New and known zoonotic nematode larvae within selected fish species from Queensland waters in Australia

Prevalence and molecular characterization of Hysterothylacium species infecting Pandora (Pagellus erythrinus) in the Mediterranean Sea of Egypt

Species of the genus Hysterothylacium are aquatic roundworms (nematodes) belonging to the family Raphidascarididae. Some species in this family are known to be associated with zoonotic diseases in humans after they consume their parasitic larvae in raw or undercooked fish. The aim of this research was to report the prevalence, morphology, and molecular characteristics of Hysterothylacium species in Pagellus erythrinus. A total of Two hundred fish were purchased from the fish market in Damanhour, Beheira Province, between December 2021 and November 2022 and subjected to examination. For molecular characterization, the internal transcribed spacer (ITS) region of nuclear ribosomal DNA and the mitochondrial cytochrome oxidase subunit 2 (COX-2) gene were used. Hysterothylacium species were morphologically described and identified from the intestine of Pagellus erythrinus in Beheira Province, Egypt. The PCR amplified 1087 bp and 629 bp of the target sequences of the ITS region and COX-2 gene, respectively. Sequence analysis revealed the Hysterothylacium thalassini species. The identified species provided novel biological data for the Hysterothylacium nematode in Pagellus erythrinus. The prevalence of Hysterothylacium species recovered from the intestine was 55%. The highest prevalence of 72% has been reported in summer compared to the lowest prevalence of 38% in the winter. Females had a higher prevalence of 61.8% than males, with 44.2%. The first detection, prevalence, and molecular characterization of H. thalassini in Pagellus erythrinus from Beheira Province, Egypt, was presented in this study.

Multidisciplinary approach to the diagnosis of Contracaecum magnipapillatum infections in Australian black noddies, Anous minutus (Charadriiformes: Laridae)

We provide the incidental necropsy findings associated with anisakid nematode infections of black noddy terns, Anous minutus Boie, 1844 (Charadriiformes: Laridae), from offshore islands in the southern Great Barrier Reef, Queensland, Australia. Specimens collected from the proventriculi were identified morphologically as Contracaecum magnipapillatum Chapin, 1925 (Rhabditida: Anisakidae), using light and scanning electron microscopy (SEM). The entire nuclear ribosomal DNA internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2) was amplified by polymerase chain reaction (PCR) and sequenced to provide reference sequences for morphologically well-identified voucher specimens. Interestingly, after an alignment with closely related taxa using BLAST, sequences of the ITS1 and ITS2 were 100% identical to the sequences assigned to Contracaecum septentrionale Kreis, 1955, from a razorbill, Alca torda Linnaeus, 1758 (Charadriiformes: Alcidae), from Spain. These results either raise questions about the ITS as a genetic marker for some members of Contracaecum, or the identity of the specimens assigned to C. septentrionale, given that no supporting morphological data was associated with them. We highlight the need for a combined morphological and molecular approach to parasite diagnostics and the use of multiple genetic loci to resolve the molecular taxonomy of cryptic species. Morphological identifications should be taxonomically robust, transparent and precede the deposition of molecular barcodes in public repositories. The gross and histopathological findings of our investigation concur with previous reports of widespread Contracaecum infections in black noddies and support the contention that Contracaecum spp. are an unlikely primary cause of mortality.

First record of Pseudoterranova decipiens in sprat (Sprattus sprattus) from the Baltic Sea

A dispersion of Anisakidae nematodes (particularly Contracaecum osculatum) among marine organisms in the Baltic Sea has been reported over the last decade. This is in line with an increase in the number of grey seal that act as final host for Contracaecum osculatum and Pseudoterranova sp., and are thus indispensable for the completion of their life cycles. Most attention has been paid to zoonotic nematode species, like Pseudoterranova sp., which have been noted in commercially important fish in the area. Little is known about the spread and transmission of Pseudoterranova sp. in the Baltic Sea. The aim of this study was to investigate whether sprat may play a role as a transport host for this Anisakidae. Samples were collected in three areas of the southern Baltic Sea (south and east of Bornholm, Słupsk Farrow and the Gulf of Gdańsk) during a research cruise in August 2019. A visual inspection of the viscera of 556 sprats was conducted. Parasites were identified using anatomomorphological and molecular methods. Nematodes were recorded only in sprat caught southeast of Bornholm (prevalence 2.7%; intensity of infection 1-4; abundance 0.05). Molecular identification revealed the presence of Pseudoterranova decipiens. This is the first report of P. decipiens in sprat from the Baltic Sea. Sprat is likely a transmitter of P. decipiens in the Baltic Sea food web.

Morphological and molecular characterization of Hysterothylacium larval morphotypes (Nematoda: Raphidascarididae) infecting edible marine fish in the Black Sea

The morphological and molecular identification of Hysterothylacium larval morphotypes in the Black Sea remains unresolved and incomplete. The aim of current study was to provide a detailed morphological identification with rDNA whole ITS (ITS‒1, 5.8S subunit, ITS‒2) and mtDNA cox2 sequences data of Hysterothylacium larval morphotypes infecting four commonly edible marine fish species, including European anchovy, Engraulis encrasicolus (L.), horse mackerel, Trachurus trachurus (L.), whiting, Merlangius merlangus (L.), and red mullet, Mullus barbatus ponticus (E.) in the Black Sea (FAO fishing area 37.4.2). Hysterothylacium larval morphotypes were morphologically classified, followed by whole ITS and cox2 sequencing. Four Hysterothylacium larval morphotypes, III, IV, VIII, and IX, are described based on morphological and molecular data. The present study provides the first study reporting whole ITS and cox2 sequences for Hysterothylacium larval morphotypes III, IV, VIII and III, IV, VIII, IX, respectively, in the Black Sea. Here, we offer a foundation for future research on the distribution, morphologic and molecular identification of Hysterothylacium larval morphotypes infecting edible some marine fish in the Black Sea.

