Immunomodulatory effects of excretory/secretory compounds from Contracaecum osculatum larvae in a zebrafish inflammation model

EFSA Panel on Biological Hazards (BIOHAZ), Koutsoumanis K, Allende A, Alvarez‐Ordóñez A, Bover‐Cid S, Chemaly M, De Cesare A, Herman L, Hilbert F, Lindqvist R, Nauta M, Nonno R, Peixe L, Ru G, Simmons M, Skandamis P, Suffredini E, Buchmann K, Careche M, Levsen A, Mattiucci S, Mladineo I, Santos MJ, Barcia‐Cruz R, Broglia A, Chuzhakina K, Goudjihounde SM, Guerra B, Messens W, Guajardo IM, Bolton D. 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.

Seals, fish, humans and parasites in the Baltic: ecology, evolution and history

Evolutionary and ecological processes affecting the interactions between hosts and parasites in the aquatic environment are at display in the Baltic Sea, a young and ecologically unstable marine ecosystem, where fluctuating abiotic and biotic factors affect the parasitofauna in fish. The dynamic infections of Baltic cod, a subpopulation of the Atlantic cod (Gadus morhua Linnaeus), with third stage anisakid nematode larvae of Pseudoterranova decipiens (Krabbe, 1878) and Contracaecum osculatum (Rudolphi, 1802) have increased following a significant increase of the Baltic grey seal Halichoerus grypus (Fabricius) population in the region. Cod serves as a paratenic host and marine mammals, pinnipeds, are definitive hosts releasing parasite eggs, with faeces, to the marine environment, where embryonation and hatching of the third stage larva take place. The parasite has no obligate intermediate hosts, but various invertebrates, smaller fish and cod act as paratenic hosts transmitting the infection to the seal. Contracaecum osculatum has an impact on the physiological performance of the cod, which optimises transmission of the larva from fish to seal. Thus, a muscle mass decrease of nearly 50% may result from heavy C. osculatum infections, probably amplified by a restricted food availability. The muscle atrophy is likely to reduce the escape reactions of the fish when meeting a foraging seal. In certain regions, where fish and seals are restricted in their migration patterns, such as the semi-enclosed Baltic Sea, the predation may contribute to a severe cod stock depletion. The parasites are zoonotic and represent a human health risk, when consumers ingest insufficiently heat- or freeze-treated infected products. Marked infections of the cod were previously reported during periods with elevated seal populations (late 19th and middle 20th century) and various scenarios for management of risk factors are evaluated in an evolutionary context.

Fabp4 contributes toward regulating inflammatory gene expression and oxidative stress in Ctenopharyngodon idella

Fatty acid-binding protein (Fabp)-4 is a member of the FABP family. Mammalian fabp4 has been demonstrated to involve in inflammation and immunity, whereas the related data of fish fabp4 remain limited. Therefore, we further investigated the effects of fabp4 on immunity in Ctenopharyngodon idella. The fabp4 sequence spanned 405 bp was cloned first, sharing high identity to fabp4 from other fish and mammals. Fabp4 expression was the highest in the adipose tissue, followed by the heart, muscle, and liver. In vivo, lipopolysaccharide (LPS) triggered the expression of fabp4, toll-like receptor (tlr)-22, interleukin (il)-1β, and tumor necrosis factor (tnf)-α in the kidney and spleen. In vitro, exposing C. idella CIK cells to LPS decreased their viability, and the expression of fabp4 was also increased by LPS. However, BMS309403, an inhibitor of FABP4, mitigated these effects. Furthermore, treating the cells with LPS or fabp4 overexpression plasmids resulted in reactive oxygen species (ROS) generation and upregulation of inflammatory genes expression, including tlr22, type-I interferon (ifn-1), interferon regulatory factor (irf)-7, tnfα, il-1β, and interferon-β promoter stimulator 1. These effects were ameliorated by preincubation with BMS309403. Moreover, incubating the cells with glutathione reduced the production of ROS and the expression of inflammatory genes that were evoked by LPS and plasmid treatments. These results showed that fabp4 acts as a pro-inflammatory molecule via elevating ROS levels, providing a novel understanding of the molecular regulation of innate immunity in teleosts.

