fluke, Distoma polyoon von Linstow 1887

Nonindigenous Occurrences: Leyogonimus polyoon is established in the upper Mississippi River and Wolf River systems having caused mass avian mortality events in Lake Winnibigoshish, Minnesota (Sites 24, 936, 939) in 2007 and 2008 (Lawrence et al. 2009) and in Wisconsin in 1996, 1997, and 2007 (Cole 2001; Dierauf 2007). This parasite’s first collection in the New World was from coots in Shawano Lake, Wisconsin in 1996 (Cole 2001). It was not identified until the following year, when it was also found in faucet snails in Lake Butte des Morts and Lake Winneconne (Cole 2001). By 2007, this species had spread in the Great Lakes basin (but not below ordinary mean high water or directly connecting waters) to give rise to outbreaks in Lake Onalaska, Wisconsin (Arrowhead Island, Navigation Pool 7; Dierauf 2007)  and Lake Winnibigoshish, Minnesota (Lawrence et al. 2009).

In its native range, the definitive hosts of L. polyoon are the common moorhen (Gallinula chloropus) and Eurasian coot (Fulica atra), found in both the duodenum and intestine of host birds (Okulewicz et al. 2010). In North America, infection is so far limited to the American coot (Fulica americana; Cole 2001). A conservative estimate of over 40,000 of these trematodes have been found within the intestine of a single bird (Cole and Franson 2006), while in another case, analysis of fewer than 25 coot yielded L. polyoon counts of 80 to 4,540 (Lawrence et al. 2009).

Potential pathways of introduction: Hitch-hiking or fouling of recreational gear, boats, trailers, or mobile fauna entering the Great Lakes from surrounding region

Introduction of L. polyoon to North America is likely to have resulted from the introduction of the faucet snail (Ross 2008). Spread to the Great Lakes could occur via migration of infected birds from Wisconsin or Minnesota to the Great Lakes and subsequent transmission of the parasite to previously uninfected faucet snails. Rebecca Cole (personal communication) notes that this parasite likely infects other gallinules, which also would also contribute to its spread potential.

Infected faucet snails attached to boats or other equipment could also transport this parasite (Lawrence et al. 2009).

Leyogonimus polyoon has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: Low).

In North America, L. polyoon is predicted to be geographically restricted to the Great Lakes basin, though it is not yet found below ordinary mean high water or directly connecting waters (Cole and Franson 2006). Establishment in lakes in Minnesota and Wisconsin over the course of a decade suggests that L. polyoon could also spread to and overwinter in the Great Lakes, but its environmental parameters are uncharacterized. One of its intermediate hosts, the faucet snail, is a non-indigenous aquatic snail from Eurasia that was introduced into Lake Michigan in 1871; this snail has spread to the Great Lakes region, as well as to the mid-Atlantic states and Montana. The trematode’s additional required hosts, aquatic insects and American coots, are also widespread in the Great Lakes (Cole 2001). Shallow, protected shorelines where birds feed or rest along the Great Lakes may offer more of an opportunity for L. polyoon eggs to hatch from released feces and infect B. tentaculata (Lawrence et al. 2009).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic

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.

There are no known regulations for this species.

Note: Check federal, state, and local regulations for the most up-to-date information.

Control:

Biological
There are no known biological control methods for this species.

Physical
As is typical of avian transmitted pathogens, management and control of L. polyoon is expected to be limited by the migrant nature of the host, difficulty in diagnosis, and lack of adequate resources (McLean 2003). Proposed control efforts focus on interruption of the complex lifestyle of this flatworm. It has been suggested that harvesting the weeds where coots feed (and accidentally ingest caddis fly larvae) may be one mechanism for control (Seely 2009). However, eliminating this nursery habitat is a controversial solution, and other proposed control activities recommend focus on the faucet snail (e.g., reducing overwintering snail populations with molluscicides in early spring) (Cole and Franson 2006). Such a solution may also stem the spread of two other pathogenic trematodes carried by the faucet snail, Sphaeridiotrema globulus and Cyathocotyle bushiensis, first reported to cause waterfowl mortality in North America in the early 1900s and subsequently carried into the Mississippi River system (Cole and Franson 2006). Transportation of boats or other equipment from localities where the faucet snail is present should proceed with caution so as to reduce the risk not only of spreading the snail but also of transporting this parasite (Lawrence et al. 2009).

Freezing infected snails can be a viable control method for the host species, with 100% mortality after 30 mins in dry conditions and 80% mortality in wet conditions (LaFond et al. 2021).

Chemical
There are no known chemical control methods for this species.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.