In 2003, there was an outbreak of peritonitis in reindeer in the southern and middle part of the Finnish reindeer herding area caused by the filarioid nematode Setaria species. In the province of Oulu, the proportion of reindeer viscera condemned owing to parasitic lesions increased from 4·9 per cent in 2001 to 40·1 in 2003. In 2004, the focus of the outbreak moved approximately 100 km north. A total of 260 adult and pre-adult Setaria species nematodes were collected for morphological and molecular studies. The parasite was indistinguishable in terms of morphology and molecular biology from Setaria tundra. Samples of parasites were also collected from wild cervids. In elk, only a few cases of pre-adult encapsulated S tundra nematodes were detected on the surface of the liver but there was no peritonitis. Two roe deer had S tundra nematodes in their abdomen but no peritonitis. Of 34 wild forest reindeer, 21 had changes associated with S tundra. At meat inspection of the affected reindeer carcases, the changes observed included ascites, green fibrinous deposits, adhesions, and live and dead S tundra nematodes. There were histological lesions of granulomatous peritonitis with lymphoplasmacytic and eosinophilic infiltration. No specific bacterial growth was found. The parasitic infection had no significant effects on the pH or the organoleptic quality of the meat. There was a significant positive correlation between the worm count and the degree of peritonitis (P<0·001) and a negative correlation between the degree of peritonitis and the thickness of the back fat layer (P=0·015).
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