Tissue-specific transcriptomes of Anisakis simplex (sensu stricto) and Anisakis pegreffii reveal potential molecular mechanisms involved in pathogenicity

Re-evaluation of certain aspects of the EFSA Scientific Opinion of April 2010 on risk assessment of parasites in fishery products, based on new scientific data. Part 1: ToRs1-3

Surveillance data published since 2010, although limited, showed that there is no evidence of zoonotic parasite infection in market quality Atlantic salmon, marine rainbow trout, gilthead seabream, turbot, meagre, Atlantic halibut, common carp and European catfish. No studies were found for greater amberjack, brown trout, African catfish, European eel and pikeperch. Anisakis pegreffii, A. simplex (s. s.) and Cryptocotyle lingua were found in European seabass, Atlantic bluefin tuna and/or cod, and Pseudamphistomum truncatum and Paracoenogonimus ovatus in tench, produced in open offshore cages or flow-through ponds or tanks. It is almost certain that fish produced in closed recirculating aquaculture systems (RAS) or flow-through facilities with filtered water intake and exclusively fed heat-treated feed are free of zoonotic parasites. Since the last EFSA opinion, the UV-press and artificial digestion methods have been developed into ISO standards to detect parasites in fish, while new UV-scanning, optical, molecular and OMICs technologies and methodologies have been developed for the detection, visualisation, isolation and/or identification of zoonotic parasites in fish. Freezing and heating continue to be the most efficient methods to kill parasites in fishery products. High-pressure processing may be suitable for some specific products. Pulsed electric field is a promising technology although further development is needed. Ultrasound treatments were not effective. Traditional dry salting of anchovies successfully inactivated Anisakis. Studies on other traditional processes - air-drying and double salting (brine salting plus dry salting) - suggest that anisakids are successfully inactivated, but more data covering these and other parasites in more fish species and products is required to determine if these processes are always effective. Marinade combinations with anchovies have not effectively inactivated anisakids. Natural products, essential oils and plant extracts, may kill parasites but safety and organoleptic data are lacking. Advanced processing techniques for intelligent gutting and trimming are being developed to remove parasites from fish.

Fecundity, in vitro early larval development and karyotype of the zoonotic nematode Anisakis pegreffii

The in vitro life cycle of zoonotic helminths is an essential tool for -omic translational studies focused on disease control and treatment. Anisakiosis is an emerging zoonosis contracted by the ingestion of raw or undercooked fish infected with the third stage larvae (L3) of two sibling species Anisakis simplex sensu stricto (s.s.) and Anisakis pegreffii, the latter being the predominant species in the Mediterranean basin. Recently, in vitro culture of A. pegreffii has been developed to enable fast and large-scale production of fertile adults. However, the conditions for larval development from hatching to infective L3 were not fulfilled to complete the cycle. Herein, we used a Drosophila medium supplemented with chicken serum and adjusted different osmolarities to maintain the culture of L3 hatched from eggs for up to 17 weeks. The highest survival rate was observed in the medium with the highest osmolarities, which also allowed the highest larval exsheathment rate. Key morphological features of embryogenesis and postembryogenesis studied by transmission electron microscopy revealed that the excretory gland cell is differentiated already up to 48 h post-hatching. Extracellular vesicles and cell-free mitochondria are discharged between the two cuticle sheets of the second stage larvae (L2). Contemporarly cultivated, two populations of adult A. simplex s.s. and A. pegreffii reached an average production of 29,914.05 (± 27,629.36) and 24,370.96 (± 12,564.86) eggs/day/female, respectively. The chromosome spreads of A. pegreffii obtained from mature gonads suggests a diploid karyotype formula of 2n = 18. The development of a reliable protocol for the in vitro culture of a polyxenous nematode such as Anisakis spp. will serve to screen for much needed novel drug targets, but also to study the intricated and unknown ecological and physiological traits of these trophically transmitted marine nematodes.

De novo transcriptome assembly of an Antarctic nematode for the study of thermal adaptation in marine parasites

Understanding the genomic underpinnings of thermal adaptation is a hot topic in eco-evolutionary studies of parasites. Marine heteroxenous parasites have complex life cycles encompassing a free-living larval stage, an ectothermic intermediate host and a homeothermic definitive host, thus representing compelling systems for the study of thermal adaptation. The Antarctic anisakid Contracaecum osculatum sp. D is a marine parasite able to survive and thrive both at very cold and warm temperatures within the environment and its hosts. Here, a de novo transcriptome of C. osculatum sp. D was generated for the first time, by performing RNA-Seq experiments on a set of individuals exposed to temperatures experienced by the nematode during its life cycle. The analysis generated 425,954,724 reads, which were assembled and then annotated. The high-quality assembly was validated, achieving over 88% mapping against the transcriptome. The transcriptome of this parasite will represent a valuable genomic resource for future studies aimed at disentangling the genomic architecture of thermal tolerance and metabolic pathways related to temperature stress.

An update and ecological perspective on certain sentinel helminth endoparasites within the Mediterranean Sea

The Mediterranean Sea is recognized as a marine biodiversity hotspot. This enclosed basin is facing several anthropogenic-driven threats, such as seawater warming, pollution, overfishing, bycatch, intense maritime transport and invasion by alien species. The present review focuses on the diversity and ecology of specific marine trophically transmitted helminth endoparasites (TTHs) of the Mediterranean ecosystems, aiming to elucidate their potential effectiveness as ‘sentinels’ of anthropogenic disturbances in the marine environment. The chosen TTHs comprise cestodes and nematodes sharing complex life cycles, involving organisms from coastal and marine mid/upper-trophic levels as definitive hosts. Anthropogenic disturbances directly impacting the free-living stages of the parasites and their host population demographies can significantly alter the distribution, infection levels and intraspecific genetic variability of these TTHs. Estimating these parameters in TTHs can provide valuable information to assess the stability of marine trophic food webs. Changes in the distribution of particular TTHs species can also serve as indicators of sea temperature variations in the Mediterranean Sea, as well as the bioaccumulation of pollutants. The contribution of the chosen TTHs to monitor anthropogenic-driven changes in the Mediterranean Sea, using their measurable attributes at both spatial and temporal scales, is proposed.