Morphological and molecular characterization of Hysterothylacium spp. parasitizing Pomatomus saltatrix and Pagrus pagrus of the State of São Paulo, Brazil

Raphidascarid nematodes have been the focus of several studies, mainly due to the zoonotic potential of some species, even though the cases are underreported. Due to the difficulty in identifying their larvae, the use of diagnostic techniques involving morphological and molecular analyses has grown in the last 20 years. The present study had as objective the morphological and molecular characterization of the L3 larval types of Hysterothylacium collected in Pomatomus saltatrix and Pagrus pagrus from the Brazilian coast, close to the municipality of Santos, State of São Paulo. Twenty specimens of P. saltatrix were necropsied and Hysterothylacium type V (n = 257) and Hysterothylacium type X (n = 5) larvae were found. Five specimens of P. pagrus were necropsied and all were parasitized by Hysterothylacium type V larvae. The analyses showed a genetic proximity relationship between Hysterothylacium types V with other Hysterothylacium V and with H. deardorffoverstreetorum, although this is a species inquirenda. Haplotypes for Hysterothylacium type X found in the present study formed a monophyletic group with other Hysterothylacium X, H. amoyense, and H. zhoushanense. Through this study, new hosts and localities were registered for Hysterothylacium type V and Hysterothylacium type X.

Advancing understanding of the taxonomy and diversity of the genus Contracaecum in the great white pelican (Pelecanus onocrotalus)

Despite the wide distribution and health importance of anisakids of the genus Contracaecum, epidemiological data on their occurrence in definitive bird hosts are scarce, particularly from certain parts of the world that represent important wintering sites or migration stopovers for different bird species. In the present study, Contracaecum spp. infecting six great white pelicans (Pelecanus onocrotalus) in Israel were identified using light and scanning electron microscopy and phylogenetic analyses of nuclear internal transcribed spacer (ITS) and mitochondrial cytochrome c oxidase II (cox2). A PCR-RFLP method was also developed and applied to screen large numbers of Contracaecum parasites. Most (415/455) worms recovered were C. micropapillatum, followed by C. gibsoni (31/455), C. quadripapillatum (8/455), and C. multipapillatum E (1/455). Contracaecum micropapillatum from Israel and C. bancrofti from Australia are distinguishable by cox2 but less well resolved with ITS sequences, and could not be distinguished morphologically. Worms with cox2 matching C. gibsoni had ITS matching specimens identified as C. multipapillatum A. To the authors' knowledge, this represents the first of such studies in Israel and provides useful data on the ecology and distribution of different Contracaecum species of health and economic interest.

Ascaridoid nematodes infecting commercially important marine fish and squid species from Bangladesh waters in the Bay of Bengal

Parasitic ascaridoid nematodes occur in a wide range of marine organisms across the globe. Some species of the anisakid family (Ascaridoidea: Anisakidae) can cause gastrointestinal disease in humans (i. e. anisakidosis). Despite their importance as potentially hazardous parasites, the occurrence and infection characteristics of ascaridoids are still poorly known from many host species and geographical areas. This study investigated the diversity and infection levels of ascaridoid parasites in various commercial fish and squid host species off Bangladesh. Fish and squid specimens were visually inspected for nematodes using the UV-press method. Nematodes were assigned to genus level based on morphology and identified by sequence analyses of the entire ITS region and partial 28S rDNA and mtDNA cox2 genes. Third-stage larvae (L3) of Anisakis typica occurred at low prevalence (P = 10% and 8%, respectively) in the viscera of Selar crumenophthalmus and Trichiurus lepturus, while Hysterothylacium amoyense occurred in the viscera of Sardinella fimbriata (P = 1%) and the viscera and muscle of Harpadon nehereus (P = 32%) and T. lepturus (P = 76%). Lappetascaris sp. Type A L3 occurred in the mantle of the squid Uroteuthis duvaucelii (P = 11%). Anisakis and Lappetascaris species, and H. amoyense were firstly identified in the Bay of Bengal. The potentially zoonotic A. typica was only found in fish viscera. Hysterothylacium amoyense and Lappetascaris sp., both generally regarded as non-zoonotic, occurred at low prevalence in the muscle or mantle of fish or squid, respectively. Since consumption of raw or lightly processed seafood seems to be rare in Bangladesh, the risk of acquiring anisakidosis from consuming fishery products from off Bangladesh appears to be low. Due to its reddish appearance, the visual presence of H. amoyense larvae in fish flesh may represent a food quality issue.

Phylum Nematoda: trends in species descriptions, the documentation of diversity, systematics, and the species concept

This paper summarizes the trends in nematode species description and systematics emerging from a comparison of the latest comprehensive classification and census of Phylum Nematoda (Hodda 2022a, b) with earlier classifications (listed in Hodda 2007).   It also offers some general observations on trends in nematode systematics emerging from the review of the voluminous literature used to produce the classification.   The trends in nematodes can be compared with developments in the systematics of other organisms to shed light on many of the general issues confronting systematists now and into the future.  

