(Other names: American liver fluke, giant liver fluke)
Deer liver infected with flukes. The encapsulated areas are where the fluke has encysted, or become enclosed in a cyst.
Description
Deer liver flukes (Fascioloides magna) are parasitic worms found in deer livers. Their color tends to be a purplish-gray, and they resemble the texture of a blood clot. These parasites can be as large as 3 inches long and more than an inch wide.
Transmission
Liver flukes have a complex life cycle. While in a deer, flukes are present within fibrous capsules in the liver, where they produce eggs. Deer then pass fluke eggs when they defecate. When these eggs hatch in a wet environment, such as slow-moving streams, ditches, and wetlands, they become free-living miracidia, which is the fluke’s free-living larval stage. The miracidia penetrate aquatic gastropods (aquatic snails), where they continue to grow. Eventually, the miracidia become enclosed and deposit on aquatic vegetation. Deer can then become infected when they ingest aquatic vegetation. Deer are the definitive host for liver flukes, meaning that the fluke can reproduce inside of a deer. Deer liver flukes rarely kill deer.
Clinical Signs
Although liver flukes do not often kill deer, they still produce postmortem clinical signs of infection. When slicing into a deer liver infected with flukes, the meat of the liver will have encapsulated dark spots (see photo).
Wildlife Management Implications
Deer liver flukes do not usually harm deer, but it is still important to report them for the purpose of state disease monitoring using our online sick or dead wildlife reporting tool.
If you suspect livestock are becoming infected with deer liver fluke, please contact the Indiana Board of Animal Health.
Human Health
While deer livers infected with flukes are unsightly and unpalatable compared to uninfected livers, eating deer flukes is not known to negatively affect human health. However, many other types of liver flukes do cause infection in humans. It is always safe to avoid eating any type of liver fluke.
Additional Sources
PennVet Wildlife Futures Program
"Is This Safe To Eat?" (2006). USDA National Wildlife Research Center - Staff Publications. 427. https://digitalcommons.unl.edu/icwdm_usdanwrc/427
Olsen, O. W. (1949). White-tailed deer as a reservoir host of the large American liver fluke. Veterinary medicine, 44(1), 26-30.
Pybus, M. J. (2001). Liver flukes. Parasitic diseases of wild mammals, 121-149.