Obliterative Endophlebitis in Mute Swans (Cygnus olor) Caused by Trichobilharzia sp. (Digenea: Schistosomatidae) Infection

Abstract

Schistosome infections in mammals cause chronic proliferative vascular lesions associated with the presence of adult parasites in the lumen of mesenteric and portal veins. In birds, however, this has never been reported. In this study, we found obliterative endophlebitis associated with the presence of adult schistosomes (Trichobilharzia sp., probably Trichobilharzia filiformis) as the main pathologic finding in five of eight mute swans (Cygnus olor). On histologic examination, the intestinal and portal veins of these swans showed moderate to severe, diffuse, hyperplastic endophlebitis, characterized by myointimal hyperplasia, often with obliteration of the vascular lumen. In addition, moderate to severe lymphocytic and granulocytic enteritis occurred in all eight swans associated with the presence of schistosome eggs in the intestinal mucosa. Other findings included hepatic and splenic hemosiderosis and high hepatic copper levels. The vascular lesions associated with Trichobilharzia sp. infection may have contributed to the emaciation and death of those mute swans by obstruction of venous return in the intestinal and portal veins.

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…Obliterative endophlebitis caused by adult schistosomes (probably Trichobilharzia filiformis) in the intestinal veins of mute swans (Cygnus olor) has been recorded (216). The intestinal surface showed various stages of villous atrophy with intestinal mucosal lesions, associated with infiltration of the lamina propria of the jejunum and ileum by lymphocytes and plasma cells and by a smaller number of heterophils and eosinophils.…”

“…The intestinal surface showed various stages of villous atrophy with intestinal mucosal lesions, associated with infiltration of the lamina propria of the jejunum and ileum by lymphocytes and plasma cells and by a smaller number of heterophils and eosinophils. Eggs were observed multifocally in the lamina propria of the small and large intestines, and their presence triggered mild to severe granulomatous reactions (216). Eggs laid by the adult worms of Austrobilharzia variglandis in experimentally infected chickens caused edema, cellular infiltration, and hyperplasia of smooth muscle of the muscularis externa of the intestine.…”

Pathology of Whooper Swans (Cygnus cygnus) Infected with H5N1 Avian Influenza Virus in Akita, Japan, in 2008

“…Marked thickening of blood vessel walls associated with schistosome infection has been reported in swans [8,15]. Schistosomes migrate through the viscera and can be found within mesenteric, renal, cloacal, and portal blood vessels [15].…”

“…Schistosomes migrate through the viscera and can be found within mesenteric, renal, cloacal, and portal blood vessels [15]. Van Bolhus et al [15] detected obliterative endophlebitis with schistosomes in the lumens of veins of intestines in five dead mute swans. They speculated that vascular lesions associated with schistosomes infection contributed to the swans' emaciation and death.…”

Schistosomes causing cercarial dermatitis: a mini-review of current trends in systematics and of host specificity and pathogenicity

“…Schistosomes are considered to be highly pathogenic for migratory waterfowl (Graczyk et al 1993), but there are relatively few reports on the clinico-pathological aspects of the infections , van Bolhuis 2004. The general paucity of this information can be explained in part by the ease with which the parasites can be overlooked during gross necropsy due to their small size and occurrence within blood vessels (Wojcinski et al 1987).…”