Mapping the occurrence of Eustrongylides spp. in fish species caught from six lakes in Central Italy (Tuscany and Latium regions): Implications for local fishery supply chains

In the present study, in order to expand the knowledge on the distribution of parasites of the genus Eustrongylides in never investigated Italian lacustrine areas of Tuscany and Latium, fish specimens from four Tuscan lakes (Bilancino, Chiusi, Montedoglio and San Cipriano) and two Latium lakes (Bolsena and Bracciano) were collected and analyzed. The parasitological analysis, consisting of a visual inspection followed by a chloro-peptic digestion, was performed on 1650 specimens belonging to 17 species: European perch (Perca fluviatilis), Pumpkinseed (Lepomis gibbosus), Pike-perch (Sander lucioperca), Largemouth black bass (Micropterus salmoides), Pike (Esox lucius), Big-scale sand smelt (Atherina boyeri), Tench (Tinca), European Whitefish (Coregonus lavaretus), Channel catfish (Ictalurus punctatus), Chub (Squalius cephalus), Rudd (Scardinius erythrophthalmus), Common bleak (Alburnus alborella), South European roach (Sarmarutilus rubilio), South European nase (Protochondrostoma genei), Italian riffle dace (Telestes muticellus), Goldfish (Carassius auratus), and Freshwater bream (Abramis brama). Eustrongylides spp. larvae were only found in one specimen of European perch caught in Bracciano Lake and purchased from a local fishmonger (P = 3.3%; MI = 1; MA = 0.03). The only isolated Eustrongylides spp. larva was submitted to molecular analysis of the ITS gene region and identified as E. excisus. This finding adds Bracciano Lake to the list of the several Italian lakes in which nematodes belonging to this genus have been reported. Even if the observed prevalence is currently low, the presence of the parasite in this local freshwater fish supply chain requires FBOs to adopt risk management measures to prevent contaminated products from reaching final consumer. Moreover, future investigations will show if the parasite expands in these areas.

Occurrence and characterisation of Eustrongylides species in Australian native birds and fish

In Australia, nematodes belonging to the genus Eustrongylides were believed to be endemic species until the late 20th century when they were all considered to be E. excisus, invalid or inquirendae. Although these nematodes have frequently been reported in Australian fish, reptiles, and birds and cause disease or mortality among them, there has been no attempt to date to characterise them genetically. Globally, also, no one has validated or defined suitable genetic markers to distinguish between species of Eustrongylides. In this study, adult Eustrongylides from little black cormorant (Phalacrocorax sulcirostris; n = 3) and larvae from mountain galaxias (Galaxias olidus, n = 2) and a Murray cod (Maccullochella peelii, n = 1), and a Murray cod-trout cod hybrids (Maccullochella peelii x Maccullochella macquariensis, n = 1) were available for morphological examination and molecular characterisation. The adult nematodes from cormorants were identified as E. excisus. Sequences of the 18S and ITS regions were then obtained for all nematodes, which were identical among all specimens (larvae and adults) and also identical to those of E. excisus available in the GenBank. However, only one base pair difference exists between the 18S sequences of E. excisus and E. ignotus, with limited sequences available in GenBank accompanied with proper morphological data for the nematodes. With that limitation in mind, identifying our specimens as E. excisus suggests spill-over - that it is an introduced parasite species that has successfully established its life cycle among Australian native species - may have occurred. Our study is the first report of E. excisus in the little black cormorant, P. sulcirostris. Our results do not exclude the possibility of the occurrence of other species of Eustrongylides, either native or exotic, in Australia. This parasite is zoonotic and with increasing demand for fish and changing dietary preferences, such as the consumption of raw or undercooked fish, its occurrence in the flesh of the fish is concerning. This parasite is also associated with anthropogenic habitat alteration affecting the reproductive success of the infected hosts. Therefore, awareness among the relevant authorities of the presence of the parasite in Australia and its adverse impact on native animals is crucial for the success of conservation plans such as fish recovery and relocation efforts.

Identification of Larval Eustrongylides (Nematoda: Dioctophymatoidea) sp. from Channa punctata Bloch, 1793 by Morphological and Molecular Techniques

OBJECTIVE

This study aimed to identify the larval form of Eustrongylides sp. isolated from the visceral organs of Channa punctata (Bloch, 1793) using morphological and molecular methods.