Metazoan endoparasite fauna and feeding ecology of commercial fishes from Java, Indonesia

Despite being an important component of the marine ecosystem and posing health risks to human seafood consumers, fish parasites in Indonesia have yet to be adequately described. Here, we analyzed the diet and metazoan parasite fauna of seven commercial fish species (Alectis indica, Carangoides chrysophrys, Johnius borneensis, Mene maculata, Trichiurus lepturus, Upeneus asymmetricus, U. moluccensis) landed in Java, Indonesia. We isolated 11 endoparasite species, established 22 new host and 14 new locality records, and extended parasitological records of A. indica by 24%, C. chrysophrys by 25%, J. borneensis by 40%, M. maculata by 44%, U. asymmetricus by 100%, and U. moluccensis by 17%. We genetically identified the trematode Stephanostomum cf. uku (of Bray et al. 2005) from Alecta indica for the first time in Indonesia and provided the sequence of its 28S marker. Stomach content analysis revealed seven different prey items, and the examined fish species were grouped into four feeding categories, which differed significantly in their respective endoparasite fauna. All but two examined fish species hosted potentially zoonotic nematodes, which reveal a risk for parasite-borne diseases in Indonesian food fishes and call for more consequent monitoring with regard to seafood safety in this region. With this study, we were able to establish an association between the feeding ecology and the endoparasite fauna of marine fishes which will help to better understand the transmission pathways of (potentially zoonotic) parasites in food fishes in tropical waters.

In situ evidence of the role of Crangon crangon in infection of cod Gadus morhua with nematode parasite Hysterothylacium aduncum in the Baltic Sea

Cod was one of the most important fish species in the Baltic Sea, but its condition is deteriorating for several reasons, including an increasing parasite burden. The aim of this study was to determine the source of infection of Baltic cod with parasites by examination of invertebrates found in situ in the cod stomach. A total of 1681 cod were sampled during four research cruises in the southern Baltic Sea in 2012, 2013 and 2014 and the composition of their diet was analysed. Each prey item from cod stomach was identified to the lowest possible taxonomic level and a parasitological analysis of all invertebrates collected was performed. Crangon crangon, Saduria entomon and Mysis mixta were the most commonly represented invertebrates among food items. Hysterothylacium aduncum was found only in C. crangon. This host–parasite system is reported here for the first time in situ in the stomach of cod from the Baltic Sea, confirming the role of C. crangon in cod infection with H. aduncum.

The occurrence of Anisakis spp. in Australian waters: past, present, and future trends

As one of the world's megadiverse countries, Australian biodiversity is vital for global biodiversity. Nematodes belonging to the genus Anisakis (family Anisakidae) are an important part of this biodiversity due to their ability to be repeatedly transmitted among their intermediate hosts before reaching the top of the food pyramid. Therefore, they have a significant impact on the community structures of various ecosystems. In addition, globally, they are known to be of medical and veterinary significance. The aim of this article is to provide an update on the current knowledge about these important parasites in Australia. Since 1916, a total of 234 records of Anisakis spp. from various hosts and localities have been found in Australia. It is estimated that the occurrence of Anisakis spp. and their health impacts in at least 84, 98.5, and 95% of Australian marine mammals, fish, and water birds, respectively, have not been documented yet. The results of this study suggest Australia is perhaps home to the most diverse Anisakis fauna. Available information is dominated by reports of these parasites in fish hosts, many of them among edible fish. Given the popularity of seafood in Australia and the occurrence of infectious stages of Anisakis spp. in edible fish, all stakeholders should be made aware of the occurrence, prevalence, and survival of Anisakis spp. in seafood. Also, as more pet owners feed their pets with a variety of fish and seafood products, it is important for veterinarians to be aware of seafood transmitted Anisakis spp. in pet animals. This study also highlights several important knowledge gaps: (i) The detailed life cycle of Anisakis spp. in Australia is not known. Detecting their first intermediate hosts is important for better management of crustacean zooplankton populations in our waters. (ii) Research on Anisakis spp. in Australia has been restricted to limited taxonomical studies and should extend to other aspects of these important parasites. (iii) The capacity to identify parasite taxa to species is especially important for resolving biological diversity around Australia; however, opportunities to formally train in parasite taxonomy are rare and diminishing. There is a need to train researchers with taxonomy skills. (iv) Given the vast range of biodiversity in Australia and the broad host-specificity of Anisakis spp., particularly in the larval stages, the full range of their intermediate hosts remains unknown. (v) The health impacts of the infection of the intermediate/definitive hosts with Anisakis spp. are not fully understood. Thus, one of the important areas for future studies is investigating the pathogenicity of Anisakis spp. in affected animals. This is a crucial yet unknown factor for the conservation of some endangered species in Australia.

Parasite Fauna of the White-Streaked Grouper (Epinephelus ongus) from the Thousand Islands, Java, Indonesia

PURPOSE

Fish parasites can cause diseases in humans and lead to commercial losses in fisheries and aquaculture. The objectives of this study were to analyze E. ongus's parasite fauna regarding food safety and parasite transmission risk between Epinephelus species and test whether E.ongus populations can be distinguished by their parasite community.

METHODS

We studied the metazoan parasite fauna of 30 white-streaked groupers Epinephelus ongus from the Thousand Islands, Java Sea, Indonesia, and compared the parasite community with specimens from Karimunjawa archipelago, Java Sea, from a former study. We used common fish parasitological methods for fish examination and parasite calculations.

