technology, through strict filtering and homogeneous distribution across the genome. This panel was used for genotyping 823 larvae and adults of A. simplex, 775 A. pegreffii and 402 putative hybrids collected from different hosts across the Northeast Atlantic, 275 SNPs being consistently genotyped in both species. Among them, 10 SNPs showing extreme genetic differentiation between A. simplex and A. pegreffii and no linkage disequilibrium in A. simplex, were used to design a cost-effective SNP tool for species and hybrid identification in population surveys. The genomic resources obtained will facilitate efficient surveillance programs, accurate discrimination of species and hybrids, effective anisakiasis management in fisheries, and improved seafood safety.

The consumption of raw or undercooked fish has increased concerns regarding zoonotic parasites, particularly nematode larvae of the genus Anisakis. This study investigates the epidemiology of anisakid infections in commercially important fishes from Portuguese coastal waters, focusing on spatial and seasonal patterns. A total of 538 specimens of five fish species (Trachurus trachurus, Scomber colias, Scomber scombrus, Merluccius merluccius, and Sardina pilchardus) were collected from six localities during winter and summer 2024. Parasites were recovered from viscera and muscles by pepsin digestion, identified using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) targeting the internal transcribed spacer (ITS) region, and confirmed by sequencing. Generalized linear models were applied for data analysis. All species were infected with Anisakis spp. larvae, with significant differences among host species, host size, seasons, and regions. Most larvae were in the viscera (90.5-100%), with a smaller proportion in muscles. Trachurus showed the highest infection levels (45-100% prevalence; mean intensity up to 161 larvae per infected host). Molecular analysis of 424 larvae identified Anisakis pegreffii (56.6%) as the dominant species, followed by A. simplex (sensu stricto) (30.9%), putative hybrids (12.3%), and a single Skrjabinisakis physeteris larva. A significant north-south and seasonal gradient was observed, with A. simplex (s.s.) predominating in northern and winter samples, particularly in the muscles. These results suggest geographical and seasonal variations in Anisakis spp. distribution. Despite potential sampling bias, the presence of zoonotic species in fish muscles highlights the need for strict post-capture handling, freezing, and cooking practices to reduce consumer risk.

The relationship between the anisakid nematode Anisakis simplex and red vent syndrome (RVS) was investigated through parasitological, clinical and pathological examinations of 124 wild adult Atlantic salmon Salmo salar, sampled from the River Dee, Wales, River Tyne, England, and River Tyne estuary between 2009 to 2013. All S. salar were infected with A. simplex, but those exhibiting RVS lesions displayed significantly higher infection intensities of A. simplex than unaffected individuals. S. salar exhibiting RVS lesions also displayed significantly higher infection intensities of A. simplex in the discrete location of the vent than unaffected fish. Up to 95% of total A. simplex infection intensities were found within the vent, with up to 83.6% localised within the outer ~5-10 mm of vent tissue. This suggests that the vent is a discrete and potentially favoured site of A. simplex. Intensity of infection of A. simplex in the vent did not always correlate with vent pathology. Moreover, internal inflammation and marked fibrogranulomatous changes were observed in the absence of associated haemorrhage, suggesting that visual reddening of the vent may not always occur in spite of significant A. simplex infections. Whilst fish exhibiting clinical RVS displayed significantly higher vent infection intensities, no correlation was identified between the severity of symptoms and A. simplex intensity.

Allergic anisakiasis (AA), caused by the ingestion of fish contaminated with Anisakis larvae, has emerged as a growing global health concern due to the increasing consumption of raw or undercooked seafood. Anisakis simplex is identified as the primary etiologic species, responsible for gastrointestinal symptoms, IgE-mediated (Type I) or cell-mediated (Type IV) manifestations, and gastro-allergic anisakiasis (GAA), a unique clinical overlap between parasitic infection and acute IgE-mediated food allergy. In this review, we analyzed the epidemiology of Anisakis simplex allergy, the main diagnostic methods to confirm a diagnosis of food allergy, its clinical manifestations, and how these differ in different countries around the world. This multidisciplinary synthesis provides, for the first time, an integrated understanding of Anisakis-induced disease mechanisms across human, animal, and cellular levels. The persistence of allergenic proteins despite standard food processing underscores the need for improved diagnostic tools, public health surveillance, and preventive strategies-particularly in populations with high seafood consumption or occupational exposure. A comprehensive approach combining clinical, molecular, and immunological perspectives is essential to address the expanding global burden of allergic anisakiasis.

Marine nematodes are important food-borne parasites infecting many species of marine fish and cephalopods. This review provides a comprehensive discussion of the food safety concerns associated with marine nematodes in seafood, along with emerging methods for their detection. The potential prevention strategies for these seafood-borne parasites were also explored. According to the results, anisakiasis is the most serious nematode disease humans acquire from marine fish, chiefly due to Anisakis simplex larvae and, to a lesser degree, Pseudoterranova decipiens. Several analytical methods are employed for the detection of marine nematodes in seafood, each characterized by its own set of advantages and drawbacks. While traditional visual and digestion-based methods are still employed, newer techniques like hyperspectral imaging and molecular analysis are advancing the field. These innovations provide greater sensitivity, automation, and the ability to identify parasites at the species level. The safety and quality of seafood products are ensured through the application of methods including freezing, salting, pulsed electric fields and high hydrostatic pressure. The effectiveness of these methods depends on the processing technique, nematode species, and parasite's developmental stage. This review presents findings pertinent to seafood safety that will be of significant interest to both the research community and the industrial sector.

