In vitro culture of the zoonotic nematode Anisakis pegreffii (Nematoda, Anisakidae)

Hybridization and introgression of the mitochondrial genome between the two species Anisakis pegreffii and A. simplex (s.s.) using a wide genotyping approach: evolutionary and ecological implications

Anisakis pegreffii and A. simplex (s.s.) are the two zoonotic anisakids infecting cetaceans as well as pelagic/demersal fish and squids. In European waters, A. pegreffii prevails in the Mediterranean Sea, while A. simplex (s.s.) in the NE Atlantic Ocean. Abiotic conditions likely play a significant role in shaping their geographical distribution. The Iberian Atlantic and Alboran Sea waters are sympatric areas of the two species. A total of 429 adults and L3 stage from both sympatric and allopatric areas were studied by a wide nuclear genotyping approach (including newly and previously found diagnostic single nucleotide polymorphisms (SNPs) at nuclear DNA (nDNA) and microsatellite DNA loci) and sequenced at mitochondrial DNA (mtDNA) cox2. Admixture between the two species was detected in the sympatric areas studied by STRUCTURE Bayesian analysis; NEWHYBRIDS revealed different categories of hybridization between the two species, representing approximately 5%. A tendency for F1 female hybrids to interbreed with the parental species at the geographical distribution limits of both species was observed. This finding suggests that hybridization occurs when the two parental species significantly differ in abundance. Mitochondrial introgression of A. simplex (s.s.) in A. pegreffii from Mediterranean waters was also detected, likely as a result of past and/or paleo-introgression events. The high level of genetic differentiation between the two species and their backcrosses indicates that, despite current hybridization, reproductive isolation which maintains evolutionary boundaries between the two species, exists. Possible causes of hybridization phenomena are attempted, as well as their evolutionary and ecological implications, also considering a sea warming scenario in European waters.

Anisakidae and Anisakidosis: A Public Health Perspective

Fish and seafood are increasingly recognised as safe and nutritiously valuable foods of animal origin, being a source of about 17% of animal protein globally. Novel culinary trends encourage the consumption of raw or thermally lightly processed fishery products. At the same time, consumers prefer wild, fresh and whole fish over farmed or processed fish. However, the consumption of raw or undercooked fish and other marine organisms poses a risk of contracting parasitic infections, potentially representing a public health risk. Among the most common seafoodborne parasites are members of the Anisakidae family, especially the genus Anisakis, which can cause potentially detrimental effects to human health. These parasites are the causative agent of a zoonosis termed anisakidosis that is prevalent in countries with high per capita fish consumption. Although the number of annual clinical cases varies among countries and regions and is generally not high, sensitisation to this parasite in the general population seems to be considerably higher. Therefore, anisakidosis is still significantly underreported and misdiagnosed globally, making it a disease of rising public health concerns. To prevent infection and mitigate potential negative effects on human health, proper preventive measures such as gutting the fish, freezing or thermal processing are needed. Moreover, a holistic approach implementing One Health principles together with educational campaigns towards the general public and primary care physicians can extend the knowledge on the occurrence of these parasites in their natural hosts and the diagnosis and incidence of anisakidosis, with a final goal to minimize risks for human health and reducing costs for health systems.

Diatoms-endoparasite association in fish from the marine pacific coast of Colombia (Buenaventura)

The association of parasites and diatoms has been previously reported as an important mechanism to control bacteria and parasites to avoid resistance to chemical usage. The aim of this study was to investigate the association between diatoms genus and parasites within the gastrointestinal compartments (GICs) of commercial fish in fisheries of the marine Pacific coast of Colombia (Buenaventura). A total of 104 GICs from marine fish were sampled. The GICs analysis revealed 14 diatom genera (N = 14). The most prevalent were Coscinodiscus spp., which was present in 58/104 samples, 55.8% [95% CI = 37.5-62.1%]; Cyclotella spp., 28/104, 26.9% [95% CI = 0-25%]; Paralia spp., 26/104, 25% [95% CI = 12.5-44.8%]; Gyrosigma spp., 11/104, 10.6% [95% CI = 0-33.3%]; Navicula spp., 11/104, 10.6%, [95% CI = 0-20.7%]. The GICs analysis revealed a diversity of genera parasites. The most prevalent were Ameboid cysts, 25/104, 24% [95% CI = 12.5-48.3%]; Eimeria spp., 11/104, 10.6% [95% CI = 10.3-15.7%]; Anisakis spp., 29/104, 27.1% [95% CI = 27.1 (SD±12.9%)]. This is the first report concerning diatoms and parasites association in fish from the Pacific Coast of Colombia and highlights the relevance of Coscinodiscus spp. and Gyrosigma spp. as important diatoms and potential candidates for studying pharmaceutical action in aquaculture. Further studies about diatoms-parasites association in aquaculture are required.

Anisakis extracellular vesicles elicit immunomodulatory and potentially tumorigenic outcomes on human intestinal organoids

BACKGROUND

Anisakis spp. are zoonotic nematodes causing mild to severe acute and chronic gastrointestinal infections. Chronic anisakiasis can lead to erosive mucosal ulcers, granulomas and inflammation, potential tumorigenic triggers. How Anisakis exerts its pathogenic potential through extracellular vesicles (EVs) and whether third-stage infective larvae may favor a tumorigenic microenvironment remain unclear.

METHODS

Here, we investigated the parasite's tumorigenic and immunomodulatory capabilities using comparative transcriptomics, qRT-PCR and protein analysis with multiplex ELISA on human intestinal organoids exposed to Anisakis EVs. Moreover, EVs were characterized in terms of shape, size and concentration using classic TEM, SEM and NTA analyses and advanced interferometric NTA.

