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

18S rRNA gene metabarcoding for investigation of gastrointestinal parasite diversity in great cormorants

The great cormorant (Phalacrocorax carbo) is a migratory, fish-eating bird that may act as a carrier for various pathogens, raising potential ecological and public health concerns. This study investigated the diversity of gastrointestinal parasites in great cormorants from the Republic of Korea using 18S rRNA gene metabarcoding and conventional diagnostic methods. Fecal samples were collected from 10 great cormorants in Korea, and DNA was extracted for metabarcoding targeting the V4 and V9 regions of the 18S rRNA gene using the MiSeq platform. Conventional PCR and microscopic examination were used for validation. The V4 region of the 18S rRNA gene revealed the presence of Baruscapillaria spiculata, Contracaecum sp., and Isospora lugensae. The V9 region analysis identified the following parasites: Tetratrichomonas sp., Histomonas meleagridis, Trichomitus sp., Tetratrichomonas prowazekii, B. obsignata, Monosiga ovata, and Fasciola gigantica. Furthermore, conventional PCR confirmed the presence of Contracaecum sp., Isospora sp., and unspecified trichomonads, and microscopic examination identified eggs of capillarid, Contracaecum, and Eustrongylides and trophozoites of flagellated protozoa in the collected cormorant fecal samples. The findings underscored the potential ecological role of great cormorants as hosts for diverse gastrointestinal parasites and the utility of 18S rRNA gene metabarcoding for screening the diversity of gastrointestinal parasites in great cormorants.

Case Report: The first record of Eustrongylides sp. infection in the Chinese alligator (Alligator sinensis)

Although digestive tract parasites are widely spread in wild or farmed crocodiles worldwide, only limited data are available on Eustrongylides sp. reported in crocodiles. The Chinese alligator (Alligator sinensis) is endemic to the Yangtze River in China, and only a few parasites have been reported to infect the Chinese alligator. In this study, a nematode was collected in the abdominal fascia of a captive deceased Chinese alligator. Cytochrome oxidase I (COI), internal transcribed spacer region (ITS) and partial small subunit DNA segments (18S) sequences were amplified to further confirm the genetic information of the species. The results showed that the nematode was attributed to the genus Eustrongylides. Overall, this is the first report of Eustrongylides sp. infected in the Chinese alligator, expanding the known host range of this nematode and contributing to a better understanding of its life cycle.

Histopathological, morphological, and molecular characterization of fish-borne zoonotic parasite Eustrongylides Excisus infecting Northern pike (Esox lucius) in Iran

Eustrongylides excisus is a fish-borne zoonotic parasite known to infect various fish species, including Northern pike (Esox Lucius). This nematode, belonging to the family Dioctophymatidae, has a complex life cycle involving multiple hosts. This study aimed to investigate the occurrence of Eustrongylides nematodes in Northern pike (E. Lucius) collected from Mijran Dam (Ramsar, Iran). Between June and October 2023, an investigation was conducted on Northern pike from Mijran Dam in Ramsar, Iran, following reports of reddish parasites in their muscle tissues. Sixty fish were examined at the University of Tehran, revealing live parasites in the muscles, which were then analyzed microscopically and preserved for a multidisciplinary study. The skeletal muscle tissues of 85% (51/60) of fish specimens were infected by grossly visible larvae which were microscopically identified as Eustrongylides spp. In histopathological examination, the lesion was composed of encapsulated parasitic granulomatous myositis. Microscopically, the cystic parasitic granulomas compressed the adjacent muscle fibers, leading to their atrophy and Zenker's necrosis. Moreover, epithelioid macrophages, giant cells and mononuclear inflammatory cells were present around the larvae and between the muscle fibers. Finally, a molecular analysis by examining the ITS gene region, revealed that they belong to the species E. excisus. Eustrongylidiasis in northern Iran necessitates further research into the biology, epidemiology, and control of Eustrongylides nematodes, focusing on various hosts. This study is the first to comprehensively characterize E. excisus in Northern pike in Ramsar, Iran, raising concerns about possible zoonotic transmission.