Anisakidae parasitism activated immune response and induced liver fibrosis in wild anadromous Coilia nasus

Anisakidae nematode larvae is one of the most common parasites in wild anadromous Coilia nasus. This study aims to explore the mechanism of the C. nasus immune response to the parasitism of Anisakid nematode larvae. Results found that Anisakid nematode larvae parasitism caused liver injury as evidenced by histomorphology results as well as high levels of aminotransferase and aspertate aminotransferase. Furthermore, Anisakid nematode larvae parasitism induced an immune response in the host, which was characterized by the elevated populations of macrophages and neutrophils in the liver and head-kidney in the Anisakidae-infected group compared to the noninfected group. The expression of immunoglobulin IgM and IgD in the liver and head-kidney was also increased in the Anisakidae-infected group. The Anisakidae-infected group showed higher activity of antioxidant enzymes catalase and superoxide dismutase, which indicates severe oxidative stress, and increased production of pro-inflammatory cytokines, TNF-α, IL-6 as well as MCP-1 in the liver compared with the noninfected group. As a result of inflammation, livers of hosts in the Anisakidae-infected group showed fibrosis, and elevated expression of associated proteins including α-smooth muscle actin, fibronectin, collagen type I and type III compared with the noninfected group. We demonstrated that Anisakid nematode larvae parasitism results in injury and fibrosis in the liver, and triggers immune cell infiltration and inflammation in the liver and head-kidney of C. nasus. Altogether, the results provide a foundation for building an interaction between parasite and host, and will contribute to C. nasus population and fishery resource protection.

Divya-Herbal-Peya Decoction Harmonizes the Inflammatory Response in Lipopolysaccharide-Induced Zebrafish Model

Background

Divya-Herbal-Peya (DHP) is a plant-based decoction containing fourteen herbs in precise quantities; usually prescribed by the practitioners in Ayurveda to alleviate stress and minimize the exasperating symptoms of recurring infections. Our study aims to provide an experimental validation to the immunomodulatory properties of DHP.

Methods

Physico-chemical analysis of DHP was performed to evaluate the presence of secondary metabolites. The phytochemicals were then identified and quantitated through HPTLC, UHPLC, and GC-MS techniques. To address the scientific rationale behind DHP, lipopolysaccharide (LPS) was intraperitoneally injected in adult zebrafish to develop inflammatory response. Following LPS-induction, abnormality in locomotory behaviour was determined by evaluating the relative swim velocity and the rate of turning in experimental zebrafish. Pathophysiological effects were determined through opercular frequency, behavioural fever, and caudal fin damage. LPS-mediated inflammation was measured of pro-inflammatory cytokines, TNFα, IL-6, and IL-1β expression in the serum of study animals, by RT-PCR.

Results

Our study phytochemically characterized and ascertained the presence of glycyrrhizin, rosmarinic acid, gingerol, cinnamic acid, protocatechuic acid, gallic acid, ellagic acid, piperine and cinnamaldehyde in DHP decoction. LPS induced aberrant locomotory patterns, behavioural fever and caudal fin damage in zebrafish. A significant increase in gene expression levels of pro-inflammatory cytokines, TNFα, IL-6, and IL-1β was also determined. However, these locomotory deviations and behavioural fever were negligible in zebrafish groups pre-administered either with DHP in a dose dependent manner or dexamethasone (DEX). The altered opercular rate, caudal fin damage and elevated transcription levels of pro-inflammatory genes upon LPS-induction were averted in groups pre-treated with DHP and DEX.

Conclusion

DHP prophylactically prevented the LPS-induced abnormal behaviour and inflammation-related pathophysiology in zebrafish. Immunomodulatory properties of DHP may not have therapeutic intervention, but do confer nutraceutical health benefits against mild infections.

Evidence of IgE-Mediated Cross-Reactions between Anisakis simplex and Contracaecum osculatum Proteins

Fish consumers may develop allergic reactions following the ingestion of fish products containing nematode larvae within the genus Anisakis. Sensitized patients may cross-react with proteins from insects, mites and mollusks, leading to allergic reactions even in the absence of the offending food. Potential cross-reactivity in Anisakis-allergic patients with larval proteins from other zoonotic parasites present in freshwater and sea fish should be investigated due to an increasing occurrence in certain fish stocks, particularly Contracaecum osculatum. In this work, we evaluated IgE-cross reactions by in vivo (skin prick tests with parasites extracts) and in vitro methods (IgE-ELISA and IgE-immunoblot). In vivo skin prick tests (SPT) proved the reactivity of Anisakis-sensitized patients when exposed to C. osculatum antigens. Sera from Anisakis-sensitized patients confirmed the reaction with somatic antigens (SA) and excretory/secretory proteins (ES) from C. osculatum. Only anecdotal responses were obtained from other freshwater worm parasites. Consequently, it is suggested that Anisakis-sensitized humans, especially patients with high levels of specific anti-Anisakis antibodies, may react to C. osculatum proteins, possibly due to IgE-mediated cross-reactivity.

