A four-year old Husky dog suffering of chronic diarrhea was radiologically diagnosed with megacolon and consequently, partial resection of the colon wall was performed. Histological examination of the colonic wall revealed the presence of Sarcocystis spp. oocysts. Chronic inflammation of colonic mucosa resulted in local amyloidosis, overexpression of Bcl-2 in the goblet cells, which suggested decreased apoptosis and increased mucous cells population in Lieberkühn’s glands. The expression of immunoglobulin A (IgA) was reduced intraepithelially and increased in blood capillaries, periglandulary and in the submucosal stroma consequently to parasitic infection. The colonic mucosa showed plasma cells, eosinophilic, mast cells and lymphocytic infiltrations. The Sarcocystis chronic parasitism may cause colon chronic dilatation due to persistent inflammation of the mucosa, characterized by infiltration of lymphocytes and plasma cells followed by the synthesis of amyloid. The amyloid stored around the Lieberkühn’s glands or in the submucosal stroma can cause autonomic dysfunction in Auerbach's and Meissner's plexuses and autonomic ganglia.

Key words: Amyloidosis, Husky dog, Megacolon, Sarcocystis