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Ichthyobodosis (Costiosis, Ichthyobodo necator Complex)
Pathogenesis
Ichthyobodo exists in two forms:
The detached, mobile (free-living) form: has two or four flagella, all of which are difficult to see in actively moving parasites, measures 10–15 μm in length and is usually oval or kidney shaped
The attached form: While the parasite feeds on the fish, it is curled into a pyriform shape and is attached to and penetrates the epithelium
Clinical signs:
Ichthyobodo can cause considerable mortalities, sometimes with little obvious pathology, but other times with spongiosis and epithelial sloughing. Tissue irritation also leads to epithelial hyperplasia and increased mucus production, giving fish a bluish cast (slime)
History/Physical Examination:
typical signs include pruritus (“ flashing”), dyspnea, “ cloudy ” skin, secondary microbial infections; drop in temperature; bluish or whitish film on body
Diagnosis
Histopathology
Histologically, there is a reduction of mucous cells early in the infection, while lamellar hyperplasia occurs in the recovery phase. Other lesions include erosive and ulcerative dermatitis
Gill lesions include exhaustion of the goblet cells, diffuse hyperplasia, sometimes with characteristic cavitation, and degeneration of epithelial and mucous cells, fusion of adjacent lamellae and cell sloughing
Damage to sub-surface cells show dramatic degeneration of the cytoplasm, although the nucleus usually remains intact
In the recovery phase, large numbers of eosinophilic granular cells may be seen within the lamellae
Treatment
Formalin bath
Formalin prolonged immersion
Potassium permanganate prolonged immersion
Raise temperature >30 °C (86° F)
Salt bath (freshwater only)
Secnidazole oral
Triclabendazole
Metronidazole oral