Relations between histopathology and parasitaemias in Oncorhynchus mykiss infected with Cryptobia salmositica, a pathogenic haemoflagellate

Abstract

One group (n = 50) of juvenile rainbow trout Oncorhynchus mykiss was inoculated intraperitoneally with 2000 (low dose [LD]) and another group (n = 50) with 20 000 (high dose [HD]) Cryptobia salmositica fish -1 . The histopathology was a generalised inflammatory reaction, and lesions were in connective tissues and in the reticulo-endothelial system. In the LD group, the first lesions were observed in the liver, gills and spleen at 2 wk post infection (pi) while in the HD group they were in the liver and gills at 1 wk pi. Endovasculitis and mononuclear cell infiltration were observed at 3 wk pi in the HD group. These were followed by tissue necrosis and extravascular infiltration of parasites at 4 wk pi. The severity of lesions was directly related to parasitaemias in the blood and extravascular location of parasites. In the HD group, the most extensive tissue necrosis was at 4 wk pi and in the LD group it was 6 to 7 wk pi. Necrosis in the vital organs (liver, kidney and depletion of the haematopoeitic tissues) and anaemia were probably in part responsible for mortality of fish during acute disease. Regeneration and replacement of necrotic tissues were seen at 7 to 9 wk pi in the HD group, and it was most noticeable in haematopoietic and reticular tissues. These occurred during the recovery phase of the disease and were associated with significant reduction in blood parasitaemia. KEY WORDS: Cryptobia salmositica · Oncorhynchus mykiss · Histopathology · Parasitaemias Resale or republication not permitted without written consent of the publisherDis Aquat Org 46: [41][42][43][44][45] 2001 MATERIALS AND METHODSTwo groups (n = 50 in each group) of hatchery-raised juvenile rainbow trout (about 6 to 8 cm in length) were maintained in 2 fibre glass tanks at about 8°C for 2 wk before they were experimentally infected with Cryptobia salmositica. The inocula were prepared with blood from an infected rainbow trout and diluted with appropriate volumes of PBS (pH 7.4). The low dose (LD) group was inoculated intraperitoneally (ip) with 2000 parasites fish -1 and the high dose (HD) group with 20 000 parasites fish -1 . At weekly intervals, 4 fish from each group were anesthetised with MS-222 (100 ppm), bled and necropsied. In the first week after infection the parasitaemias in the blood were detected using the haematocrit centrifuge technique and wet mount method (24 microscopic fields examined, 10× objective). In subsequent weeks, the haemocytometer was used to estimate parasitaemias (Woo 1979). For histopathology, samples of visceral organs, skin, eye, brain and gills were fixed in 10% formalin, embedded in paraffin, sectioned into 4 µm thick pieces, and stained with haematoxylin and eosin. Smears of ascites fluid or blood were air dried, fixed in 100% Ethanol and stained with Giemsa's stain. A third group of uninfected fish (controls) was also sampled. RESULTS LD groupThe haematocrit centrifuge technique detected parasites in the blood of all fish at 1 wk post infection (pi).The parasitaemia increased rapidly, p...

A quantitative study of the hepatic eosinophilic granule cells and rodlet cells during the breeding cycle of Ohrid trout, Salmo letnica Kar. (Teloestei, Salmonidae)

“…On the other hand, taking into account our own experience with brown trout [17,21e28], there are no reasons other then species and particular ecosystem that could explain the absence of hepatic EGCs in that trout compared to Ohrid trout. It is known that the occurrence of inflammatory cells is more common in salmonids caught in their natural environment [4] or living under certain pathological conditions or parasite infections [3e6, 8,9,12,13]. In this context, the presence of hepatic EGCs due to their mobilization by external influences cannot be excluded in our case, although in the studied specimens infection with parasites or local liver tissue damage were quite rare events.…”

Amoebic gill disease: sequential pathology in cultured Atlantic salmon, Salmo salar L.

“…Macrophages have shown adherence to the monogenean Gyrodactylus derjavini in vitro resulting in substantial tegument damage (Buchmann & Bresciani 1999). Macrophages are commonly recruited during ectoparasitic insults (Barmanrokh & Woo 2001; Bennett & Bennett 2001; Colquitt, Munday & Daintith 2001). They not only possess phagocytic ability but also contain mediating factors that assist immunoregulation (Secombes & Fletcher 1992; Buchmann 1999; Koppang, Hordvik, Bjerkas, Torvund, Aune, Thevarajan & Endresen 2003).…”

Hypoxemia-induced leptin secretion: a mechanism for the control of food intake in diseased fish

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