Clinical factors associated with acute abdominal symptoms induced by gastric anisakiasis: a multicenter retrospective cohort study

BACKGROUND

Gastric anisakiasis typically causes severe abdominal symptoms; however, we incidentally detected asymptomatic gastric anisakiasis cases during esophagogastroduodenoscopy. The factors associated with developing acute abdominal symptoms induced by gastric anisakiasis remain unclear. Therefore, this study aimed to investigate the clinical factors associated with abdominal symptoms of gastric anisakiasis by comparing symptomatic and asymptomatic cases.

METHODS

This was a retrospective cohort study involving 264 patients diagnosed with gastric anisakiasis at nine hospitals in Japan between October 2015 and October 2021. We analyzed patients' medical records and endoscopic images and compared the clinical factors between the symptomatic and asymptomatic groups.

RESULTS

One hundred sixty-five patients (77.8%) were diagnosed with abdominal symptoms, whereas 47 (22.2%) were asymptomatic. Older age, male sex, diabetes mellitus, gastric mucosal atrophy, and gastric mucosal atrophy of the Anisakis penetrating area were significantly more common in the asymptomatic group than in the symptomatic group. Multivariate analysis revealed that age (p = 0.007), sex (p = 0.017), and presence or absence of mucosal atrophy (p = 0.033) were independent factors for the occurrence of acute abdominal symptoms. In addition, cases that were Helicobacter pylori naïve, with an elevation of white blood cells, or without an elevation of eosinophils were more common in the symptomatic group than in the asymptomatic group.

CONCLUSIONS

Age, sex, and presence or absence of gastric mucosal atrophy were the clinical factors associated with the occurrence of acute abdominal symptoms. Older and male patients and those with gastric mucosal atrophy were less likely to show abdominal symptoms. The mechanisms of the occurrence of symptoms induced by gastric anisakiasis remain unclear; however, our results will help clarify this issue in the future.

Metabolomic analysis reveals a differential adaptation process of the larval stages of Anisakis simplex to the host environment

Introduction: Anisakis simplex are parasitic nematodes that cause anisakiasis. The possibility of infection with this parasite is through consumption of raw or undercooked fish products. A. simplex infections are often misdiagnosed, especially in subclinical cases that do not present with typical symptoms such as urticaria, angioedema, and gastrointestinal allergy. The resulting allergic reactions range from rapid-onset and potentially fatal anaphylactic reactions to chronic, debilitating conditions. While there have been numerous published studies on the genomes and proteomes of A. simplex, less attention has been paid to the metabolomes. Metabolomics is concerned with the composition of metabolites in biological systems. Dynamic responses to endogenous and exogenous stimuli are particularly well suited for the study of holistic metabolic responses. In addition, metabolomics can be used to determine metabolic activity at different stages of development or during growth. Materials and methods: In this study, we reveal for the first time the metabolomes of infectious stages (L3 and L4) of A. simplex using untargeted metabolomics by ultra-performance liquid chromatography-mass spectrometry. Results: In the negative ionization mode (ESI-), we identified 172 different compounds, whereas in the positive ionization mode (ESI+), 186 metabolites were found. Statistical analysis showed that 60 metabolites were found in the ESI- mode with different concentration in each group, of which 21 were more enriched in the L3 larvae and 39 in the L4 stage of A. simplex. Comparison of the individual developmental stages in the ESI + mode also revealed a total of 60 differential metabolites, but 32 metabolites were more enriched in the L3 stage larvae, and 28 metabolites were more concentrated in the L4 stage. Discussion: The metabolomics study revealed that the developmental stages of A. simplex differed in a number of metabolic pathways, including nicotinate and nicotinamide metabolism. In addition, molecules responsible for successful migration within their host, such as pyridoxine and prostaglandins (E1, E2, F1a) were present in the L4 stage. In contrast, metabolic pathways for amino acids, starch, and sucrose were mainly activated in the L3 stage. Our results provide new insights into the comparative metabolome profiles of two different developmental stages of A. simplex.

Basophil Activation Test in the Diagnosis of Anisakis Allergy: An Observational Study from an Area of High Seafood Consumption in Italy

The rising popularity of undercooked or raw seafood containing larvae of the Anisakis parasite has led to issues of public health concern due to allergic manifestations. We conducted an observational study on the use of an innovative Anisakis allergy diagnostic algorithm in a convenience sample of 53 allergic outpatients recruited in Western Sicily, between April 2021 and March 2022. We included individuals with an anamnesis suggestive of IgE sensitization to Anisakis reporting clinical manifestation in the last month due to allergic reactions after eating fresh fish, or in subjects at high exposure risk with sea products while abstaining from fish ingestion, excluding those with documented fish sensitization. Outpatients were tested via Skin Prick Test, IgE-specific dosage and Basophil Activation Test (BAT). Twenty-six outpatients were diagnosed with Anisakis, while 27 with Chronic Urticaria (CU). We found a seven-fold excess risk for Anisakis (p4) positivity in the Anisakis allergic outpatients, as compared to the CU ones. BAT showed the best diagnostic accuracy (92.45%) and specificity (100%), while specific IgE to Ascaris (p1) documented the best sensitivity (92.31%) but a very low specificity (37.04%). In conclusion, our findings may represent a potentially useful contribution to the future development of updated clinical guidelines.

Proteomic characterization of extracellular vesicles released by third stage larvae of the zoonotic parasite Anisakis pegreffii (Nematoda: Anisakidae)

Introduction

Anisakis pegreffii is a sibling species within the A. simplex (s.l.) complex requiring marine homeothermic (mainly cetaceans) and heterothermic (crustaceans, fish, and cephalopods) organisms to complete its life cycle. It is also a zoonotic species, able to accidentally infect humans (anisakiasis). To investigate the molecular signals involved in this host-parasite interaction and pathogenesis, the proteomic composition of the extracellular vesicles (EVs) released by the third-stage larvae (L3) of A. pegreffii, was characterized.

Methods

Genetically identified L3 of A. pegreffii were maintained for 24 h at 37°C and EVs were isolated by serial centrifugation and ultracentrifugation of culture media. Proteomic analysis was performed by Shotgun Analysis.

Results and discussion

EVs showed spherical shaped structure (size 65-295 nm). Proteomic results were blasted against the A. pegreffii specific transcriptomic database, and 153 unique proteins were identified. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis predicted several proteins belonging to distinct metabolic pathways. The similarity search employing selected parasitic nematodes database revealed that proteins associated with A. pegreffii EVs might be involved in parasite survival and adaptation, as well as in pathogenic processes. Further, a possible link between the A. pegreffii EVs proteins versus those of human and cetaceans’ hosts, were predicted by using HPIDB database. The results, herein described, expand knowledge concerning the proteins possibly implied in the host-parasite interactions between this parasite and its natural and accidental hosts.

