Sensitive Detection and Quantification of Anisakid Parasite Residues in Food Products

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.

Anisakis spp, DNA detection in paraffin-embedded tissue biopsies recovered from patients with gastritis using real-time PCR in Bushehr, Persian Gulf, Iran

Anisakiasis is a zoonotic fish-born parasitic disease caused by anisakid nematodes. Paraffin-embedded blocks containing biopsy samples taken from patients suffering gastritis with unknown causes were investigated by real-time PCR, in the Bushehr region, Iran; where human anisakiasis has not been reported, so far. A total of 50 paraffin-embedded blocks were randomly selected from 250 archived blocks of the patients with gastritis. A SYBER green-based real-time PCR targeting the ITS1 region was developed for the identification of Anisakis genus. An 86 bp partial fragment of the Anisakis spp. ITS1 gene was amplified successfully. A total of 3 out of 50 samples (6 %) had positive amplification in the samples and their pathology reports showed a significant finding of moderate chronic gastritis with or without ulcers. In conclusion, the developed qPCR could be used for detecting Anisakis spp. larval DNA in human biopsy blocks. This study showed the hidden human cases of anisakiasis in the Bushehr for the first time.

Estimation of the number of Anisakis larvae in commercial fish using a descriptive model based on real-time PCR

BACKGROUND

Seafood parasitation by Anisakis (Anisakidae) larvae has been reported in most of the oceans and seas worldwide. The presence of these nematodes in commonly consumed fish represents a potential hazard for consumers as they can provoke gastrointestinal symptoms and allergic reactions. In the present work, the capacity of a SYBR Green qPCR protocol to quantify Anisakis larvae in commercial fish was evaluated using experimentally spiked samples with different numbers (0-50) of A. simplex third-stage larvae (L3). To verify the agreement of the obtained results, 25 naturally infected fish specimens of Atlantic blue whiting underwent a parallel visual inspection.

RESULTS

The logarithmic behavior of the Cq data obtained from the experimentally spiked samples allowed the development of a descriptive mathematical model that correlates the Cq value with the number of Anisakis larvae (R² = 0.9908, CV = 2.37%). In the commercial blue whiting specimens there was a high correlation between the results of the molecular technique and the visual inspection (R² = 0.9912); the Bland-Altman analysis showed that 94% of the differences were within the limits of agreement (-4.98 and 6.68), indicating the reliability of the descriptive mathematical model based on the SYBR Green qPCR technique.

CONCLUSION

The descriptive function presented based on the SYBR Green qPCR assay is promising as a sensitive and accurate tool for measuring the Anisakis larval load in commercial fish, with a potential application not only in the food industry but also in prevention programs for public health. © 2020 Society of Chemical Industry.

Development and Application of Novel Chemiluminescence Immunoassays for Highly Sensitive Detection of Anisakis simplex Proteins in Thermally Processed Seafood

The third-stage larvae (L3) of Anisakis simplex are the most important source of hidden allergens in seafood products. However, there exist no commercial methods for detecting Anisakis proteins in food. Furthermore, only a few methods have been validated for the detection of A. simplex in thermally processed food. The aims of our study are (i) the development and validation of high-sensitivity chemiluminescent (CL) immunoassays for the detection of A. simplex proteins in processed seafood, (ii) and A. simplex antigen detection in common seafood products from Polish markets. We developed and validated CL sandwich ELISA (S-ELISA) and CL competitive ELISA (C-ELISA) methods for A. simplex proteins detection in food, with respective detection limits of 0.5 and 5 ng/mL. The usefulness of the assays for detecting A. simplex proteins in highly processed food was evaluated by examination of autoclaved canned fish spiked with A. simplex larvae (1–8 larvae/200 g). Commercial real-time PCR was unable to detect A. simplex in autoclaved samples at all levels of enrichment with Anisakis larvae. CL-S-ELISA was used to test various types of seafood products from Polish markets. Among all tested products (n = 259), 28% were positive. A. simplex antigens were found mostly (n = 39) in smoked fish products: mackerel, herring, cod, and hake. Other positive samples were found in marinated herrings, canned cod livers, canned mackerels, and surimi sticks. In tuna, Atlantic argentine, anchovy, sardine, sprat, and squid products, A. simplex antigens were not detected. This study provides novel effective tools for the detection of A. simplex proteins in processed food and highlights the potential allergic hazards for Anisakis-sensitized Polish consumers of seafood.

