Microhabitat preference of Anisakis simplex in 3 salmonid species: Immunological Implications.

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Third stage larvae of Anisakis simplex nematodes are considered to have a low host-specificity and are able to infect a wide range of fish species. However, the physiological and immunological status of the fish species may affect the fate of the worm following infection. We selected three different salmonid species to investigate the in vivo behavioural difference of experimentally inoculated Anisakis parasite inside these fishes. Rainbow trout (Oncorhynchus mykiss), Baltic salmon (Salmo salar) and brown trout (Salmo trutta) were used in this experiment. Infection success differed between species. Baltic salmon showed a higher number of nematodes successfully established, whereas brown trout and rainbow trout showed a higher natural resistance. Microhabitat results were also different according to the fish species. Anisakis simplex found in brown trout where attached to the digestive tract (stomach, intestine), while the majority of larvae found in rainbow trout were located between the pyloric caeca. In Baltic salmon, nematodes were dispersed and attached to different organs (e.g. spleen, swim bladder) and partially penetrating others (liver, muscles). Encapsulating and inflammatory cellular reactions differed accordingly. Anisakis larvae found both in rainbow trout and brown trout were not fully encapsulated until day 28 post infection but merely partially encapsulated at day 21 post-infection. In contrast, all nematodes larvae retrieved from Baltic salmon were fully encapsulated already at day 21 post infection. Immunohistochemical studies using monoclonal antibodies raised against IgT, IgM, CD8 and MHCII were used to detect the presence of immune cells around the infecting nematodes. None of the three fish species showed positive reactions for IgT and IgM bearing cells in inflammatory tissue in connection with the worms. CD8+ cells were detected in all three species but MHC II bearing cells were only found associated with encapsulated Anisakis in rainbow trout and brown trout, but not in Baltic salmon. In this study we have shown that Anisakis nematodes show a site predilection following infection depending on the host species and the immunological/physiological implications will be discussed.
Original languageEnglish
Publication date2 Nov 2011
Publication statusPublished - 2 Nov 2011
EventDAFINET Workshop - Copenhagen, Denmark
Duration: 2 Nov 20113 Nov 2011


ConferenceDAFINET Workshop

ID: 35249526