Systems Pharmacology and Verification of ShenFuHuang Formula in Zebrafish Model Reveal Multi-Scale Treatment Strategy for Septic Syndrome in COVID-19

The outbreak of coronavirus disease 2019 (COVID-19) has affected millions of people worldwide. Critically ill COVID-19 patients develop viral septic syndrome, including inflammatory damage, immune dysfunction, and coagulation disorder. In this study, we investigated ShenFuHuang formula (SFH), a traditional Chinese medicine, which has been widely used as complementary therapy for clinical treatment of COVID-19 in Wuhan, to understand its pharmacological properties. Results of systems pharmacology identified 49 active compounds of SFH and their 69 potential targets, including GSK3β, ESR1, PPARG, PTGS2, AKR1B10, and MAPK14. Network analysis illustrated that the targets of SFH may be involved in viral disease, bacterial infection/mycosis, and metabolic disease. Moreover, signaling pathway analysis showed that Toll-like receptors, MAPK, PPAR, VEGF, NOD-like receptor, and NF-kappa B signaling pathways are highly connected with the potential targets of SFH. We further employed multiple zebrafish models to confirm the pharmacological effects of SFH. Results showed that SFH treatment significantly inhibited the inflammatory damage by reducing the generation of neutrophils in Poly (I:C)-induced viral infection model. Moreover, SFH treatment could improve the phagocytosis of macrophages and enhance the expression of immune genes in an immune deficiency model. Furthermore, SFH treatment exhibited promising anti-thrombosis effect in a thrombus model. This study provided additional evidence of SFH formula for treating COVID-19 patients with septic syndrome using multiple-scale estimation.

Contracaecum osculatum (sensu lato) infection of Gadus morhua in the Baltic Sea: inter- and intraspecific interactions

The subpopulation of Atlantic cod, Gadus morhua, in the eastern part of the Baltic Sea has experienced a significant increase in infections with anisakid nematode larvae of the species Contracaecum osculatum sensu lato (s.l.) since the year 2000. The life cycle of the parasite includes seals and especially the grey seal, Halichoerus grypus, as final hosts, carrying the adult nematodes in the stomach, crustaceans (copepods, amphipods) as first intermediate hosts and various fish species (clupeids, sandeel) including cod as second intermediate/paratenic hosts. Cod with a body length below 28 cm are generally non-infected but experience increasing infection levels when they switch to a piscine diet (infected intermediate/paratenic hosts). We present an overall frequency distribution analysis of worms in 166 cod (body length 30-49 cm) collected in the spawning area over the last 5 years. It shows a fit to the negative binomial distribution, a prevalence of infection of 89.8%, a mean intensity of 29.3 parasites per fish (range 1-377) and a variance/mean ratio of 59.2 (≫1), indicating overdispersion. We present measurements of the adult Contracaecum osculatum (s.l.) specimens in the seal stomach and show that the parasites reach a maximum length of 6.6 cm (females) and 5.8 cm (males). L3s in sprat have a total length from 1to 11 mm whereas the larvae in cod liver are 3-27 mm. A decreasing mean worm length associated with high worm densities in cod (number of nematodes per liver) was recorded. Possible explanations might include timing of feeding on infected intermediate/paratenic hosts, intraspecific competition (crowding) between larvae in cod and host responses (indicated by a significant antibody production in cod against C. osculatum (s.l.) antigens). A significant negative correlation between infection intensity and muscle mass of cod was found, suggesting parasite-induced down-regulation of growth factors in cod.