A Critical Appraisal of Global Testing Protocols for Zoonotic Parasites in Imported Seafood Applied to Seafood Safety in Australia

It is not suggested that any country is intentionally exporting seafood which does not comply with Codex seafood-safety guidelines/codes/standards. However, with an open access resource such as fisheries, there is vast potential for errors to occur along convoluted supply chains, spanning multiple countries, which may negatively impact the safety of edible seafood products imported into Australia. Australian importation policy and inspection procedures are founded upon a bedrock of trust in the integrity, reliability and safety of the global seafood supply chain. In order for seafood imported to Australia to be considered safe the non-mandatory international health standards, governed by Codex Alimentarius, for seafood must be predicated upon the most efficacious methods and stringently governed by each exporting provenance. Currently, tests for zoonotic parasites are not applied to imported edible seafood products on arrival into Australia. Therefore, this critical analysis is aimed at discussing the effectiveness of current testing protocols for zoonotic parasites in edible seafood advised by Codex Alimentarius which may impact the safety of the product imported into Australia.

Validation of a Commercial Loop-Mediated Isothermal Amplification (LAMP) Assay for the Rapid Detection of Anisakis spp. DNA in Processed Fish Products

Parasites belonging to the Anisakis genera are organisms of interest for human health because they are responsible for the Anisakiasis zoonosis, caused by the ingestion of raw or undercooked fish. Furthermore, several authors have reported this parasite to be a relevant inducer of acute or chronic allergic diseases. In this work, a rapid commercial system based on Loop-Mediated Isothermal Amplification (LAMP) was optimised and validated for the sensitive and rapid detection of Anisakis spp. DNA in processed fish products. The specificity and sensitivity of the LAMP assay for processed fish samples experimentally infected with Anisakis spp. larvae and DNA were determined. The LAMP system proposed in this study was able to give positive amplification for all the processed fish samples artificially contaminated with Anisakis spp., giving sensitivity values equal to 100%. Specificity tests provided no amplification for the Contracaecum, Pseudoterranova, or Hysterothylacium genera and uninfected samples. The limit of detection (LOD) of the LAMP assay proposed was 102 times lower than the real-time PCR method compared. To the best of our knowledge, this is the first report regarding the application of the LAMP assay for the detection of Anisakis spp. in processed fish products. The results obtained indicate that the LAMP assay validated in this work could be a reliable, easy-to-use, and convenient tool for the rapid detection of Anisakis DNA in fish product inspection.

Prevalence of anisakid parasites in fish collected from Apulia region (Italy) and quantification of nematode larvae in flesh

Anisakis spp. and Hysterothylacium spp. are nematodes that commonly parasitize several fish species. Nematode larvae can be recovered in coelomic cavity and viscera, but also in flesh and have an important economic and public health impact. A total of 1144 subjects of wild teleosts, 340 samples of cephalopods and 128 specimens of farmed fish collected from Apulia region were analysed for anisakid larvae detection by visual inspection of coelomic cavity and viscera and by digestion of the flesh. No nematode larvae were found in farmed fish and cephalopod molluscs. All examined wild-caught fish species were parasitized, except for 5 species for each of which only a few subjects belonging to the same batch were sampled, therefore the results are just indicative. A total of 6153 larvae were isolated; among these, 271 larvae were found in the muscular portion. Larvae were identified by morphological method as belonging to the genera Anisakis (97.2%) (type I and type II) and Hysterothylacium (2.8%). Both nematodes could be found in all fish species, except for round sardinella (Sardinella aurita), infected only by Hysterothylacium spp. and for Mediterranean scaldfish (Arnoglossus laterna), little tunny (Euthynnus alleteratus) and chub mackerel (Scomber japonicus) infected only with Anisakis spp.. A sample of 185 larvae was sent to the National Reference Centre for Anisakiasis (C.Re.N.A.) of Sicily for identification at the species level: 180 larvae belonged to the species A. pegreffii and 2 larvae to A. physeteris. The remaining 3 larvae were identified at genus level as Hysterothylacium. Statistical indices such as prevalence, mean intensity and mean abundance were calculated. Chub mackerel (S. japonicus) was the species with the highest prevalence and mean intensity. Moreover, the average and the median values of larvae per 100 g of edible part for each fish species were determined to estimate the consumer exposure to Anisakis spp.. The obtained values were then recalculated by referring to the edible part of all specimens (infected and non-infected) forming a single parasitized batch, getting more realistic and objective data useful for risk assessment. Our results indicate that the consumption of raw or undercooked wild fish caught off Apulian coasts could result in the acquisition of anisakiasis; on the contrary, farmed fish and cephalopods appear to be safer for the consumer.

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.