Unregulated introduced fish (Perca fluviatilis Linnaeus, 1758) is host to zoonotic parasites in a small Mediterranean island

Introduced species have a major impact on freshwater ecosystems, particularly on islands. Numerous fish species have been introduced in Corsica (Mediterranean island, southern France) as part of planned programs or clandestinely. The introduction of non-native freshwater fish species can have a range of impacts on the recipient ecosystem, including through the co-introduction of its pathogens. A sample of introduced perch Perca fluviatilis Linnaeus, 1758 from the artificial reservoir of Padula was examined following a report of parasites by an angler. The analyses revealed the occurrence of Eustrongylides sp. (Nematoda) and Clinostomum complanatum (Digenea), two zoonotic parasites in P. fluviatilis. Both parasites are reported for the first time in France. Eustrongylides sp. and C. complanatum may have been introduced with their fish intermediate hosts or through their final bird hosts. The occurrence of the two parasites raises concerns from both a veterinary and human health perspective as they can use a wide range of amphibians as intermediate hosts and can be acquired in humans through the consumption of raw or undercooked fish.

High prevalence and concomitant infection of Ranavirus and Eustrongylides sp. in the invasive American Bullfrog in Brazil

American Bullfrogs, Aquarana catesbeiana, are invasive anuran species distributed worldwide. One of the adverse impacts that this species causes in native communities is as a reservoir host for pathogens and parasites. Here, we report the coinfection of two pathogenic organisms in A. catesbeiana: Ranavirus and the nematode Eustrongylides. Bullfrogs were collected in the wild in a pond close to the urban area of São Paulo, Brazil. The prevalence of both pathogens was high: 77% were infected with ranavirus with a mean viral load of 1010.3 viral copies, and 100% of the bullfrogs were infected by Eustrongylides sp. with a mean intensity of infection of 13.4 specimens per host. Four host specimens (31%) presented pathological signs that seemed to be related to the Eustrongylides sp. infection, such as internal organs adhered to each other due to high intensity and large size of the nematodes, ulcers, and raw flesh wounds caused by the nematode. The pathogenic and concomitant infections have potential zoonotic implications and raise concerns about human infection risks for Eustrongylides infection. Moreover, such infections may represent an additional level of threat to native communities through the potential shifts in patterns of parasite and pathogen transmission. Future research involving the native anuran community is essential to ascertain whether invasive bullfrogs are attenuating or exacerbating diseases such as ranavirosis and eustrongylidiosis.

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.

The Occurrence of Freshwater Fish-Borne Zoonotic Helminths in Italy and Neighbouring Countries: A Systematic Review

In recent years, the consumption of fish products has surged in European countries, being an essential part of a healthy diet. Despite representing a small part of EU production, freshwater fisheries hold considerable significance for lake-dwelling populations and tourists seeking traditional dishes. This increased fish consumption has brought to light potential health risks associated with fish-borne zoonotic helminths (FBZHs), now acknowledged as global food-borne parasites. Fish-borne zoonotic helminths belong to various taxonomic groups, including nematodes (Anisakidae), trematodes (Opisthorchiidae and Heterophyidae), and cestodes (Diphyllobothriidae). More than 50 species of FBZH are known to cause human infections, derived from eating raw or undercooked aquatic foods containing viable parasites. Despite increased attention, FBZHs remain relatively neglected compared to other food-borne pathogens due to factors like chronic disease progression and under-diagnosis. This systematic review concentrates on the prevalence of six freshwater FBZHs (Clinostomum complanatum, Contracaecum rudolphii, Dibothriocephalus latus, Eustrongylides excisus, Opisthorchis felineus, and Pseudamphistomum truncatum) in Italy and neighbouring countries. The study explores the expansion of these parasites, analysing their biological and epidemiological aspects, and the factors that influence their proliferation, such as the increased cormorant population and the lake eutrophication phenomena. In summary, this research highlights the necessity for further research, the development of spatial databases, and the establishment of a unified European policy to effectively manage these multifaceted health concerns. It strongly advocates adopting a One-Health approach to address the growing incidence of parasitic zoonoses within the context of food safety in EU countries.