METHODS

Fishes were collected from fish farms in Nadia and North 24 Paraganas for the collection of nematodes. The visceral organs were dissected and kept in 0.67% normal saline. Nematodes collected from the abdominal regions and visceral organs for light microscopy study were fixed in 70% ethanol. Morphological features were studied by placing the nematodes in lactophenol. The specimens were later preserved in 70% ethanol containing 5% glycerine. Specimens processed for scanning electron microscopy were fixed in 2.5% glutaraldehyde and postfixed in 1% osmium tetraoxide. Proper identification was done by using standard methology. Molecular studies were performed for the 18S rRNA, ITS1, 5.8S rRNA, ITS2 and 28S rRNA gene fragments using polymerase chain reaction amplification, sequencing and phylogenetic analysis.

RESULTS

The morphological characteristics of nematodes were described with the help of light and scanning electron microscopy. Additional features not described earlier like dimensions and shape of the cephalic papillae, absence of somatic papillae, presence of caudal papillae, were identified for the first time. Moreover, molecular studies with ITS regions further confirmed the identification of the nematode.

CONCLUSION

Thus the use of morphotaxonomy along with molecular techniques would help in proper identification of Eustrongylides sp infecting edible fish. Studies on the nematode would help toexplore the intermediate as well as paratenic hosts of the parasite. Data in this regard would contribute significantly to the fish database in regard to parasites infesting edible fishes.

Eustrongylides (Nematoda:Dioctophymatidae): Epizootology and Special Characteristics of The Development Biology

Eustrongylides spp. are the nematodes from the Dioctophymatidae family which are potentially dangerous for the mammal's heath. The first aim of the present research is to describe the biology, developmental characteristics and epizootology of the Eustrongylides spp. nematode. Eustrongylidosis is a parasitic disease commonly occurring in the countries with temperate continental, tropical and subtropical climate. The Eustrongylides spp. parasites are biohelmints with a complex life cycle. The development of the nematodes takes place in the aquatic environment and includes a vast range of intermediate, accidental and definitive hosts. It has also been reported in humans. The second aim of the research is to describe the clinical and pathomorphological changes in organs and tissues of the infected animals, and influence of biotic and abiotic factors on formation of the natural centers of spreading of eustrongylidosis; diagnostics of eustrongylidosis.

Distribution of the nematodes of the genus Eustrongylides (Nematoda, Dioctophymatidae) in the world

Eustrongylides spp. are nematodes from the Dioctophymatidae family, potentially dangerous for the health of mammals. The aim of this review is to describe the distribution of the Eustrongylides spp. nematode. Eustrongylidosis is a parasitic disease which is common in countries with a continental, tropical or subtropical climate. Eustrongylides are biohelminths with a complicated development cycle. The nematode development takes place in the aquatic environment and includes a wide range of intermediate, definitive, and accidental hosts. The purpose of this review is describe the distribution of Eustrongylides spp. nematodes in the global regions, describe the prevalence of infection in those regions, and identify intermediate, definitive, and accidental hosts. It was found that Eustrongylides spp. nematrodes are significantly widespread around the world. In part in North America the agent of eustrongylidosis is registered mostly among birds and fishes, but cases of humans being affected with the disease are noted as well. In South America the given disease was also registered among amphibians and reptiles. In Europe, Asia, Africa, Oceania and countries of the Far East, the disease is registered mostly in fishes, rarely – in birds. The taxonomic identification showed that some nematode species were related to certain geographic areas. For example, Eustrongylides ignotus and Eu. tubifex were mostly registered in North America, while for Europe (including Ukraine), Near and Middle East, Eu. еxcisus is a dominant species. Analysis of scientific sources showed that continents with warmer climatic conditions (South America, Asia, etc.) are characterized with a wider range of fishes, birds and reptiles which can potentially serve as hosts for the Eustrongylides nematodes.