De novo transcriptome assembly and annotation of the third stage larvae of the zoonotic parasite Anisakis pegreffii

OBJECTIVES

Anisakis pegreffii is a zoonotic parasite requiring marine organisms to complete its life-history. Human infection (anisakiasis) occurs when the third stage larvae (L3) are accidentally ingested with raw or undercooked infected fish or squids. A new de novo transcriptome of A. pegreffii was here generated aiming to provide a robust bulk of data to be used for a comprehensive "ready-to-use" resource for detecting functional studies on genes and gene products of A. pegreffii involved in the molecular mechanisms of parasite-host interaction.

DATA DESCRIPTION

A RNA-seq library of A. pegreffii L3 was here newly generated by using Illumina TruSeq platform. It was combined with other five RNA-seq datasets previously gathered from L3 of the same species stored in SRA of NCBI. The final dataset was analyzed by launching three assembler programs and two validation tools. The use of a robust pipeline produced a high-confidence protein-coding transcriptome of A. pegreffii. These data represent a more robust and complete transcriptome of this species with respect to the actually existing resources. This is of importance for understanding the involved adaptive and immunomodulatory genes implicated in the "cross talk" between the parasite and its hosts, including the accidental one (humans).

A miRNAs catalogue from third-stage larvae and extracellular vesicles of Anisakis pegreffii provides new clues for host-parasite interplay

Anisakids are widespread marine parasites of medical, veterinary and economic relevance. They infect marine natural hosts but humans can accidentally acquire the fish-borne zoonosis anisakiasis by ingesting infected raw fishes or mollusks. Among the several species described, Anisakis pegreffii is one of the main etiological agent of the disease, in particular in the Mediterranean area. Despite the growing evidence of miRNAs involvement in host-parasite interplay, and the emerging role of exosomal microvesicles in shuttling them between different cell types (and sometime across species), no information on miRNAs from any Anisakis species is presently available. In this study we isolated extracellular vesicles (EVs) released by Anisakis pegreffii infective third-stage larvae (L3) and analyzed by RNA-seq small RNAs from both L3 and EVs. We showed by nanoparticle tracking analysis that L3 release in culture medium particles of size compatible with the one of extracellular vesicles. A catalogue of 156 miRNAs from A. pegreffii was compiled by sequence comparison to evolutionary close species and miRNA prediction software. Using differential expression analysis, we identified a small number of highly abundant miRNAs in larvae and extracellular vesicles fractions whose potential biological relevance may deserve future investigation. Finally, A. pegreffii miRNAs were compared to those described in other parasitic helminths and predicted targets among human genes were searched, suggesting their potential involvement during infection.

Drug efficacy on zoonotic nematodes of the Anisakidae family - new metabolic data

In the Anisakidae family, there are nematodes, most of which are parasitic for important commercial fish species. Both public health risks and socio-economic problems are attributed to these parasites. Despite these concerns, knowledge of the metabolism of these parasites remains unknown. Therefore, the main objective of this study was to investigate the receptors of drugs and oxidative metabolic status of two Anisakidae species, Pseudoterranova decipiens (s. s.) and Contracaecum osculatum (s. s.), under the influence of anthelminthic drugs, ivermectin (IVM) and pyrantel (PYR), at different concentrations: 1.56, 3.125 and 6.25 μg mL⁻¹ of culture medium for 3, 6, 9, 12 and 72 h. The mRNA expressions of the γ-aminobutyric acid receptor, acetylcholine receptor subunits, adenosine triphosphate-binding cassette transporters and antioxidative enzymes were determined. The total antioxidant capacity and glutathione S-transferase activity were also examined. To the best of the authors' knowledge, this is the first time that IVM and PYR have been tested against these parasitic nematodes.

Tandem Mass Tagging (TMT) Reveals Tissue-Specific Proteome of L4 Larvae of Anisakis simplex s. s.: Enzymes of Energy and/or Carbohydrate Metabolism as Potential Drug Targets in Anisakiasis

Anisakis simplex s. s. is a parasitic nematode of marine mammals and causative agent of anisakiasis in humans. The cuticle and intestine of the larvae are the tissues most responsible for direct and indirect contact, respectively, of the parasite with the host. At the L4 larval stage, tissues, such as the cuticle and intestine, are fully developed and functional, in contrast to the L3 stage. As such, this work provides for the first time the tissue-specific proteome of A. simplex s. s. larvae in the L4 stage. Statistical analysis (FC ≥ 2; p-value ≤ 0.01) showed that 107 proteins were differentially regulated (DRPs) between the cuticle and the rest of the larval body. In the comparison between the intestine and the rest of the larval body at the L4 stage, 123 proteins were identified as DRPs. Comparison of the individual tissues examined revealed a total of 272 DRPs, with 133 proteins more abundant in the cuticle and 139 proteins more abundant in the intestine. Detailed functional analysis of the identified proteins was performed using bioinformatics tools. Glycolysis and the tricarboxylic acid cycle were the most enriched metabolic pathways by cuticular and intestinal proteins, respectively, in the L4 stage of A. simplex s. s. The presence of two proteins, folliculin (FLCN) and oxoglutarate dehydrogenase (OGDH), was confirmed by Western blot, and their tertiary structure was predicted and compared with other species. In addition, host–pathogen interactions were identified, and potential new allergens were predicted. The result of this manuscript shows the largest number of protein identifications to our knowledge using proteomics tools for different tissues of L4 larvae of A. simplex s. s. The identified tissue-specific proteins could serve as targets for new drugs against anisakiasis.

Insights into the functional expansion of the astacin peptidase family in parasitic helminths

Helminths secrete a plethora of proteins involved in parasitism-related processes such as tissue penetration, migration, feeding and immunoregulation. Astacins, a family of zinc metalloproteases belonging to the peptidase family M12, are one of the most abundantly represented protein families in the secretomes of helminths. Despite their involvement in virulence, very few studies have addressed the role of this loosely defined protein group in parasitic helminths. Herein, we have analysed the predicted proteomes from 154 helminth species and confirmed the expansion of the astacin family in several nematode taxa. The astacin domain associated with up to 110 other domains into 145 unique domain architectures, where CUB and ShK constitute the principal and nearly independent bi-domain frameworks. The presence of co-existing domains suggests promiscuous adaptable functions to several roles. These activities could be related either to substrate specificity or to higher-order functions, such as anti-angiogenesis and immunomodulation, where the astacin domain would play an accessory role. Furthermore, some phylogenetically restricted mutations in the astacin domain affected residues located at the active cleft and binding sub-pockets, suggesting adaptation to different substrate specificities. Altogether, these findings suggest the astacin domain is a highly adaptable module that fulfils multiple proteolytic needs of the parasitic lifestyle. This study contributes to the understanding of helminth-secreted astacins and, ultimately, provides the foundation to guide future investigations about the role of this diverse family of proteins in host-parasite interactions.

