DAO 66:245-254 (2005)  -  doi:10.3354/dao066245

Histopathology, ultrastructure and immunohistochemistry of Coregonus lavaretus hearts naturally infected with Ichthyocotylurus erraticus (Trematoda)

Bahram Sayyaf Dezfuli1,*, Luisa Giari1, Edi Simoni1, Andrew Paul Shinn2, Maurizio Manera3, Giampaolo Bosi4

1Department of Biology, University of Ferrara, Via Borsari, 46, 44100 Ferrara, Italy
2Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK
3Department of Alimentary Sciences, University of Teramo, Piazza Aldo Moro 45, 64100 Teramo, Italy
4Department of Veterinary Sciences and Technologies for Food Safety, University of Milan, Via Trentacoste 2, 20134 Milan, Italy
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ABSTRACT: Histopathological, ultrastructural and immunohistochemical investigations were conducted on 26 specimens of powan Coregonus lavaretus (L.) from Loch Lomond (Scotland). The hearts of all 26 powan (15 females and 11 males) investigated harboured metacercariae of the digenean trematode Ichthyocotylurus erraticus (Rudolphi, 1809). The vast majority of metacercariae were located either singly or as an aggregation of white cysts on the surface of the bulbus arteriosus. The intensity of infection ranged from 2 to 200 larvae heart–1, although the number of metacercariae found on male powan did not exceed 13. Histochemically, the parasite cyst wall gave a strong positive reaction with periodic acid schiff (PAS) and a faint positive signal with Azan-Mallory stain. All the metacercariae cysts were embedded in a granulomatous proliferation of heart epicardium tissue, forming a reactive fibroconnective capsule around the parasite. The capsule enclosing the parasite (produced by the host’s reaction to the parasite) measured 13.57 to 90.20 µm (37.43 ± 3.56) in thickness. Within the capsule wall, eosinophilic granular cells (EGCs), granulocytes, melanocytes and, in some instances, partially degenerated or vacuolated epithelioid cells were observed in close proximity to the cyst wall. Pigment-bearing macrophages were scattered throughout the granulomatous host-tissue reaction and as macrophage aggregates (MAs) within the capsules surrounding parasites. Immunohistochemical tests were applied to infected heart sections using 12 different antisera. Nerve fibres immunoreactive to bombesin, substance P (SP), and atrial natriuretic peptide (ANP) antisera were observed in close proximity to the parasite larvae. The presence of a serotonin-like substance was also observed within host immune-cells surrounding trematode cysts. Large cells of the epicardium were found to be immunoreactive to met-enkephalin and vasoactive intestinal peptide (VIP) antisera but not immunoreactive to anti-protein gene-product 9.5 (PGP9.5) sera.


KEY WORDS: Trematode infection · Immunohistochemistry · Neuromodulators · Heart · Coregonus lavaretus


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