RESULTS

We found 12 metazoan parasite species, establishing five new host and five new locality records, increasing the known parasite fauna of E. ongus by 21%. No anisakid worms infected E. ongus. All but one (trematode Gyliauchen cf. nahaensis) species have been previously reported from Epinephelus. Parasite abundance of E. ongus differed significantly between the two regions.

CONCLUSIONS

Due to a certain degree of host specificity to groupers, there is potential risk of parasite transmission from E. ongus into groupers in mariculture or surrounding fishes, which increases (sea) food security related health risks from zoonotic parasites and calls for better monitoring and management plans for E. ongus. The regional separation of the Thousand Islands and Karimunjawa with different food availability and fish ecology causes different parasite abundances, distinguishing two separate E. ongus populations by their parasite fauna.

Occurrence and abundance of zoonotic nematodes in snapper Chrysophrys auratus, a popular table fish from Australian and New Zealand waters

In Australia and New Zealand (NZ), snapper Chrysophrys auratus is known for delicate mild flavoured flesh and is a favoured species to serve raw as sashimi or in sushi. The diet of snapper includes a variety of intermediate hosts of larval nematodes, and as a result, snapper has potential to become highly infected with zoonotic/non-zoonotic nematodes. The aims of this study were to survey nematodes in snapper from Australia and New Zealand waters and to identify nematode species using combined morphological and molecular methods. The zoonotic potential of nematodes identified in this study are discussed. A total of 112 snapper were purchased from the Sydney fish market, New South Wales, Australia. Fish were dissected and only the visceral content and digestive tract were examined for nematode infection. Parasites were initially identified by the microscopic method as four different types belonging to the families Anisakidae (Anisakis types I & III, and Terranova type II) and Cucullanidae (Dichelyne spp.). All Anisakidae nematodes were at infective stages. Species-level identification was actualised through sequencing of the internal transcribed spacer (ITS-1, 5.8S, ITS-2) regions. The Anisakis types I & III were confirmed as Anisakis pegreffii and A. brevispiculata, respectively of which A. pegreffii is considered globally as a zoonotic nematode. The specific identification of Terranova type II and Dichelyne spp. was not possible as no comparable sequence data were available in GenBank. The phylogenetic tree clustered Anisakis types I & III with A. pegreffii and A. brevispiculata, respectively; Terranova type II sequences as a separate clade with previously identified larval and adult Terranova and Pseudoterranova species. Based on phylogenetic analyses the present Cucullanid specimens were assigned herein as Dichelyne cf. pleuronectidis, and an unknown species Dichelyne sp. 1. This study represents the first host record globally for zoonotic Anisakid nematodes in this popularly consumed table fish and a new region record for D. cf. pleuronectidis and Dichelyne sp. 1. Further investigation is required, using more comprehensive parasite detection and recovery methods, to assess the health risk these nematodes may pose to human and fish health in Australia/NZ.

Effectiveness of Gutting Blue Whiting (Micromesistius poutassou, Risso, 1827), in Spanish Supermarkets as an Anisakidosis Safety Measure

Anisakidosis is a parasitic zoonotic disease which can cause gastroallergic reactions in humans. In 2010, the European Food Safety Agency estimated that approximately 20,000 cases of anisakiasis had been reported across the world, with Spain having the highest number of infections in Europe. The blue whiting (Micromesistius poutassou, Risso, 1827) is one of the most widely fished species worldwide and represents around 25% of the white fish eaten in Spain. The Spanish Food Safety Authority requires obligatory evisceration of certain fish species before commercialization, but not for blue whiting. Nevertheless, some supermarkets carry this out themselves to prevent human infections and negative customer reactions deriving from the presence of ascaridoid larvae. To assess the effectiveness of eviscerations at supermarkets, a total of 320 blue whiting specimens were examined. The risk of larval migration from the visceral cavity to the musculature in gutted and ungutted fish was also assessed. Our results showed a total prevalence (25%) of ascaridoids in fish gutted at the supermarket, and a direct relationship was found between the presence of larvae in the muscle and time until evisceration. In ungutted fish, the standard length and weight were higher for infected than for non-infected fish. Also, massive infections had a higher prevalence in these larger specimens, in which the viability of larvae was also high. Larval viability was not found to be affected by a 24-h refrigeration period. Anisakis was the most prevalent genus identified in the fish examined. The results indicate that gutting at the supermarket is not an effective method for the total removal of ascaridoid larvae and that additional safety measures are advisable.

Species composition and infection levels of Anisakis (Nematoda: Anisakidae) in the skipjack tuna Katsuwonus pelamis (Linnaeus) in the Northwest Pacific

Parasites can be used as biological tags to assess stock structures in various marine fish species. In the present study, the species composition and infection levels of parasitic nematodes of the genus Anisakis in the skipjack tuna Katsuwonus pelamis were examined in the Northwest Pacific and adjacent seas. A total of 867 third-stage larvae of Anisakis were collected from 112 skipjack tunas captured around Japan and in other subtropical localities. All larvae were identified as A. berlandi, A. pegreffii, A. simplex (s.s.), A. typica, and A. physeteris (s.l.) by the direct sequencing of the mitochondrial cox2 gene and real-time PCR assays targeting the nuclear ITS region. Anisakis species composition differed among northeastern Japan, the Sea of Japan, and other areas (central Japan, the Nansei Islands, and subtropical region), which is largely concordant with previous stock discrimination of skipjack tuna. Molecular phylogenetic analysis resulted in two intraspecific genetic groups in A. simplex (s.s.), one of which occurred almost exclusively in northeastern Japan. This could be a useful indicator for stock discrimination. Skipjack tunas from northeastern Japan were also characterized by a remarkable variety in the intensity of A. simplex (s.s.), suggesting the commingling of individuals with different migration patterns. This idea might be further justified by the geographic distribution of two genetically distinct groups of A. physeteris (s.l.).