Marine nematodes of the genus Anisakis are shaped by complex life cycles and heterogeneous marine environments, yet the molecular basis of their developmental and population differentiation remains poorly understood. Here, we analyzed mRNA and long non-coding RNA expression in third- and fourth-stage larvae of Anisakis simplex (s. s.) collected from the Baltic Sea and the Northeast Atlantic using high-throughput RNA sequencing. Larval development was associated with extensive transcriptional remodeling involving cuticle organization, metabolism, proteolysis, and host-interaction pathways. Comparisons between populations revealed pronounced geographic divergence, including population-specific gene expression and reversal patterns shared across developmental stages. A subset of long non-coding RNAs was linked to the regulation of developmentally and population-biased genes, targeting pathways related to energy metabolism, ion transport, and protein synthesis. These findings demonstrate that developmental progression and geographic origin jointly shape the transcriptomic architecture of Anisakis simplex (s. s.), providing insight into molecular mechanisms underlying parasite adaptation with potential relevance for ecology, evolution, and anisakiasis risk.

Grey seals, Halichoerus grypus (GSs), inhabit cold temperate and subarctic waters along the North Atlantic Ocean. Individuals of GS can regularly disperse towards southern areas (ca. 38°N-39°N) but occurrence at lower latitudes is exceptional. On 18 February 2022, a 217-cm-long male of GS was detected in waters off the SW Atlantic coast of Spain (37°N), then entered the western Mediterranean Sea and wandered for 15 days until he died. Here, we use gastrointestinal parasites to investigate the geographical origin of the GS and the length of the journey towards Mediterranean waters. Seven helminth taxa were found, namely, the digeneans Ascocotyle septentrionalis and Cryptocoyle lingua, the nematodes Contracaecum osculatum s.s., Anisakis simplex s.s., and A. pegreffii, and the acanthocephalans Corynosoma sp.1 and C. magdaleni (= strumosum) or C. nortmeri. The parasite composition closely resembles that reported in native harbour seals (Phoca vitulina) of the Wadden Sea (ca. 51°-55°N), from where A. septentrionalis is apparently endemic. Considering that (i) A. septentrionalis cannot be acquired out of the Wadden Sea, and (ii) the lifespan and population structure of the parasites found, we infer that the GS came from waters near the Wadden Sea, and the length of the journey was ca. 1 month, with presumably little ingestion of (parasitized) food. To our knowledge, this is the first study using parasites to unveil the geographical mobility of pinnipeds.

Essential oils, natural volatile products extracted from aromatic plants, exhibit a wide range of biological activities, including antimicrobial and antiparasitic properties. Anisakis simplex is a parasitic nematode commonly found in marine fish, which poses a significant health risk to humans through the consumption of raw or undercooked seafood, leading to anisakiasis, a zoonotic disease with both gastrointestinal and allergic manifestations. In this study, the impact of Crithmum maritimum L. (Apiaceae) essential oil on this nematode was evaluated in vitro. The chemical composition of C. maritimum essential oil was determined by gas chromatography-mass spectrometry (GC-MS). The analysis revealed γ-terpinene, limonene, and sabinene as the major components. The nematicidal activity, larval penetration ability, resistance to acidic pH, and inhibition of acetylcholinesterase were evaluated. The essential oil effects on interleukin production and cytotoxicity in HepG2 and Caco-2 cells were also assessed. C. maritimun exhibited larvicidal activity, with LD₅₀ values of 619.11 μg mL-1 at 24 h and 353.95 μg mL-1 at 48 h. Additionally, it showed no significant cytotoxicity in HepG2 and Caco-2 cell lines at the concentrations tested. In Caco-2 cells stimulated with crude Anisakis extract, the essential oil modulated interleukin production. Furthermore, it demonstrated in vitro inhibitory activity against 5-lipoxygenase and phospholipase A₂, with IC₅₀ values of 99.35 and 253.31 μg mL-1, respectively. The traditional culinary use of C. maritimum, together with the observed anti-Anisakis activity in our study, suggest this essential oil may offer a promising complementary approach within broader integrated food safety strategies, especially in Anisakis control.

The sambaqui (shellmounds) people are recognized as fisher-gatherers who inhabited the coastal regions of Brazil, with a subsistence on a diet composed of fish, molluscs, and plants. Paleoparasitological investigations in these open-air sites are challenged by the severe taphonomic processes affecting parasite vestige preservation. Previous palaeogenetic work reported parasite helminth infection by Ascaris sp. in an individual from Jabuticabeira II (JABII) sambaqui, located in the Santa Catarina state, Brazil (2890 ± 55 to 1805 ± 65 years BP). To expand our knowledge about helminth infections in sambaqui people, this study applied a palaeogenomics approach in JABII. Sediments from pelvic and sacral regions of 3 JABII individuals and environmental samples underwent ancient DNA extraction and cox1 gene PCRs. High-throughput sequencing data were compared to a custom-built reference database. The JABII dataset revealed reads that are mapped against plathelminth and nematode parasites. Plathelminth observations are probably attributable to pseudo-parasitism and are associated with the animal hosts identified within the JABII faunal assemblages. Two JABII individuals exhibited Anisakis simplex, Contracaecum osculatum, and Ascaris sp. Anisakids are common parasites of marine fish, crustaceans, and mammals that infect humans by consuming fish. Most of the fish identified at the JABII site are currently documented as being infected by Anisakidae. Ascaris sp. is verified in different JABII individuals from the previous study, confirming the spread of this soil-transmitted helminthiasis. The novel data herein agree with the subsistence of the JABII fisher-gatherers, the sedentary lifestyle and the faunal surroundings in the Southern coastal region of Brazil.