A Complex Proteomic Response of the Parasitic Nematode Anisakis simplex s.s. to Escherichia coliLipopolysaccharide

Helminths are masters at manipulating host's immune response. Especially, parasitic nematodes have evolved strategies that allow them to evade, suppress, or modulate host's immune response to persist and spread in the host's organism. While the immunomodulatory effects of nematodes on their hosts are studied with a great commitment, very little is known about nematodes' own immune system, immune response to their pathogens, and interactions between parasites and bacteria in the host's organism. To illustrate the response of the parasitic nematode Anisakis simplex s.s. during simulated interaction with Escherichia coli, different concentrations of lipopolysaccharide (LPS) were used, and the proteomic analysis with isobaric mass tags for relative and absolute quantification (tandem mass tag-based LC-MS/MS) was performed. In addition, gene expression and biochemical analyses of selected markers of oxidative stress were determined. The results revealed 1148 proteins in a group of which 115 were identified as differentially regulated proteins, for example, peroxiredoxin, thioredoxin, and macrophage migration inhibitory factor. Gene Ontology annotation and Reactome pathway analysis indicated that metabolic pathways related to catalytic activity, oxidation-reduction processes, antioxidant activity, response to stress, and innate immune system were the most common, in which differentially regulated proteins were involved. Further biochemical analyses let us confirm that the LPS induced the oxidative stress response, which plays a key role in the innate immunity of parasitic nematodes. Our findings, to our knowledge, indicate for the first time, the complexity of the interaction of parasitic nematode, A. simplex s.s. with bacterial LPS, which mimics the coexistence of helminth and gut bacteria in the host. The simulation of this crosstalk led us to conclude that the obtained results could be hugely valuable in the integrated systems biology approach to describe a relationship between parasite, host, and its commensal bacteria.

The Selection of Reliable Reference Genes for RT-qPCR Analysis of Anisakis simplex Sensu Stricto Gene Expression from Different Developmental Stages

BACKGROUND

Anisakis simplex s. s. is a parasitic nematode with a complex life cycle in which humans can become accidental hosts by consuming raw or not fully cooked fish containing L3 larvae. The growing popularity of raw fish dishes has contributed to an increase in the incidence of anisakiasis, which has spurred scientific efforts to develop new methods for diagnosing and treating the disease and also to investigate the gene expression at different developmental stages of this parasite. The identification of reference genes suitable for the normalization of RT-qPCR data has not been studied with respect to A. simplex s. s.

METHODS

In the present study, eight candidate reference genes were analyzed in A. simplex s. s. at two different developmental stages: L3 and L4. The expression stability of these genes was assessed by geNorm and NormFinder softwares.

RESULTS

In general, our results identified translation elongation factor 1α (ef-1α) and peptidyl-prolyl isomerase 12 (ppi12) as the most stable genes in L3 and L4 developmental stages of A. simplex s. s. Validation of the selected reference genes was performed by profiling the expression of the nuclear hormone receptor gene (nhr 48) in different developmental stages.

CONCLUSIONS

This first analysis selecting suitable reference genes for RT-qPCR in A. simplex s. s. will facilitate future functional analyses and deep mining of genetic resources in this parasitic nematode.

Expression and functionality of allergenic genes regulated by simulated gastric juice in Anisakis pegreffii

To better understand the molecular mechanisms underlying allergens and parasite immunity and discover the stage-enriched gene expression of fish-borne zoonotic nematodes in the stomach, we used RNA-seq to study the transcriptome profiles of Anisakis pegreffii (Nematoda: Anisakidae, AP) in simulated gastric juice. Mobile L3 larvae were incubated in simulated medium at 37 °C in 5% CO₂ (AP-GJ) and the control group larvae were collected in PBS under the same conditions (AP-PBS). We found that the sequences of A. pegreffii were highly similar to Toxocara canis sequences. Among the transcripts, there would be 138 up-regulated putative genes and 251 down-regulated putative genes in AP-GJ group. Several lipid binging-related genes were more highly expressed in AP-GJ larvae. Moreover, 17 allergen genes were up-regulated and 29 were down-regulated in AP-GJ larvae. Eleven allergen genes belonged to one or more of the following three categories: biological process, cellular component, and molecular function. According to KEGG analysis, the main pathways that were represented included protein processing in transcription, immune system, cancer, and infectious disease. In particular, the most significant changes in the expression of parasite-derived allergen products occurred in AP-GJ larvae. This study helps us to extend our understanding of the biology of the fish-borne zoonotic parasite A. pegreffii and could be helpful for more precise risk assessment and providing guidelines for allergic consumers.

Quantitative Proteomics Comparison of Total Expressed Proteomes of Anisakis simplex Sensu Stricto, A. pegreffii, and Their Hybrid Genotype

The total proteomes of Anisakis simplex s.s., A. pegreffii and their hybrid genotype have been compared by quantitative proteomics (iTRAQ approach), which considers the level of expressed proteins. Comparison was made by means of two independent experiments considering four biological replicates of A. simplex and two each for A. pegreffii and hybrid between both species. A total of 1811 and 1976 proteins have been respectively identified in the experiments using public databases. One hundred ninety-six proteins were found significantly differentially expressed, and their relationships with the nematodes' biological replicates were estimated by a multidimensional statistical approach. Results of pairwise Log2 ratio comparisons among them were statistically treated and supported in order to convert them into discrete character states. Principal component analysis (PCA) confirms the validity of the method. This comparison selected thirty seven proteins as discriminant taxonomic biomarkers among A. simplex, A. pegreffii and their hybrid genotype; 19 of these biomarkers, encoded by ten loci, are specific allergens of Anisakis (Ani s7, Ani s8, Ani s12, and Ani s14) and other (Ancylostoma secreted) is a common nematodes venom allergen. The rest of the markers comprise four unknown or non-characterized proteins; five different proteins (leucine) related to innate immunity, four proteolytic proteins (metalloendopeptidases), a lipase, a mitochondrial translocase protein, a neurotransmitter, a thyroxine transporter, and a structural collagen protein. The proposed methodology (proteomics and statistical) solidly characterize a set of proteins that are susceptible to take advantage of the new targeted proteomics.