Insights into the role of deep-sea squids of the genus Histioteuthis (Histioteuthidae) in the life cycle of ascaridoid parasites in the Central Mediterranean Sea waters

Ascaridoid nematodes comprise a wide range of heteroxenous parasites infecting top fish predators and marine mammals as definitive hosts, with crustaceans, squids, and fishes acting as intermediate/paratenic hosts. Limited data exist on the species and role of several intermediate and paratenic hosts in the life cycle of these parasites. In the aim of adding knowledge on the role of squid species in their life cycle, we have here investigated the larval ascaridoid nematodes collected from the deep-sea umbrella squid Histioteuthis bonnelli and the reverse jewel squid Histioteuthis reversa captured in the Central Mediterranean Sea (Tyrrhenian Sea). Morphological study and sequence analysis of the internal transcribed spacer (ITS) regions of the ribosomal DNA (rDNA) and the mitochondrial cytochrome c oxidase subunit 2 (mtDNA cox2) gene locus revealed the occurrence of Anisakis physeteris and of an unidentified species of the genus Lappetascaris. Sequence analysis revealed that specimens of Lappetascaris from both squid species matched at 100% sequences previously deposited in GenBank from larval ascaridoids collected in octopuses of the genus Eledone of the Mediterranean Sea. The Bayesian inference tree topology obtained from the analysis of the fragments amplified showed that Lappetascaris specimens were included in a major clade comprising Hysterothylacium species collected in fishes of the families Xiphiidae and Istiophoridae. As regards the site of infection in the squid host species, A. physeteris larvae predominated (60.7%) in the gonads, while those of Lappetascaris (76.3%) were found infecting the mantle musculature. The overall high values of parasitic load suggest both squid species as transmitting hosts of third stage larvae of Lappetascaris to top predator fishes, as well as the umbrella squid as an intermediate/paratenic host in the life cycle of A. physeteris in the Mediterranean Sea.

The occurrence and abundance of infective stages of zoonotic nematodes in selected edible fish sold in Australian fish markets

Seafood is nutritious and a healthy source of proteins and its regular consumption is highly recommended by medical professionals and dieticians. Owing to this, the global consumption of seafood per capita has been significantly increasing since the 1960s. Consequently, seafood-borne pathogens, including parasites, have also become more widely known and recognised. In Australia, a vast island country, information about such parasites is extremely limited. This study aimed to determine the prevalence and abundance of zoonotic parasites, including anisakid nematodes, in selected Australian edible fish. Four species of fish, namely tiger flathead, Platycephalus richardsoni (n = 43), blue mackerel, Scomber australasicus (n = 117), snapper, Pagrus auratus (n = 11) and school whiting, Sillago flindersi (n = 90) were purchased from a fish market. Although a range of parasites was found, due to their significance for human health, the focus of this study was on nematodes whose infectious stage was found in these fish. The prevalence of nematodes in these fish species was 86.05%, 64.10%, 45.45% and 56.67%, respectively. Among the parasites found, Anisakis spp., Contracaecum spp. and Hysterothylacium spp. in tiger flathead, blue mackerel and school whiting, might be of zoonotic importance. Our findings suggest there is a need to revise current seafood safety protocols and develop educational campaigns for seafood industries stakeholders.

Integrative species delimitation and community structure of nematodes in three species of Australian flathead fishes (Scorpaeniformes: Platycephalidae)

This study aimed to determine the integrative characterisation of nematodes from three species of edible flathead fishes (Scorpaeniformes: Platycephalidae) in New South Wales, Australia, and describe nematode communities within three species of flatheads. Tiger (Platycephalus richardsoni (Castelnau); n = 20) and sand flatheads (Platycephalus bassensis (Cuvier); n = 20), sourced from the Nelson Bay area, and dusky flathead (Platycephalus fuscus (Cuvier); n = 20) from the Manning River, Taree, were examined for the presence of nematodes. The nematodes were initially classified morphologically as 12 different morphotypes belonging to the families Anisakidae (Anisakis types I, II, and III, Contracaecum type II, Terranova types I and II), Raphidascarididae (Hysterothylacium types IV, VI, VIII, and H. zhoushanense larva), and Gnathostomatidae (Echinocephalus sp. larva), Capillariidae (Capillaria sp.), followed by genetic identification through sequencing of the internal transcribed spacer (ITS-1, 5.8S, ITS-2) regions. Phylogenetic analyses revealed the evolutionary relationship between the identified larval specimens in the present study with available GenBank larval and adult nematodes. Sand flathead was 90% infected with nematodes followed by tiger flathead at 85% and dusky flathead at 15%. Nematodes infecting estuarine dusky and oceanic sand and tiger flatheads contrasted markedly. The analysis of similarities (ANOSIM) showed significant differences (p < 0.001) in the composition of taxa within nematode communities between the three species of flatheads (global R = 0.208) with the highest difference being between sand and dusky flatheads (R = 0.308, p < 0.001). The findings of the present study provide a foundation for future investigations of the community composition, life cycles, and distribution of nematode populations in edible fish in Australia and explore and clarify their significance to public health.