The excretory/secretory products of fifth-stage larval Angiostrongylus cantonensis induces autophagy via the Sonic hedgehog pathway in mouse brain astrocytes

Angiostrongyliasis is induced by the nematode Angiostrongylus cantonensis and leads to eosinophilic meningitis and meningoencephalitis in humans. Excretory-secretory products (ESPs) are important investigation targets for studying the relationship between hosts and nematodes. These products assist worms in penetrating the blood-brain barrier and avoiding the host immune response. Autophagy is a catabolic process that is responsible for digesting cytoplasmic organelles, proteins, and lipids and removing them through lysosomes. This process is essential to cell survival and homeostasis during nutritional deficiency, cell injury and stress. In this study, we investigated autophagy induction upon treatment with the ESPs of the fifth-stage larvae (L5) of A. cantonensis and observed the relationship between autophagy and the Shh pathway. First, the results showed that A. cantonensis infection induced blood-brain barrier dysfunction and pathological changes in the brain. Moreover, A. cantonensis L5 ESPs stimulated autophagosome formation and the expression of autophagy molecules, such as LC3B, Beclin, and p62. The data showed that upon ESPs treatment, rapamycin elevated cell viability through the activation of the autophagy mechanism in astrocytes. Finally, we found that ESPs induced the activation of the Sonic hedgehog (Shh) signaling pathway and that the expression of autophagy molecules was increased through the Shh signaling pathway. Collectively, these results suggest that A. cantonensis L5 ESPs stimulate autophagy through the Shh signaling pathway and that autophagy has a protective effect in astrocytes.

In helminthes, Excretory-secretory products (ESPs) contains a wide range of molecules, including proteins, lipids, glycans, and nucleic acids, that assist in the penetration of host defensive barriers, reduction of oxidative stress, and avoid the host immune attack. It has been known as a key factor for parasite development, including feeding, invasion and molting. Therefore, ESPs is a valuable target for the investigation of the host-parasite relationships. However, only a few researches about the function of Angiostrongyliasis cantonensis ESPs have been verified to date. Angiostrongyliasis cantonensis, a blood-feeding nematode, and it is an important causative agent of eosinophilic meningitis and meningoencephalitis in human. Recent our studies have demonstrated that the A. cantonensis ESPs can induce oxidative stress, apoptosis, and immune response. In this study, we will use a mouse astrocytes as a model to investigate the signaling mechanisms of autophagy induction by ESPs treatment. First, the Microarray, Western blotting, and Transmission electron microscopy data demonstrated that A. cantonensis ESPs can induce autophagy generation in astrocytes. Next, ESPs-induced autophagy was activated via Sonic hedgehog (Shh) signaling, and it has a protective potential for astrocytes. These finding will provide new insights into the mechanisms and effects of the A. cantonensis ESPs.

Differences in Gene Expression Profiles of Seven Target Proteins in Third-Stage Larvae of Anisakis simplex (Sensu Stricto) by Sites of Infection in Blue Whiting (Micromesistius poutassou)

The third-stage larvae of the parasitic nematode genus Anisakis tend to encapsulate in different tissues including the musculature of fish. Host tissue penetration and degradation involve both mechanic processes and the production of proteins encoded by an array of genes. Investigating larval gene profiles during the fish infection has relevance in understanding biological traits in the parasite’s adaptive ability to cope with the fish hosts’ defense responses. The present study aimed to investigate the gene expression levels of some proteins in L3 of A. simplex (s.s.) infecting different tissues of blue whiting Micromesistius poutassou, a common fish host of the parasite in the NE Atlantic. The following genes encoding for Anisakis spp. proteins were studied: Kunitz-type trypsin inhibitor (TI), hemoglobin (hb), glycoprotein (GP), trehalase (treh), zinc metallopeptidase 13 (nas 13), ubiquitin-protein ligase (hyd) and sideroflexin 2 (sfxn 2). Significant differences in gene transcripts (by quantitative real-time PCR, qPCR) were observed in larvae located in various tissues of the fish host, with respect to the control. ANOVA analysis showed that relative gene expression levels of the seven target genes in the larvae are linked to the infection site in the fish host. Genes encoding some of the target proteins seem to be involved in the host tissue migration and survival of the parasite in the hostile target tissues of the fish host.

