Skip to main content

Deer liver flukes

Liver flukes (Fascioloides magna) are flatworm parasites that may be found in the liver of some deer. Adult flukes are purple-gray in color, flat and oval-shaped. The flukes vary in size from 1.5-3 cm wide to 3-10 cm long. They may look like leeches or blood clots when found in the liver. They are frequently surrounded by a fibrous capsule, in a dark, muddy-appearing fluid.


Eggs from adult flukes pass in the feces of deer. The eggs hatch and the first stage, called miracidia, must enter a snail to continue development. After further development in the snail the next stage, called cercaria, leaves the snail and encyst on vegetation as infective larvae or metacercaria. A deer becomes infected when it eats the vegetation with the larval cyst which then penetrates the intestine of the deer and migrates to the liver where it becomes encapsulated as the adult fluke.


There are no outward signs of the presence of liver flukes. In harvested deer, adult liver flukes may be found when the liver is sliced open. Even though the flukes may cause local damage to the liver, it is rare that the presence of liver flukes significantly affects the health of the deer.


Liver flukes do not significantly affect the wild deer population. Individual deer may have a varying degree of damage to the liver but is in good health, otherwise, they are generally not adversely affected.


Consumption of venison from an infected deer poses no risk to humans. However, the liver of an infected deer should not be consumed as the fluke-damaged areas of the liver can be secondarily infected by bacteria.