Expression of immune relevant genes in rainbow trout following exposure to live Anisakis simplex larvae

Rat and fish peripheral blood leukocytes respond distinctively to Anisakis pegreffii (Nematoda, Anisakidae) crude extract

Infective third-stage larvae (L3) of the marine nematode Anisakis pegreffii cause inflammation and clinical symptoms in humans, their accidental host, that subside and self-resolve in a couple of weeks after L3 die. To characterise the differences in an early immune response of a marine vs. terrestrial host, we stimulated peripheral blood leukocytes (PBLs) of fish (paratenic host) and rat (accidental, human-model host) with A. pegreffii crude extract and analysed PBL transcriptomes 1 and 12 h post-stimulation. Fish and rat PBLs differentially expressed 712 and 493 transcripts, respectively, between 1 and 12 h post-stimulation (false discovery rate, FDR <0.001, logFC >2). While there was a difference in the highest upregulated transcripts between two time-points, the same Gene Ontologies, biological processes (intracellular signal transduction, DNA-dependent transcription, and DNA-regulated regulation of transcription), and molecular functions (ATP and metal ion binding) were enriched in the two hosts, showing an incrementing dynamic between 1 and 12 h. This suggests that the two distinct hosts employ qualitatively different transcript cascades only to achieve the same effect, at least during an early innate immunity response. Activation of later immunity elements and/or a combination of other host's intrinsic conditions may contribute to the death of L3 in the terrestrial host.

Eye fluke effects on Danish freshwater fish: Field and experimental investigations

Eye flukes in fish are common in freshwater lakes. Fish become infected by the penetration of cercariae released from freshwater snails, and high infection pressures may be associated with mortalities in a Danish lake. Examination of two other freshwater lakes, combined with laboratory study, supported the notion. We investigated 77 freshwater fish from two lakes and the infection level suggested the occurrence of a high cercarial infection pressure in the Danish lakes. Dominant genera were Tylodelphys and Diplostomum covering a range of species identified by PCR and sequencing of the 18S (partial)-ITS1-5.8S-ITS2-28S (partial) of the rDNA. Cercariae of the prevalent species Diplostomum pseudospathaceum were used to infect zebrafish Danio rerio for the elucidation of short-term effects on the fish host. Zebrafish did not display abnormal behaviour when exposed to 200-400 cercariae, but a dosage of 600 and 1,000 cercariae/fish proved lethal. When fish were exposed to sublethal dosages, 19 out of 27 immune genes were significantly regulated and three genes encoding cytokine (IL 4/13B, IL-6 and IL-8) were upregulated at 3 hr post-infection (hpi), whereas others were downregulated especially at a later time point. We suggest that direct massive cercarial penetration of fish surfaces may be detrimental and may represent a threat to fish populations.

Intrinsic properties of anisakid nematode larvae as a potential tool for the detection in fish products

Anisakid nematode larvae (NL) in fish products comprise a risk to human health and, if visible, lead to the rejection of these products by consumers. Therefore, great efforts are being made for the identification of these anisakid larvae to estimate the potential consumer health risk as well as to develop effective detection methods in order to prevent the introduction of heavily infected fish products into the market. The tasks of national reference laboratories include the improvement of detection methods and to promote their further development. As a prerequisite for improved detection, it is important to understand the structural properties of anisakid NL and compounds produced during host-parasite interactions. This review provides an overview of the intrinsic properties of anisakid NL and reports the latest detection methods in published literature. First, in order to define the potentially interesting intrinsic properties of anisakid nematodes for their detection, anatomy and compounds involved in host-parasite interactions are summarised. These can be used for various detection approaches, such as in the medical field or for allergen detection in fish products. In addition, fluorescence characteristics and their use as both established and promising candidates for detection methods, especially in the field of optical sensing technologies, are presented. Finally, different detection and identification methods applied by the fish processing industries and by control laboratories are listed. The review intends to highlight trends and provide suggestions for the development of improved detection and identification methods of anisakid NL in fish products.

Immune response of teleost fish to helminth parasite infection

Abstract Fish immune systems have become the subject of several studies due to the growing development of aquaculture and fisheries, and the demand for healthy produce for human consumption. Among the parasites responsible for diseases in fish farming, helminths stand out because they cause infections in farmed fish and decrease food conversion, zootechnical performance and meat quality. In the present review, the components that participate in the innate and adaptive immune responses of teleost fish that have so far been described are presented in order to summarize the defenses that these hosts have recourse to, in combating different groups of helminth parasites.