Local immune depression in Baltic cod (Gadus morhua) liver infected with Contracaecum osculatum

Third-stage larvae of the anisakid nematode Contracaecum osculatum infecting cod (Gadus morhua) liver elicit a host immune response involving both innate and adaptive factors, but the reactions differ between liver and spleen. Inflammatory reactions occur in both liver and spleen, but a series of immune effector genes are downregulated in liver infected with nematodes whereas these genes in spleen from the same fish are upregulated. A series of novel primer and probe sets targeting cod immune responses were developed and applied in a real-time quantitative polymerase chain reaction set-up to measure the expression of immune-relevant genes in liver and spleen of infected and uninfected cod. In infected liver, 12 of 23 genes were regulated. Genes encoding cytokines associated with inflammatory reactions (IL-1β, IL-6, IL-8) were significantly upregulated, whereas genes encoding effector molecules, assisting the elimination of pathogens, C-reactive protein (CRP)-PII, hepcidin, lysozyme G1, lysozyme G2, C3 and IgDm, were significantly downregulated. The number of downregulated genes increased with the parasite burden. In spleen, 14 of 23 immune genes showed significant regulation and nine of these were upregulated, including genes encoding CRPI, CRPII, C3, hepcidin and transferrin. The general gene expression level was higher in spleen compared to liver, and although inflammation was induced in nematode-infected liver, the effector molecule genes were depressed, which suggests a worm-induced immune suppression locally in the liver.

Transcriptomic analysis of Baltic cod (Gadus morhua) liver infected with Contracaecum osculatum third stage larvae indicates parasitic effects on growth and immune response

High infection levels due to third-stage larvae of the anisakid nematode Contracaecum osculatum have been documented in cod from the eastern part of the Baltic sea during the latest decades. The nematode larvae mainly infect the liver of Baltic cod and prevalence of infection has reached 100% with a mean intensity up to 80 parasites per host in certain areas and size classes. Low condition factors of the cod have been observed concomitant with the rise in parasite abundance suggesting a parasitic effect on growth parameters. To investigate any association between parasite infection and physiological status of the host we performed a comparative transcriptomic analysis of liver obtained from C. osculatum infected and non-infected cod. A total of 47,025 predicted gene models showed expression in cod liver and sequences corresponding to 2084 (4.43%) unigenes were differentially expressed in infected liver when compared to non-infected liver. Of the differentially expressed unigenes (DEGs) 1240 unigenes were up-regulated while 844 unigenes were down-regulated. The Gene Ontology (GO) enrichment analysis showed that 1304 DEGs were represented in cellular process and single-organism process, cell and cell part, binding and catalytic activity. As determined by the Kyoto Encyclopedia of Gene and Genomes (KEGG) Pathways analysis, 454 DEGs were involved in 138 pathways. Ninety-seven genes were related to metabolic pathways including carbohydrate, lipid, and amino acid metabolism. Thirteen regulated genes were playing a role in immune response such as Toll-like receptor signaling, NOD-like receptor signaling, RIG-I-like receptor signalling and thirty-six genes were associated with growth processes. This indicates that the nematode infection in Baltic cod may affect on molecular mechanisms involving metabolism, immune function and growth.

Gene expression profiles of antigenic proteins of third stage larvae of the zoonotic nematode Anisakis pegreffii in response to temperature conditions

Anisakis pegreffii, a recognised etiological agent of human anisakiasis, is a parasite of homeothermic hosts at the adult stage and of ectothermic hosts at the third larval stage. Among distinct factors, temperature appears to be crucial in affecting parasite hatching, moulting and to modulate parasite-host interaction. In the present study, we investigated the gene transcripts of proteins having an antigenic role among excretory secretory products (ESPs) (i.e., a Kunitz-type trypsin inhibitor, A.peg-1; a glycoprotein, A.peg-7; and the myoglobin, A.peg-13) after 24 h, in A. pegreffii larvae maintained in vitro, under controlled temperature conditions. Temperatures were 37 °C and 20 °C, resembling respectively homeothermic and ectothermic hosts conditions, and 7 °C, the cold stress condition post mortem of the fish host. Primers of genes coding for these ESPs to be used in quantitative real-time PCR were newly designed, and qRT-PCR conditions developed. Expression profiles of the genes A.peg-1 and A.peg-13 were significantly up-regulated at 20 °C and 37 °C, with respect to the control (larvae kept at 2 °C for 24 h). Conversely, transcript profiles of A.peg-7 did not significantly change among the chosen temperature conditions. In accordance with the observed transcript profiles, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed the presence of the three target ESPs at 37 °C, while only A.peg-13 was observed at 7 °C. The results suggest that temperature conditions do regulate the gene expression profiles of A.peg-1 and A.peg-13 in A. pegreffii larvae. However, regulation of the glycoprotein A.peg-7 is likely to be related to other factors such as the host's immune response.

