Leyogonimus polyoon has the potential for high environmental impact if introduced to the Great Lakes. Birds infested with L. polyoon develop severe enteritis (intestinal trematodiasis), characterized by gross lesions, thickening of intestinal wall, a firm and distended duodenum and jejunum, and fibrinous to caseous cores of necrotic debris in the intestines that occlude the lumen (Cole and Franson 2006). Symptoms are similar to those of avian cholera (Seely 2009), including body weight loss, weakness, lethargy, and death as a result of hemorrhaging, anemia, blood loss, and shock (Cole and Franson 2006, Lawrence et al. 2009). Heavily infected birds may experience difficulty diving and flying (Lawrence et al. 2009).
Previous gallinule infestation in the parasite’s native range was limited to Eurasian coot and common moorhen, but through its introduction to North America, L. polyoon was able to infect the native American coot and likely infects other gallinules (Rebecca Cole personal communication; Cole and Franson 2006). Initial die offs of over 1,000 American coot in Shawano Lake, located at the headwaters of the Wolf River, WI in 1996 went undiagnosed until a mass mortality event was observed the following fall (Seely 1999). In 1997, infestation of L. polyoon killed over 11,000 coot (Cole and Friend 1999; Cole and Franson 2006). By 2002, this parasite had caused the death of more than 24,000 birds in northwestern Wisconsin (Cole 2001). From late October through mid-November 2007, 200 coot on Lake Winnibigoshish in north central Minnesota were killed by fluke infestation, including that by L. polyoon (Lawrence et al. 2009). Population level effects of these mortality events are unknown.
Current research on the potential for socio-economic impacts to result from Leyogonimus polyoon if introduced to the Great Lakes is inadequate to support proper assessment.
Mass bird mortality at sites infested with L. polyoon may temporarily impact recreational use and diminish the aesthetic value of those areas, but the extent to which has not been studied.
There is little or no evidence to support that Leyogonimus polyoon has the potential for significant beneficial effects if introduced to the Great Lakes.
Leyogonimus polyoon has not been reported to act as a biological control agent, have commercial, recreational, or medical value, increase water quality, nor have any positive ecological impacts.