Contracaeciasis in an American white pelican

An American white pelican migrating through Iowa, USA exhibited regurgitation and anorexia. At the time of necropsy, numerous nematodes were observed in the crop and proventriculus with evidence of proventriculitis. Nematodes were identified as Contracaecum spp. based on morphological features of the adult worms and eggs. Species level identification of C. fagerholmi were made using nucleotide sequence analysis of the partial cox2 gene. Contracaecum infections are highly prevalent in piscivorous birds that acquire the infection by ingesting fish infected with larval stages of the parasite. Considering the possible zoonotic nature of Contracaecum, humans whose diets include uncooked fresh-water and/or marine fish should handle fresh fish with care, as these may harbor immature stages of Contracaecum spp.

Infection and molecular identification of ascaridoid nematodes from the important marine food fish Japanese threadfin bream Nemipterus japonicus (Bloch) (Perciformes: Nemipteridae) in China

The Japanese threadfin bream N. japonicus (Bloch) (Perciformes: Nemipteridae) is an important marine food fish in Asia. However, our present knowledge of the occurrence of its nematode parasites is still limited. In the present study, the species composition and infection rate of ascaridoid nematodes in N. japonicus from the South China Sea, were studied for the first time. Five ascaridoid species, namely Anisakis typica (L3), Hysterothylacium amoyense (L3), Hysterothylacium sp. IV-A (L3), adult of H. thalassini and Raphidascaris lophii (L3), were identified using integrative taxonomy. Hysterothylacium amoyense was the most prevalent species (prevalence 47.2%, mean intensity 14.9 ± 17.1). Hysterothylacium thalassini and R. lophii were reported in the Japanese threadfin bream for the first time. Two different genotypes of A. typica (overall prevalence of 3.4%; mean intensity 1.7 ± 0.9) were found in the South China Sea for the first time. The unique restriction polymorphism patterns of three species of Hysterothylacium are provided for rapid diagnosis. Our present results indicate that RFLP analysis of ITS region, using the restriction enzymes HhaI and RsaI, represents a simple and practical method for large-scale surveys of Hysterothylacium for seafood industry.

Morphological and molecular identification of Hysterothylacium larvae (Nematoda: Raphidascarididae) in marine fish from Tunisian Mediterranean coasts

The taxonomy of Hysterothylacium genus in Mediterranean waters remains incomplete and unresolved. The aim of the current study was to investigate the morphological and molecular identification of selected species of Hysterothylacium larvae in marine fish from the Tunisian Mediterranean coasts. A total of 192 marine fish samples were examined. In total, thirty-seven third-stage larvae of Hysterothylacium were morphologically identified as Hysterothylacium type V. In the present study, representatives of this type from the Mediterranean Sea were genetically characterized for the first time by sequencing the rDNA ITS (ITS1-5.8S-ITS2) regions and mtDNA cox2 gene. This study represents the first report of Hysterothylacium type V from the Mediterranean Sea. We also report Mullus barbatus, M. surmuletus, and Pagellus erythrinus as new hosts for this larval type. Based upon molecular and phylogenetic analyses considering the rDNA ITS regions, the Hysterothylacium type V described here was classified as a new genotype, named Genotype B. The valid genetic data of the described Hysterothylacium type V in the present study can be used to establish the phylogenetic relationships among Hysterothylacium species from the Mediterranean Sea and worldwide for future research.

Identification and genetic characterization of Contracaecum sp. (Nematoda Anisakidae) from China

Contracaecum species are economically important fish-borne larval nematodes with zoonotic significance. In June 2019, more than one hundred piscivorous birds were died in its habitats close to the Wild Duck Lake, located in Yanqing, northwest of Beijing, China. Post-mortem examination of Black Night Herons (Nycticorax) revealed the presence of numerous anisakid nematodes in the proventriculus. Recovered nematodes were identified as Contracaecum sp. based on morphological description. Phylogenetic analysis of the mitochondrial (mt) genome and the ITS gene showed that sequences of Contracaecum sp. Beijing isolates were grouped into a new individual cluster. Furthermore, the parasite was successfully isolated from fresh dead birds, feces of piscivorous birds, and fish and prevalence ranged from 8.0% to 81.8%. Consequently, our study demonstrated the Contracaecum sp. infections in different sources from China, which might constitute a threat to wildlife, aquaculture, and public health. This article is protected by copyright. All rights reserved.

Some adult and larval nematodes from fishes off New Caledonia

A collection of nematodes from the Muséum National d'Histoire Naturelle (National Museum of Natural History), Paris, France, was studied. The nematodes had previously been collected from a range of marine fish hosts. The aim of this study was to investigate the identity of these nematodes. Detailed body measurements of the nematodes were taken via light microscopy and where possible first and second internal transcribed spacers (ITS-1 and ITS-2) of ribosomal DNA were subjected to PCR, purified and sequenced. Six species and three larval types were found from a range of fish species and included 13 new host records and two new geographical records. Of the taxa found, Hysterothylacium kajikiae is the only species which may have zoonotic potential. The majority of host fish in this study are edible species, commercially and recreationally fished and frequently incorporated into the cuisine of New Caledonia as raw fish dishes. This study will allow better understanding of the diversity, life cycles, distribution and host-parasite relationships in the New Caledonia area.