Anisakiasis and Anisakis: An underdiagnosed emerging disease and its main etiological agents

Anisakiasis or anisakiosis is a human parasitic infection caused by the third-stage larvae (L3) of nematodes of the genus Anisakis, although the term is also used in medical literature for the much less frequent (<3% of cases) infection by L3 of other genera of anisakids, particularly Pseudoterranova. These parasites have a marine lifecycle. Humans are infected by the L3 through ingesting of fish and squid, the intermediate/paratenic hosts. The live larvae generally penetrate the wall of the stomach or intestine causing, among other symptoms, intense pain or allergic symptoms. These are emerging, cosmopolite illnesses. Diagnosis and treatment is usually by endoscopy and extraction and identification of the larvae. Allergic forms are usually diagnosed by prick-test and/or allergen-specific IgE detection and treated with a suitable anti-allergy treatment. The patient is also warned against further consumption of marine fish or squid, as these may be infected with Anisakis. The most common method of prevention is thermal treatment of the entire fish or squid prior to consumption (>60 °C, >1 min or - 20 °C, >24 h). Useful measures for the control of anisakiasis would be to establish a national register of cases, to initiate educational campaigns for the general public and consciousness-raising and training campaigns for health professionals. These would be complemented by control measures for the relevant sectors of the economy: fish operators, fish farming, fishermen, fishmongers, fish industry and catering facilities. Possible genetic predisposition for allergy to Anisakis and the possible relationship between anisakiasis and cancer would also require further investigation.

Occurrence of larval anisakids in horse mackerel (Trachurus trachurus) caught in Portuguese waters

The third-stage larvae (L3) of the Anisakidae family are parasitic nematodes with zoonotic impact and are frequently encountered in the organs and musculature of various fish intended for human consumption. Since Anisakis simplex (s.s.) and A. pegreffii are the major aetiological agents of human disease, this study aims to combine the morphological and molecular data on the recovered anisakid larvae to contribute to a simplified morphological distinction of those species and conducted a survey of anisakid larvae infection in horse mackerel (Trachurus trachurus). Here, 116 horse mackerel caught in Portuguese waters were analysed for the presence of L3 of anisakids, and 3148 larvae were collected, of which only 30% were retrieved during visual inspection. As such, visual inspection does not appear to be very effective in anisakid detection. A prevalence of 84.5% of infected fish was found, and the mean intensity and mean abundance were 32.1 and 27.1 parasites per fish, respectively. The morphological and molecular analyses of 196 L3 randomly chosen from the total sample of parasites demonstrated the presence of L3 of mostly Anisakis spp., with only one L3 of Hysterothylacium aduncum. Relative frequencies of 62.9% for A. pegreffii and 37.1% for A. simplex (s.s.) were obtained. The morphometry differences between these two sibling species were evaluated, and the results demonstrated significant differences between the length of the ventriculus and the length of the oesophagus. Precisely, A. simplex (s.s.) has a longer oesophagus and ventriculus than A. pegreffii. As such, these differences may be used to distinguish the two species through morphological analysis.

Advances in Omic Studies Drive Discoveries in the Biology of Anisakid Nematodes

Advancements in technologies employed in high-throughput next-generation sequencing (NGS) methods are supporting the spread of studies that, combined with advances in computational biology and bioinformatics, have greatly accelerated discoveries within basic and biomedical research for many parasitic diseases. Here, we review the most updated "omic" studies performed on anisakid nematodes, a family of marine parasites that are causative agents of the fish-borne zoonosis known as anisakiasis or anisakidosis. Few deposited data on Anisakis genomes are so far available, and this still hinders the deep and highly accurate characterization of biological aspects of interest, even as several transcriptomic and proteomic studies are becoming available. These have been aimed at discovering and characterizing molecules specific to peculiar developmental parasitic stages or tissues, as well as transcripts with pathogenic potential as toxins and allergens, with a broad relevance for a better understanding of host-pathogen relationships and for the development of reliable diagnostic tools.

Mass Spectrometry Based-Proteomic Analysis of Anisakis spp.: A Preliminary Study towards a New Diagnostic Tool

Anisakiasis is nowadays a well-known infection, mainly caused by the accidental ingestion of Anisakis larvae, following the consumption of raw or undercooked fishes and cephalopods. Due to the similarity of symptoms with those of common gastrointestinal disorders, this infection is often underestimated, and the need for new specific diagnostic tools is becoming crucial. Given the remarkable impact that MALDI–TOF MS biotyping had in the last decade in clinical routine practice for the recognition of bacterial and fungi strains, a similar scenario could be foreseen for the identification of parasites, such as nematodes. In this work, a MALDI–TOF MS profiling of Anisakis proteome was pursued with a view to constructing a first spectral library for the diagnosis of Anisakis infections. At the same time, a shotgun proteomics approach by LC–ESI–MS/MS was performed on the two main fractions obtained from protein extraction, to evaluate the protein species enriched by the protocol. A set of MALDI–TOF MS signals associated with proteins originating in the ribosomal fraction of the nematode extract was selected as a potential diagnostic tool for the identification of Anisakis spp.

Immunoreactive Proteins in the Esophageal Gland Cells of Anisakis Simplex Sensu Stricto Detected by MALDI-TOF/TOF Analysis

In plant and animal nematode parasites, proteins derived from esophageal gland cells have been shown to be important in the host-nematodes relationship but little is known about the allergenic potential of these proteins in the genus Anisakis. Taking into account the increase of anisakiasis and allergies related to these nematodes, immunoreactive properties of gland cell proteins were investigated. Two hundred ventricles were manually dissected from L3 stage larvae of Aniskakis simplex s.s. to allow direct protein analysis. Denaturing gel electrophoresis followed by monochromatic silver staining which revealed the presence of differential (enriched) proteins when compared to total nematode extracts. Such comparison was performed by means of 1D and 2D electrophoresis. Pooled antisera from Anisakis spp.-allergic patients were used in western blots revealing the presence of 13 immunoreactive bands in the ventricular extracts in 1D, with 82 spots revealed in 2D. The corresponding protein bands and spots were excised from the silver-stained gel and protein assignation was made by MALDI-TOF/TOF. A total of 13 (including proteoforms) were unambiguously identified. The majority of these proteins are known to be secreted by nematodes into the external environment, of which three are described as being major allergens in other organisms with different phylogenetic origin and one is an Anisakis simplex allergen.