RESULTS

Anisakis EVs showed classic shape features and a median average diameter of around 100 nm, according to NTA and iNTA. Moreover, a refractive index of 5-20% of non-water content suggested their effective biological cargo. After treatment of human intestinal organoids with Anisakis EVs, an overall parasitic strategy based on mitigation of the immune and inflammatory response was observed. Anisakis EVs impacted gene expression of main cytokines, cell cycle regulation and protein products. Seven key genes related to cell cycle regulation and apoptosis were differentially expressed in organoids exposed to EVs. In particular, the downregulation of EPHB2 and LEFTY1 and upregulation of NUPR1 genes known to be associated with colorectal cancer were observed, suggesting their involvement in tumorigenic microenvironment. A statistically significant reduction in specific mediators of inflammation and cell-cycle regulation from the polarized epithelium as IL-33R, CD40 and CEACAM1 from the apical chambers and IL-1B, GM-CSF, IL-15 and IL-23 from both chambers were observed.

CONCLUSIONS

The results here obtained unravel intestinal epithelium response to Anisakis EVs, impacting host's anthelminthic strategies and revealing for the first time to our knowledge the host-parasite interactions in the niche environment of an emerging accidental zoonosis. Use of an innovative EV characterization approach may also be useful for study of other helminth EVs, since the knowledge in this field is very limited.

An inside out journey: biogenesis, ultrastructure and proteomic characterisation of the ectoparasitic flatworm Sparicotyle chrysophrii extracellular vesicles

BACKGROUND

Helminth extracellular vesicles (EVs) are known to have a three-way communication function among parasitic helminths, their host and the host-associated microbiota. They are considered biological containers that may carry virulence factors, being therefore appealing as therapeutic and prophylactic target candidates. This study aims to describe and characterise EVs secreted by Sparicotyle chrysophrii (Polyopisthocotyla: Microcotylidae), a blood-feeding gill parasite of gilthead seabream (Sparus aurata), causing significant economic losses in Mediterranean aquaculture.

METHODS

To identify proteins involved in extracellular vesicle biogenesis, genomic datasets from S. chrysophrii were mined in silico using known protein sequences from Clonorchis spp., Echinococcus spp., Fasciola spp., Fasciolopsis spp., Opisthorchis spp., Paragonimus spp. and Schistosoma spp. The location and ultrastructure of EVs were visualised by transmission electron microscopy after fixing adult S. chrysophrii specimens by high-pressure freezing and freeze substitution. EVs were isolated and purified from adult S. chrysophrii (n = 200) using a newly developed ultracentrifugation-size-exclusion chromatography protocol for Polyopisthocotyla, and EVs were characterised via nanoparticle tracking analysis and tandem mass spectrometry.

RESULTS

Fifty-nine proteins involved in EV biogenesis were identified in S. chrysophrii, and EVs compatible with ectosomes were observed in the syncytial layer of the haptoral region lining the clamps. The isolated and purified nanoparticles had a mean size of 251.8 nm and yielded 1.71 × 108 particles · mL-1. The protein composition analysis identified proteins related to peptide hydrolases, GTPases, EF-hand domain proteins, aerobic energy metabolism, anticoagulant/lipid-binding, haem detoxification, iron transport, EV biogenesis-related, vesicle-trafficking and other cytoskeletal-related proteins. Several identified proteins, such as leucyl and alanyl aminopeptidases, calpain, ferritin, dynein light chain, 14-3-3, heat shock protein 70, annexin, tubulin, glutathione S-transferase, superoxide dismutase, enolase and fructose-bisphosphate aldolase, have already been proposed as target candidates for therapeutic or prophylactic purposes.

CONCLUSIONS

We have unambiguously demonstrated for the first time to our knowledge the secretion of EVs by an ectoparasitic flatworm, inferring their biogenesis machinery at a genomic and transcriptomic level, and by identifying their location and protein composition. The identification of multiple therapeutic targets among EVs' protein repertoire provides opportunities for target-based drug discovery and vaccine development for the first time in Polyopisthocotyla (sensu Monogenea), and in a fish-ectoparasite model.

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.

A novel rhabdovirus detected in Anisakis larvae distributed in the coastal areas of Japan: Viral genome analysis and possible coevolutionary relationship between virus and host nematodes

In the last decade, it has become evident that various RNA viruses infect helminths including Order Ascaridida. However, there is still no information available for viruses infecting Anisakis. We herewith demonstrate the presence of a novel rhabdovirus from Anisakis larvae detected by next-generation sequencing analysis and following RT-PCR. We determined the nearly all nucleotide sequence (12,376 nucleotides) of the viral genome composed of seven open reading frames, and we designated the virus as Suzukana rhabdo-like virus (SkRV). BLASTx search indicated that SkRV is a novel virus belonging to the subfamily Betanemrhavirus, rhabdovirus infecting parasitic nematodes of the Order Ascaridida. SkRV sequence was detectable only in the total RNA but not in the genomic DNA of Anisakis, ruling out the possibility of SkRV being an endogenous viral element incorporated into the host genomic DNA. When we individually tested Anisakis larvae obtained from Scomber japonicus migrating in the coastal waters of Japan, not all but around 40% were SkRV-positive. In the phylogenetic trees of Betanemrhavirus and of the host Ascaridida nematodes, we observed that evolutional distances of viruses were, to some extent, parallel with that of host nematodes, suggesting that viral evolution could have been correlated with evolution of the host. Although biological significance of SkRV on Anisakis larvae is still remained unknown, it is interesting if SkRV were somehow related to the pathogenesis of anisakiasis, because it is important matter of public health in Japan and European countries consuming raw marine fishes.

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.