Description and genetic characterisation of Pulchrascaris australis n. sp. in the scalloped hammerhead shark, Sphyrna lewini (Griffin & Smith) in Australian waters

Being listed in the IUCN Red List of Threatened Species, knowledge on the biology, health and diseases of the scalloped hammerhead, Sphyrna lewini (Griffith & Smith) is limited; this is especially true for its parasites. In this paper, a new species, Pulchrascaris australis, is morphologically described followed by genetic characterisation based on the sequence of the ITS region. The new species can be easily differentiated from its congeners based on the morphology of the mouthpart, spicules, plectanes, eggs and vulva. Phylogenetic analyses clearly distinguish specimens in the present study from other parasitic nematodes found in the Australasian waters and elsewhere. The sequencing data also suggest that Terranova larval type I found previously in various fish from New Caledonian and Australian (Queensland) waters also belong to Pulchrascaris australis n. sp.

Seafood-borne parasites in Australia: human health risks, fact or fiction?

Seafood is an increasingly popular source of healthy protein. Since 1961, the average annual increase in global food fish consumption has been twice as high as population growth and exceeds the consumption of meat from all terrestrial animals combined1. The following overview of seafood safety concerns is intended to help readers to understand potential risks associated with parasites in seafood products and the need for a national approach to reduce or minimise them. It is important to note that parasite infections are not limited to seafood: all other types of foods, including vegetables and red meat can also be infected with a broad range of parasites, some of which are more dangerous than parasites in seafood. The main issue is lack of science based contemporaneous safety protocols which focus on seafood-borne parasites. As a result, in Australia regulatory control of parasites in seafood lags far behind other food sectors. Seafood safety is a broad topic. The focus of this article is on an understudied field in Australia, seafood-borne parasitic diseases. The word ‘seafood' in this context encompasses fish and shellfish products from marine and freshwater ecosystems that are, directly or indirectly, meant for human consumption.

Zoonotic nematode parasites infecting selected edible fish in New South Wales, Australia

Despite increases in the annual consumption of seafood in Australia, studies on the occurrence and prevalence of zoonotic parasites in fish and the risk they may pose to human health are limited. The present study was aimed at determining the occurrence of zoonotic nematodes in commonly consumed fish in New South Wales, Australia's most populous state. Three species of fish, including the Australian pilchard, Australian anchovy, and eastern school whiting, were purchased from a fish market and examined for the presence of nematode parasites. All Australian pilchards examined in this study were infected (100%; n = 19), followed by the eastern school whiting (70%; n = 20) and Australian anchovy (56%; n = 70). Nematodes were in the larval stage and, therefore, classified by morphotype, followed by specific identification through sequencing of their internal transcribed spacer (ITS) regions. Seven different larval types with zoonotic potential, belonging to the families Anisakidae (Contracaecum type II and Terranova type II) and Raphidascarididae (Hysterothylacium types IV [genotypes A and B], VIII, XIV and a novel Hysterothylacium larval type, herein assigned as type XVIII), were found. The new larval type was identified as Hysterothylacium thalassini, based on ITS sequence data. The presence of the infective stage of a range of zoonotic parasites in fish commonly consumed in New South Wales is important, particularly as, in some dishes, these fish are used whole, raw or undercooked. This study provides the basis for future research on other aspects of these parasites, in regards to public health.

Description and characterisation of Terranova pectinolabiata n. sp. (Nematoda: Anisakidae) in great hammerhead shark, Sphyrna mokarran (Rüppell, 1837), in Australia

Terranova pectinolabiata n. sp. is described from the great hammerhead, Sphyrna mokarran, from Australian waters. This represents the first report of a species of Terranova from the host species. The new species is characterised by the morphology of the caudal plates and labia. ITS sequences were obtained for 20 specimens which were identical, despite morphological variation that has traditionally been indicative of separation of species. Additionally, genetic analyses confirmed the identification of the larval Terranova Type II previously reported in Australian and New Caledonian waters as Terranova pectinolabiata n. sp.

On the occurrence and molecular identification of Contracaecum larvae (Nematoda: Anisakidae) in Mugil cephalus from Turkish waters

Anisakis and Contracaecum species are fish borne zoonotic nematodes. In our previous studies, other larval anisakid and raphidascarid nematodes, Anisakis and Hysterothylacium species, were genetically identified in marine fish from Turkish waters. However, there is no information on molecular identification of larval Contracaecum species in marine fish from Turkey. Therefore, the aim of this study was only to investigate the presence and molecular identification of Contracaecum species in commonly commercialized marine fish from Turkish waters. A total of 475 marine fish, which belong to 21 different species, were sampled from the Aegean (FAO 37.3.1), Mediterranean (FAO 37.3.2), and Black Sea (FAO 37.4.2). The prevalence of Contracaecum L3 larvae in the Aegean Sea was identified as 10% in Mugil cephalus. All Contracaecum L3 larvae were molecularly characterized with RFLP targeting the ITS region and rrnS gene. Moreover, all larvae were analyzed by sequencing of ITS region, rrnS and cox2 gene. All Contracaecum larvae were identified as C. overstreeti based on the cox2 sequence analysis. This is the first report of C. overstreeti larvae in M. cephalus as paratenic and intermediate hosts. Furthermore, the analysis reveals novel information on ITS region. Additionally, the rrnS gene of C. overstreeti was also achieved and deposited in Genbank for the first time. The PCR-RFLP patterns of the ITS region and rrnS gene from C. overstreeti were presented in the present study. Consequently, the presence of C. overstreeti larvae in M. cephalus from the Aegean Sea may also potentially capable of inducing allergic sensitization in humans.