Differences in Gene Expression Profiles of Seven Target Proteins in Third-Stage Larvae of Anisakis simplex (Sensu Stricto) by Sites of Infection in Blue Whiting (Micromesistius poutassou)

The third-stage larvae of the parasitic nematode genus Anisakis tend to encapsulate in different tissues including the musculature of fish. Host tissue penetration and degradation involve both mechanic processes and the production of proteins encoded by an array of genes. Investigating larval gene profiles during the fish infection has relevance in understanding biological traits in the parasite’s adaptive ability to cope with the fish hosts’ defense responses. The present study aimed to investigate the gene expression levels of some proteins in L3 of A. simplex (s.s.) infecting different tissues of blue whiting Micromesistius poutassou, a common fish host of the parasite in the NE Atlantic. The following genes encoding for Anisakis spp. proteins were studied: Kunitz-type trypsin inhibitor (TI), hemoglobin (hb), glycoprotein (GP), trehalase (treh), zinc metallopeptidase 13 (nas 13), ubiquitin-protein ligase (hyd) and sideroflexin 2 (sfxn 2). Significant differences in gene transcripts (by quantitative real-time PCR, qPCR) were observed in larvae located in various tissues of the fish host, with respect to the control. ANOVA analysis showed that relative gene expression levels of the seven target genes in the larvae are linked to the infection site in the fish host. Genes encoding some of the target proteins seem to be involved in the host tissue migration and survival of the parasite in the hostile target tissues of the fish host.

Comparative Transcriptomics Reveals Clues for Differences in Pathogenicity between Hysterothylacium aduncum, Anisakis simplex sensu stricto and Anisakis pegreffii

Ascaridoid nematodes are widespread in marine fishes. Despite their major socioeconomic importance, mechanisms associated to the fish-borne zoonotic disease anisakiasis are still obscure. RNA-Seq and de-novo assembly were herein applied to RNA extracted from larvae and dissected pharynx of Hysterothylacium aduncum (HA), a non-pathogenic nematode. Assembled transcripts in HA were annotated and compared to the transcriptomes of the zoonotic species Anisakis simplex sensu stricto (AS) and Anisakis pegreffii (AP). Approximately 60,000,000 single-end reads were generated for HA, AS and AP. Transcripts in HA encoded for 30,254 putative peptides while AS and AP encoded for 20,574 and 20,840 putative peptides, respectively. Differential gene expression analyses yielded 471, 612 and 526 transcripts up regulated in the pharynx of HA, AS and AP. The transcriptomes of larvae and pharynx of HA were enriched in transcripts encoding collagen, peptidases, ribosomal proteins and in heat-shock motifs. Transcripts encoding proteolytic enzymes, anesthetics, inhibitors of primary hemostasis and virulence factors, anticoagulants and immunomodulatory peptides were up-regulated in AS and AP pharynx. This study represents the first transcriptomic characterization of a marine parasitic nematode commonly recovered in fish and probably of negligible concern for public health.

De novo transcriptome sequencing and analysis of Anisakis pegreffii (Nematoda: Anisakidae) third-stage and fourth stage larvae

Anisakis pegreffii is known as one of the causes of a fish-borne zoonosis, anisakidosis. Despite its significant public health and food hygiene impacts, little is known of the pathogenesis, genetic background of this parasite, at least partly due to the lack of genome and transcriptome information. In this study, RNA-seq and de novo assembly were conducted to obtain transcriptome profiles of the A. pegreffii third and fourth larvae. The third stage larvae (APL3) were collected from chub mackerel and the fourth stage larvae (APL4) were obtained by in vitro culture. In total, 47,243 and 43,660 unigenes were expressed in APL3 and APL4 transcriptomes. Of them, 18,753 were known and 28,490 were novel for APL3, while 18,996 were known and 24,664 were novel for APL4. The most abundantly expressed genes in APL3 were mitochondrial enzymes (COI, COII, COIII) and polyubiquitins (UBB, UBIQP_XENLA). Collagen-related genes (col-145, col-34, col-138, Bm1_54705, col-40) were the most abundantly expressed in APL4. Mitochondrial enzyme genes (COIII, COI) were also highly expressed in APL4. Among the transcripts, 614 were up-regulated in APL3, while 1,309 were up-regulated in APL4. Several protease and protein biosynthesis-related genes were highly expressed in APL3, all of which are thought to be crucial for invading host tissues. Collagen synthesis-related genes were highly expressed in APL4, reflecting active biosynthesis of collagens occurs during moulting process of APL4. Of these differentially expressed genes, several genes (SI, nas-13, EF-TSMT, SFXN2, dhs-27) were validated to highly transcribed in APL3, while other genes (col-40, F09E10.7, pept-1, col-34, VIT) in APL4. The biological roles of these genes in vivo will be deciphered when the reference genome sequences are available, together with in vitro experiments.

Functional Ultrastructure of the Excretory Gland Cell in Zoonotic Anisakids (Anisakidae, Nematoda)

Excretory and secretory products are crucial for parasite infectivity and host immunomodulation, but the functioning and ultrastructure of the excretory gland cell (EC) that produces these products are still scarcely understood and described. In light of growing reports on anisakiasis cases in Europe, we aimed to characterise the EC of larval Anisakispegreffii and adult Pseudoterranovaazarasi. In the latter, EC starts 0.85 mm from the head tip, measuring 1.936 × 0.564 mm. Larval EC shows a long nucleus with thorn-like extravaginations toward the cytoplasm, numerous electron-dense and -lucent secretory granules spanning from the perinuclear to subplasmalemmal space, an elevated number of free ribosomes, small, spherical mitochondria with few cristae and a laminated matrix, small and few Golgi apparatuses, and few endoplasmic reticula, with wide cisternae complexes. Ultrastructure suggests that anaerobic glycolysis is the main metabolic pathway, obtained through nutrient endocytosis across the pseudocoelomic surface of the EC plasmalemma and its endocytic canaliculi. Thorn-like extravaginations of EC karyotheca likely mediate specific processes (Ca2+ signaling, gene expression, transport, nuclear lipid metabolism) into the extremely wide EC cytosol, enabling focal delivery of a signal to specific sites in a short time. These functional annotations of parasitic EC should help to clarify anisakiasis pathogenesis.