Morphological and Phylogenetic Analysis of Eustrongylides sp. and Gnathostoma spinigerum Parasitizing the Asian Swamp Eel Monopterusalbus in China

Nematode infections transmitted to humans by the consumption of wild or cultured eels are increasingly being reported. In the present study, 120 Asian swamp eel, Monopterus albus (Zuiew), individuals collected from China were examined for parasite infections, and 78 larval nematodes were isolated. Morphological and molecular characteristics, including sequence and phylogenetic analysis of the internal transcribed spacer (ITS) and cytochrome c oxidase subunit I (COI) gene regions, were employed to identify these nematodes at the lowest taxonomic level possible. Asian swamp eel was infected with two zoonotic parasite taxa: Gnathostoma spinigerum advanced third-stage larvae, with 6.67% prevalence and mean intensity = 1.25, and Eustrongylides sp. fourth-stage larvae, with 26.67% prevalence and mean intensity = 2.13. These findings evidence the need to enhance public hygiene and food safety awareness toward eel consumption.

Morphological and molecular characterization of Eustrongylides excisus larvae (Nematoda: Dioctophymatidae) in Sander lucioperca (L.) from Northern Turkey

The genus Eustrongylides Jägerskiöld, 1909 includes parasitic nematodes (Dioctophymatidae) affecting various fish species and piscivorous birds of freshwater ecosystems. Currently, there is little information on the molecular characterization of E. excisus based on nuclear ribosomal internal transcribed spacer (ITS) rDNA regions. However, before the present study, there had been no reports of characterizing the E. excisus using nuclear small subunit ribosomal RNA (SSU rRNA) and mitochondrial cytochrome c oxidase subunit I (COI) genes sequences. In the present study, Eustrongylides spp. larvae were collected from pike-perch Sander lucioperca (L.) in Northern Turkey, and characterized by sequencing of ITS regions, SSU rRNA, and COI markers. Larvae herein morphologically identified as the fourth stage of Eustrongylides spp. were genetically identified as E. excisus based on the ITS sequence analysis. This study is the first record of SSU rRNA and COI sequences for E. excisus in GenBank. This is also a molecular characterization of E. excisus for the first time in Turkey. The ITS, SSU rRNA, and COI sequences of E. excisus can be used to establish the phylogenetic relationships of Eustrongylides species from Turkey and worldwide for further studies.

Eustrongylides sp. (Nematoda, Dioctophymatoidea) parasitizing Hoplias malabaricus (Actinopterygii: Erythrinidae) collected from the state of Rio de Janeiro, Brazil

Hoplias malabaricus (Characiformes, Erythrinidae), trahira, is a neotropical freshwater fish of economic and public health significance. A total of 45 specimens of H. malabaricus commercialized in the municipality of Magé, state of Rio de Janeiro, Brazil, were acquired between April 2016 and April 2018 to investigate the presence of nematode larvae. Twenty of the fish were found parasitized by 347 fourth-stage nematode larvae identified taxonomically as Eustrongylides sp. using morphological, morphometric and molecular data. The parasitic indices were: prevalence 44.44%, mean intensity 17.35, mean abundance 7.71, and range of infection 2-40. Infection sites were musculature, mesentery, abdominal cavity, and serosa of intestine, stomach and liver. This is the first report of Eustrongylides sp. larvae parasitizing H. malabaricus in the state of Rio de Janeiro.

Morphological and Molecular Characterization of Larval and Adult Stages of Eustrongylides excisus (Nematoda: Dioctophymatoidea) with Histopathological Observations

The genus Eustrongylides includes nematodes known as the etiological agent of the "big red worm disease." The aim of this work was to identify Eustrongylides spp. larvae from fish and adults from great cormorant (Phalacrocorax carbo) sampled at Lake Trasimeno, Italy, by morphological and molecular analysis. Histopathological description of the lesions in birds was also provided. We described adults of Eustrongylides excisus for the first time in Italy, and we also linked larval stages 3 and 4 to adults. The use of molecular tools combined with the traditional taxonomy will help the identification of the species, including species inquirendae. Moreover, molecular analysis can also help to investigate the role of intermediate and paratenic hosts, to deepen the knowledge about geographical distribution of the different Eustrongylides spp. and to define the zoonotic potential of E. excisus, which has not yet been identified as causal agent of human cases.