Presence of Anisakidae in commercial fish species imported into the Belgian food markets: A systematic review and meta-analyses

Anisakidae are marine zoonotic nematodes with most commercial fish species as intermediate hosts. Both public health risks and socio-economic problems are attributed to these larvae. Despite these concerns, the occurrence of Anisakidae in commercial fish species in Belgium remains unknown. Therefore, the main objective of this systematic review was to look into studies assessing the prevalence and intensity (level of infection) of Anisakidae in countries importing fish to the Belgian market. The databases of PubMed, Web of Science, Cordis, Google Scholar, Google, African Journals online and Asia Journals online were searched. Main eligibility criteria were: fish species consumed in Belgium; studies conducted in one of the main importing countries; and the availability of prevalence data. From the original 519 identified studies, 83 were included with data from Spain, Germany, Chile, Denmark, Turkey, France, China, England, Belgium, Norway, Iceland, Senegal and Sweden. Overall results show a widespread occurrence of Anisakidae with a high variability in prevalence between fish species and fishing sea. Cod (Gadus morhua) and Atlantic salmon (Salmo salar), the most consumed fish species in Belgium, have a mean prevalence of 33% and 5% respectively. Of all investigated fishing zones, fish caught in the Northeast Atlantic has the highest rate of infection (68%). Furthermore, higher prevalences were found when looking at the viscera (mean prevalence 59%) compared to the muscle (29%) and with superior techniques such as enzymatic digestion or UV press (46%) compared to candling, the routine method (23%). Farmed fish were found to be the least infected (2%) but were still not Anisakidae free. The widespread presence of Anisakidae and the associated food safety implications indicate the need to further investigate the presence of Anisakidae in fish in the Belgian market.

Nematode infection in liver of the fish Gymnotus inaequilabiatus (Gymnotiformes: Gymnotidae) from the Pantanal Region in Brazil: pathobiology and inflammatory response

BACKGROUND

A survey on endoparasitic helminths from freshwater fishes in the Pantanal Region (Mato Grosso do Sul, Brazil) revealed the occurrence of third-larval stage of the nematode Brevimulticaecum sp. (Heterocheilidae) in most organs of Gymnotus inaequilabiatus (Gymnotidae) also known by the local name tuvira. The aim of the present study was to examine Brevimulticaecum sp.-infected tuvira liver at the ultrastructural level and clarify the nature of granulomas and the cellular elements involved in the immune response to nematode larvae.

METHODS

Thirty-eight adult specimens of tuvira from Porto Morrinho, were acquired in January and March 2016. Infected and uninfected liver tissues were fixed and prepared for histological and ultrastructure investigations.

RESULTS

The prevalence of infection of tuvira liver by the nematode larvae was 95 %, with an intensity of infection ranging from 4 to 343 larvae (mean ± SD: 55.31 ± 73.94 larvae per liver). In livers with high numbers of nematode larvae, almost entire hepatic tissue was occupied by the parasites. Hepatocytes showed slight to mild degenerative changes and accumulation of pigments. Parasite larvae were surrounded by round to oval granulomas, the result of focal host tissue response to the infection. Each granuloma was typically formed by three concentric layers: an outer layer of fibrous connective tissue with thin elongated fibroblasts; a middle layer of mast cells entrapped in a thin fibroblast-connective mesh; and an inner layer of densely packed epithelioid cells, displaying numerous desmosomes between each other. Numerous macrophage aggregates occurred in the granulomas and in the parenchyma.

CONCLUSIONS

Our results in tuvira showed that the larvae were efficiently sequestered within the granulomas, most of the inflammatory components were confined within the thickness of the granuloma, and the parenchyma was relatively free of immune cells and without fibrosis. Presumably this focal encapsulation of the parasites permits uninfected portions of liver to maintain its functions and allows the survival of the host.

Occurrence of zoonotic nematodes Pseudoterranova decipiens, Contracaecum osculatum and Anisakis simplex in cod (Gadus morhua) from the Baltic Sea

Baltic cod Gadus morhua (a total of total 224 specimens) captured east of the island of Bornholm in the southern Baltic Sea were subjected to a parasitological investigation between March 2013 and April 2014. Full artificial digestion of fillets from 188 cod and additional investigation of livers from 36 cod were performed. Cod or seal worm Pseudoterranova decipiens was recorded in musculature (prevalences up to 55% and intensities up to 56 worms per fish) associated with a negative correlation between worm intensity and condition factor. Liver worm Contracaecum osculatum (100% prevalence with intensities up to 320 worms per fish) in liver tissue were recorded but only a slight negative correlation between intensity and condition factor was noted. Seals act as final host for both worm species and the increased occurrence during recent years is associated with the increasing grey seal population in the area. Infection with Anisakis simplex (the herring or whale worm) in Baltic cod was found at a low level corresponding to previous studies.