Genome-wide analysis of Anisakis simplex sensu lato: the role of carbohydrate metabolism genes in the parasite's development

Anisakis simplex sensu lato is a parasitic nematode which can cause gastric symptoms and/or allergic reactions in humans who consume raw and undercooked fish. Anisakiasis poses a growing health problem around the globe because it causes non-specific symptoms and is difficult to diagnose. This genome-wide study was undertaken to expand our knowledge of A. simplex s.l. at the molecular level and provide novel data for biological and biotechnological research into the analyzed species and related nematodes. A draft genome assembly of the L3 stage of A. simplex s.l. was analyzed in detail, and changes in the expression of carbohydrate metabolism genes during the parasite's life cycle were determined. To our knowledge, this is the first genome to be described for a parasitic nematode of the family Anisakidae to date. We identified genes involved in parasite-specific pathways, including carbohydrates metabolism, apoptosis and chemo signaling. A total of 7607 coding genes were predicted. The genome of A. simplex s.l. is highly similar to genomes of other parasitic nematodes. In particular, we described a valuable repository of genes encoding proteins of trehalose and glycogen metabolism, and we developed the most comprehensive data set relating to the conversion of both saccharides which play important roles during the parasite's life cycle in a host environment. We also confirmed that trehalose is synthesized at the expense of glycogen. Trehalose anabolism and glycogen catabolism were the predominant processes in stages L4 and L5, which could confirm our and other authors' previous reports that trehalose is synthesized at the expense of glycogen. The A. simplex s.l. genome provides essential data for post-genomic research into the biology of gastrointestinal and allergic anisakiasis in humans and the biology of other important parasitic helminths.

Gene expression profiles of antigenic proteins of third stage larvae of the zoonotic nematode Anisakis pegreffii in response to temperature conditions

Anisakis pegreffii, a recognised etiological agent of human anisakiasis, is a parasite of homeothermic hosts at the adult stage and of ectothermic hosts at the third larval stage. Among distinct factors, temperature appears to be crucial in affecting parasite hatching, moulting and to modulate parasite-host interaction. In the present study, we investigated the gene transcripts of proteins having an antigenic role among excretory secretory products (ESPs) (i.e., a Kunitz-type trypsin inhibitor, A.peg-1; a glycoprotein, A.peg-7; and the myoglobin, A.peg-13) after 24 h, in A. pegreffii larvae maintained in vitro, under controlled temperature conditions. Temperatures were 37 °C and 20 °C, resembling respectively homeothermic and ectothermic hosts conditions, and 7 °C, the cold stress condition post mortem of the fish host. Primers of genes coding for these ESPs to be used in quantitative real-time PCR were newly designed, and qRT-PCR conditions developed. Expression profiles of the genes A.peg-1 and A.peg-13 were significantly up-regulated at 20 °C and 37 °C, with respect to the control (larvae kept at 2 °C for 24 h). Conversely, transcript profiles of A.peg-7 did not significantly change among the chosen temperature conditions. In accordance with the observed transcript profiles, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed the presence of the three target ESPs at 37 °C, while only A.peg-13 was observed at 7 °C. The results suggest that temperature conditions do regulate the gene expression profiles of A.peg-1 and A.peg-13 in A. pegreffii larvae. However, regulation of the glycoprotein A.peg-7 is likely to be related to other factors such as the host's immune response.

Differential proteolytic activity in Anisakis simplex s.s. and Anisakis pegreffii, two sibling species from the complex Anisakis simplex s.l., major etiological agents of anisakiasis

Proteolytic activity was studied in two sibling species of Anisakis (Nematoda: Anisakidae), A. simplex s.s. and A. pegreffii, throughout their in vitro development from third larval stage (L3) from the host fish (L3-0h) to fourth larval stage (L4) obtained in culture. Proteases have a significant role in the lifecycle of the parasite and in the pathogen-host relationship. Proteolytic activity peaks were detected at pH 6.0 and 8.5. Protease activity was detected in all the developmental stages of the two species studied at both pH values. These pH values were used for assaying with specific inhibitors which permitted the determination of metalloprotease activity, and, to a lesser extent, that of serine and cysteine protease. Aspartic protease activity was only detected at pH 6.0. At this pH, L4 larvae showed higher proteolytic activity than L3 larvae in both species (p < 0.001), the majority of activity being due to metalloproteases and aspartic proteases, which could be related to nutrition, especially the latter, as occurs in invertebrates. At pH 8.5, proteolytic activity was higher in A. simplex s.s. than in A. pegreffii (p < 0.01). At this pH, the majority of activity was due to metalloproteases in all developmental phases of both species, although, in L3-0h, the activity of these proteases was significantly higher (p < 0.03) in A. simplex s.s. than in A. pegreffii. This could be related to the greater invasive capacity of the former. Serine proteases have frequently been implicated in the invasive capacity and pathogenicity of some parasites. This may be related to the significantly higher activity (p ≤ 0.05) of serine protease in all the larval stages of A. simplex studied at pH 6.0. Thus, there are interspecific differences in proteases that have been related to pathogenesis in nematodes. These differences could thus be contributing to the previously reported differences in pathogenicity between these two Anisakis species.

Induction of tolerogenic properties by Anisakis larval antigens on murine dendritic cells

AIMS

The objective of this work is to investigate whether Anisakis simplex larval antigens present immunomodulatory properties by the induction of tolerogenic dendritic cells (DCs) from two strains of mice (BALB/c and C57BL/6J).

METHODS AND RESULTS

We used mouse bone marrow-derived DCs. We determined their antigen-presenting ability by expression of membrane markers (MHC I and MHC II, CD80, CD86) and intracellular expression levels of IL-10 and IL-12 cytokines. We also analysed whether stimulation with A simplex larval antigens is enhanced by the co-administration of the TLR4 and TLR9 agonists [LPS _{E coli 026B6} and CpG (ODN1826), respectively]. Two differential types of responses were found in the two mouse strains studied: the BALB/c strain showed an acute and inflammatory response, whereas the C57BL/6J mice developed a more discrete and resistant response. This suggests the coexistence of two opposing responses generated by A simplex larval antigens and confirms that the host genetic basis plays a role in the development of a Th2 or T_reg response.