Transcriptome and metabolome analyses of Coilia nasus in response to Anisakidae parasite infection

Parasites from the family Anisakidae are capable of infecting a range of marine fish species worldwide. Coilia nasus, which usually feeds and overwinters in coastal waters and spawns in freshwater, is highly susceptible to infection by Anisakidae. In this study, we used scanning electron microscopes to show that C. nasus infected by Anisakidae exhibited damage and fibrosis of the liver tissue. To better understand host immune reaction and metabolic changes to Anisakidae infection, we used a combination of transcriptomic and metabolomic method to characterize the key genes and metabolites, and the signaling pathway regulation of C. nasus infected by Anisakidae. We generated 62,604 unigenes from liver tissue and identified 391 compounds from serum. Of these, Anisakidae infection resulted in significant up-regulation of 545 genes and 28 metabolites, and significant down-regulation of 416 genes and 37 metabolites. Seventy-four of the 961 differentially expressed genes were linked to immune response, and 1, 2-Diacylglycerol, an important immune-related metabolite, was significantly up-regulated after infection. Our results show activation of antigen processing and presentation, initiation of the T cell receptor signaling pathway, disruption of the TCA cycle, and changes to the amino acid and Glycerolipid metabolisms, which indicate perturbations to the host immune system and metabolism following infection. This is the first study describing the immune responses and metabolic changes in C. nasus to Anisakidae infection, and thus improves our understanding of the interaction mechanisms between C. nasus and Anisakidae. Our findings will be useful for future research on the population ecology of C. nasus.

Comparative susceptibilities and immune reactions of wild and cultured populations of Caspian trout Salmo trutta caspius to VHSV

Caspian trout Salmo trutta caspius is an endangered subspecies of brown trout Salmo trutta which is native to the Caspian Sea. Restocking programmes have been established, but recent introduction of the rhabdovirus viral haemorrhagic septicaemia virus (VHSV) into Iranian rainbow trout farms connected to waterbodies supporting wild Caspian trout may represent an additional threat to the declining stock. The susceptibility of wild and cultured populations of this endemic subspecies was demonstrated by performing controlled VHSV infection experiments (both by bath and injection challenges). Subsequently, VHSV infection in exposed fish was confirmed (CPE and quantitative PCR), virus levels were measured, and regulation of immune genes in exposed fish was investigated with a focus on the genes encoding IL-8, IFNγ, TGFβ, TNFα, SAA, C3-4, CD8α, IgM, MHC I, MHC II, iNOS and IGF-1. The presence of IgM-, CD8α- and MHC II-positive cells in host organs was visualized by immunohistochemistry. Both wild and cultured trout strains proved to be VHSV-susceptible following experimental challenge, but the mortality curves and associated regulation of immune-related genes differed between the 2 trout types. Implications of the results for future management of Caspian trout populations are discussed.

Extrusion of Contracaecum osculatum nematode larvae from the liver of cod (Gadus morhua)

Baltic cod livers have during recent years been found increasingly and heavily infected with third-stage larvae of Contracaecum osculatum. The infections are associated with an increasing population of grey seals which are final hosts for the parasite. Heavy worm burdens challenge utilization and safety of the fish liver products, and technological solutions for removal of worms are highly needed. We investigated the attachment of the worm larvae in liver tissue by use of histochemical techniques and found that the cod host encapsulates the worm larvae in layers of host cells (macrophages, fibroblasts) supported by enclosures of collagen and calcium. A series of incubation techniques, applying compounds targeting molecules in the capsule, were then tested for their effect to induce worm escape/release reactions. Full digestion solutions comprising pepsin, NaCl, HCl and water induced a fast escape of more than 60% of the worm larvae within 20 min and gave full release within 65 min but the liver tissue became highly dispersed. HCl alone, in concentrations of 48 and 72 mM, triggered a corresponding release of worm larvae with minor effect on liver integrity. A lower HCl concentration of 24 mM resulted in 80% release within 35 min. Water and physiological saline had no effect on worm release, and 1% pepsin in water elicited merely a weak escape reaction. In addition to the direct effect of acid on worm behaviour it is hypothesised that the acid effect on calcium carbonate in the encapsulation, with subsequent release of reaction products, may contribute to activation of C. osculatum larvae and induce escape reactions. Short-term pretreatment of infected cod liver and possibly other infected fish products, using low acid concentrations is suggested as part of a technological solution for worm clearance as low acid concentrations had limited macroscopic effect on liver integrity within 35 min.