Seafood-Borne Parasitic Diseases: A “One-Health” Approach Is Needed

Global consumption of seafood is steadily increasing, as is the variety of seafood, including dishes with raw or undercooked fish, leading to an increased risk of seafood-borne parasitic diseases. To address today’s challenges to understand the biology and ecology of these parasites in an ever-changing environment and to tackle their pathogenicity, multidisciplinary research is needed. In addition, the gap between research and stakeholders must be bridged to decrease the risk these parasites pose to public health. A “One-Health” approach to research is necessary to ensure that consumers, aquatic animals, and environmental health questions are assessed in an integrated and holistic manner, resulting in a more comprehensive understanding of the issues associated with seafood-borne parasitic diseases and potential solutions. However, when it comes to seafood-borne parasitic diseases, there is limited guidance available for a “One-Health” approach since these diseases can be less known. In this article, the focus is on parasitic diseases caused by seafood, which have been less studied even in some developed countries where seafood is popular. A brief overview of some of the seafood-borne parasitic diseases is provided followed by the significance of the awareness among various stakeholders in a country. In this article, it is argued that researchers and stakeholders are closely connected and a knowledge gap in one can result in a gap in knowledge and awareness in the other, causing an inability to accurately estimate the issues caused by these parasites. It is suggested that raising awareness, supporting research and training of all stakeholders are crucial for the prevention of seafood-borne parasitic diseases and the protection of the health of seafood consumers.

Parasite loss or parasite gain? Story of Contracaecum nematodes in antipodean waters

Contracaecum spp. are parasitic nematodes belonging to the family Anisakidae. They are known to be able to have highly pathogenic impacts on both wildlife (fish, birds, marine mammals) and humans. Despite having the most numerous species of any genus of Anisakidae, and despite a wide range of publications on various aspects of their pathogenicity, biology and ecology, there are no recent comprehensive reviews of these important parasites, particularly in the Southern Hemisphere. In this article, the diversity of Contracaecum parasites in Australian waters is reviewed and possible anthropological impacts on their populations are discussed. The abundance and diversity of these parasites may have been under-reported due to the inadequacy of common methods used to find them. Populations of Contracaecum parasites may be increasing due to anthropogenic factors. To minimise the risk these parasites pose to public health, preventive education of stakeholders is essential. There are still many unknown aspects of the parasites, such as detailed information on life cycles and host switching, that will be interesting directions for future studies.

Morphological and genetic characterization of Hysterothylacium Ward & Magath, 1917 (Nematoda: Raphidascarididae) larvae in horse mackerel, blue whiting and anchovy from Spanish Atlantic and Mediterranean waters

The presence of zoonotic Hysterothylacium larvae in fish from Spanish Atlantic and Mediterranean waters, which can cause economic losses for commercial fisheries, has been reported in several studies; however, little is known about species identity in this region. The aim of this study was to identify at species level the Hysterothylacium morphotypes detected in three commonly consumed fish: horse mackerel (Trachurus trachurus), blue whiting (Micromesistius poutassou) and anchovy (Engraulis encrasicolus). Third- and fourth-stage Hysterothylacium larvae, as well as adults obtained from larval in vitro culture, were morphologically and molecularly identified by ITS1/ITS2 rDNA sequencing. Four Hysterothylacium morphotypes were detected. Genetic analysis showed that morphotypes VIII and IX were different larval stages of Hysterothylacium aduncum, which was supported by cultured adult species identification. Morphotypes III and IV were found to correspond to different developmental stages of another species of Hysterothylacium. As all larval types detected were morphologically indistinguishable from others previously reported yet showed clear genetic differences, they are referred here as new genotypes. This is the first time that ITS-sequence data of various developmental stages of the same species, including adults, have been studied and compared, providing crucial knowledge for future studies on Hysterothylacium identification and biology.

Occurrence of anisakid parasites in marine fishes and whales off New Caledonia

Anisakid nematodes are the most infamous parasites occurring in seafood with ability to infect humans. In the present study, the infective stages of five anisakid larval types, including Anisakis types I and III, Terranova types I and II and Contracaecum larval type, as well as adult Anisakis paggiae are reported from 16 host species from New Caledonian waters. The specific identity of the larval types was investigated using ITS sequence data. Anisakis larval types I and III were identified as Anisakis typica and Anisakis brevispiculata, respectively, based on identical ITS sequences. However, the specific identity of the Terranova larval types and Contracaecum larval type remains unknown until a matching ITS sequence from a well-identified adult is available. Several fish host species are reported for the first time for anisakid larval types found in this study. Considering that third-stage larvae of anisakids are known to be the infective stage of the parasite for humans and the popularity of seafood in New Caledonia, presence of these parasites in New Caledonian fish is of high importance in terms of public health and raising awareness among various stakeholders. Although adult nematodes in the present study were identified as Anisakis paggiae, the spicule length is shorter in our specimens and falls within the range reported for Anisakis oceanicus previously reported in Pacific waters from black fish (genus Globicephala) and later synonymised with Anisakis physeteris. However, our specimens are different from A. physeteris in morphology of ventriculus. Anisakis paggiae has been reported from whales in southern hemisphere and this is the first report from the Pacific regions.