CONCLUSION

The study of the mechanisms by which Anisakis manipulates the immune response through anti-inflammatory molecules is of interest not only for the direct application on the development of anthelmintic strategies, but also for the development of new anti-inflammatory products.

Transcriptomic Resources for Parasitic Nematodes of Veterinary Importance

Parasitic nematodes are important pathogens of animals, causing diseases that impact on agricultural production worldwide. Research on these worms has been constrained by a lack of genetic and genomic tools. Nonetheless, over the past decade this field has made substantial advances, many of which have been led by transcriptomic sequencing. The present review summarises major transcriptomic studies of veterinary parasitic nematodes in recent years, and comments on overarching themes stemming from this work that inform our understanding of parasitism. Finally, we comment on current, state-of-the-art informatic tools for the analysis of complex worm transcriptomes to extract maximum the molecular information from them.

Molecular and Cellular Response to Experimental Anisakis pegreffii (Nematoda, Anisakidae) Third-Stage Larval Infection in Rats

Background: Anisakiasis is a zoonotic disease caused by accidental ingestion of live Anisakis spp. third-stage larvae present in raw or undercooked seafood. Symptoms of this emerging infectious disease include mild-to-severe abdominal pain, nausea, and diarrhea. Some patients experience significant allergic reactions. Aims: In order to better understand the onset of anisakiasis, we aimed to: (i) histopathologically describe severe inflammatory/hemorrhagic infection site lesions in Sprague-Dawley rats experimentally infected with Anisakis pegreffii larvae; and (ii) qualitatively and quantitatively characterize the transcriptomes of affected tissues using RNA-Seq. Methodology: The experiment was performed on 35 male rats, sacrificed at 5 time points (6, 10, 18, 24, and 32 h post-infection). Gastric intubation was performed with 10 A. pegreffii larvae (N = 5 infected rats per time point) or 1.5 ml of saline (external control N = 2 rats). 16 pools, seven for muscle tissues and nine for stomach tissues, were created to obtain robust samples for estimation of gene expression changes depicting common signatures of affected versus unaffected tissues. Illumina NextSeq 500 was used for paired-end sequencing, while edgeR was used for count data and differential expression analyses. Results: In total, there were 1372 (855 up and 517 down) differentially expressed (DE) genes in the Anisakis-infected rat stomach tissues, and 1633 (1230 up and 403 down) DE genes in the muscle tissues. Elicited strong local proinflammatory reaction seems to favor the activation of the interleukin 17 signaling pathway and the development of the T helper 17-type response. The number of DE ribosomal genes in the Anisakis-infected stomach tissue suggests that A. pegreffii larvae might induce ribosomal stress in the early infection stage. However, the downstream pathways and post-infection responses require further study. Histopathology revealed severe inflammatory/hemorrhagic lesions caused by Anisakis infection in the rat stomach and muscle tissues in the first 32 h. The lesion sites showed infiltration by polymorphonuclear leukocytes (predominantly neutrophils and occasional eosinophils), and to a lesser extent, macrophages. Conclusion: Understanding the cellular and molecular mechanisms underlying host responses to Anisakis infection is important to elucidate many aspects of the onset of anisakiasis, a disease of growing public health concern.

Functional insights into the infective larval stage of Anisakis simplex s.s., Anisakis pegreffii and their hybrids based on gene expression patterns

BACKGROUND

Anisakis simplex sensu stricto and Anisakis pegreffii are sibling species of nematodes parasitic on marine mammals. Zoonotic human infection with third stage infective larvae causes anisakiasis, a debilitating and potentially fatal disease. These 2 species show evidence of hybridisation in geographical areas where they are sympatric. How the species and their hybrids differ is still poorly understood.

RESULTS

Third stage larvae of Anisakis simplex s.s., Anisakis pegreffii and hybrids were sampled from Merluccius merluccius (Teleosti) hosts captured in waters of the FAO 27 geographical area. Specimens of each species and hybrids were distinguished with a diagnostic genetic marker (ITS). RNA was extracted from pools of 10 individuals of each taxon. Transcriptomes were generated using Illumina RNA-Seq, and assembled de novo. A joint assembly (here called merged transcriptome) of all 3 samples was also generated. The inferred transcript sets were functionally annotated and compared globally and also on subsets of secreted proteins and putative allergen families. While intermediary metabolism appeared to be typical for nematodes in the 3 evaluated taxa, their transcriptomes present strong levels of differential expression and enrichment, mainly of transcripts related to metabolic pathways and gene ontologies associated to energy metabolism and other pathways, with significant presence of excreted/secreted proteins, most of them allergens. The allergome of the 2 species and their hybrids has also been thoroughly studied; at least 74 different allergen families were identified in the transcriptomes.

CONCLUSIONS

A. simplex s.s., A. pegreffi and their hybrids differ in gene expression patterns in the L3 stage. Strong parent-of-origin effects were observed: A. pegreffi alleles dominate in the expression patterns of hybrids albeit the latter, and A. pegreffii also display significant differences indicating that hybrids are intermediate biological entities among their parental species, and thus of outstanding interest in the study of speciation in nematodes. Analyses of differential expression based on genes coding for secreted proteins suggests that co-infections presents different repertoires of released protein to the host environment. Both species and their hybrids, share more allergen genes than previously thought and are likely to induce overlapping disease responses.

Molecular Epidemiology of Anisakis and Anisakiasis: An Ecological and Evolutionary Road Map

This review addresses the biodiversity, biology, distribution, ecology, epidemiology, and consumer health significance of the so far known species of Anisakis, both in their natural hosts and in human accidental host populations, worldwide. These key aspects of the Anisakis species' biology are highlighted, since we consider them as main driving forces behind which most of the research in this field has been carried out over the past decade. From a public health perspective, the human disease caused by Anisakis species (anisakiasis) appears to be considerably underreported and underestimated in many countries or regions around the globe. Indeed, when considering the importance of marine fish species as part of the everyday diet in many coastal communities around the globe, there still exist significant knowledge gaps as to local epidemiological and ecological drivers of the transmission of Anisakis spp. to humans. We further identify some key knowledge gaps related to Anisakis species epidemiology in both natural and accidental hosts, to be filled in light of new 'omic' technologies yet to be fully developed. Moreover, we suggest that future Anisakis research takes a 'holistic' approach by integrating genetic, ecological, immunobiological, and environmental factors, thus allowing proper assessment of the epidemiology of Anisakis spp. in their natural hosts, in human populations, and in the marine ecosystem, in both space and time.