Validation of a commercial kit aimed to the detection of pathogenic anisakid nematodes in fish products

Anisakids are parasitic nematodes responsible for a zoonosis that occurs following the ingestion of fish and fish products infected with larvae belonging to the genera Anisakis and Pseudoterranova. Rarely Contracaecum is found in association with gastric/intestinal illness, while Hysterothylacium is commonly considered not pathogenic. Although Real Time PCR assays have been recently used with the aim to detect and quantify these parasites in food products, methods applied did not undergo through extensive validation process, a feature highly desirable or mandatory in the case of testing laboratories accredited for the ISO EN 17025:2005. Here, a comprehensive study has been performed to validate a commercial kit based on multiplex real time PCR for the qualitative detection of Anisakis and Pseudoterranova. Inclusivity/exclusivity trials were carried out on DNA from species of the genera Anisakis, Pseudoterranova, Contracaecum, Hysterothylacium and Ascaris, on fish intentionally contaminated with Anisakis spp. and Pseudoterranova spp. and on marine organisms as fish, crustacean and squid to test the commercial kit on a large sample. The assay gave positive amplification for several Anisakis and Pseudoterranova species, while providing no signal for the members of the remaining genera. Each sample was correctly assigned either to Anisakis or Pseudoterranova, thus indicating that no cross-reaction occurred. The LOD was determined using two independent standard curves. Robustness was assayed by using two different thermocyclers in three distinct laboratories with different operators. The establishment of a validation dossier will permit the use of the commercial kit for the detection of Anisakis and Pseudoterranova DNA in fish and fish products intended for human consumption by public or private laboratories, following the requirements regarding the quality assurance processes described in the ISO EN 17025:2005.

A review of methods for nematode identification

Nematodes are non-segmented roundworms found in soil, aquatic environment, plants, or animals. Either useful or pathogenic, they greatly influence environmental equilibrium, human and animal health, as well as plant production. Knowledge on their taxonomy and biology are key issues to answer the different challenges associated to these organisms. Nowadays, most of the nematode taxonomy remains unknown or unclear. Several approaches are available for parasite identification, from the traditional morphology-based techniques to the sophisticated high-throughput sequencing technologies. All these techniques have advantages or drawbacks depending on the sample origin and the number of nematodes to be processed. This review proposes an overview of all newly available methods available to identify known and/or unknown nematodes with a specific focus on emerging high-throughput molecular techniques.

Putative hybrids between two Anisakis cryptic species: molecular genotyping using High Resolution Melting

The genus Anisakis includes nine recognized species and the complex of cryptic species Anisakis simplex s. l. is often associated with the human disease known as anisakiasis. During the last decades the use of nuclear ribosomal ITS allowed the identification and description of numerous anisakid nematodes and the discovery of recombinant genotypes or putative hybrids even in other parasitic helminths, such as those between A. simplex sensu stricto and A. pegreffii. The existence of pure hybrids of the two sibling species has been long debated due to the large recovery of larval forms from sympatric areas and the rare observation of adult hybrids. The aims of the present report were to identify anisakid nematodes collected from Stenella coeruleoalba using PCR-RFLP of ITS and to focus the interest on hybrid forms using a High Resolution Melting (HRM) and direct sequencing analyses, since the new record of putative hybrid at adult stage. The PCR-RFLP analysis enabled to identify A. simplex s.s., A. pegreffii, the heterozygous genotype of the two species and A. physeteris. The use of the genotyping approach based on HRM confirmed the profiles of the two species A. simplex s.s. and A. pegreffii, and of the hybrid individuals. The new record of adult hybrids in definitive hosts rekindles the long debate about their existence and their evolutionary meaning. Since the reproductive isolation between A. simplex s.s. and A. pegreffii is the assumption for their existence as separated species, the use of alternative molecular markers and population genetic studies on adult anisakids are recommended.

Foodborne anisakiasis and allergy

Human anisakiasis, a disease caused by Anisakis spp. (Nematoda), is often associated with clinical signs that are similar to those associated with bacterial or viral gastroenteritis. With the globalisation of the seafood industry, the risk of humans acquiring anisakiasis in developed countries appears to be underestimated. The importance of this disease is not only in its initial manifestation, which can often become chronic if the immune response does not eliminate the worm, but, importantly, in its subsequent sensitisation of the human patient. This sensitisation to Anisakis-derived allergens can put the patient at risk of an allergic exacerbation upon secondary exposure. This article reviews some aspects of this food-borne disease and explains its link to chronic, allergic conditions in humans.

Anisakis pegreffii: a quantitative fluorescence PCR assay for detection in situ

To facilitate improved diagnosis and detection of the third stage larva (L3) of Anisakis pegreffii from the Minnan-Taiwan bank fishing ground in Taiwan Strait, a real-time PCR method for the detection in situ and differentiation was developed to amplify a region of the second internal transcribed spacer (ITS-2) of this parasite. The real-time PCR assay was capable of detecting 1/3 of a single L3 in 30 mg of marine fish tissue, and also exhibited a high level of specificity for A. pegreffii, no fluorescence signals were observed in other five major larval anisakid species found in commercial marine fishes caught in this fishing ground.