Several tapeworms can infect whitetails, but one of the most visible is the juvenile stage of the canine tapeworm (Taenia hydatigena). This stage, called the bladderworm, appears as a white oval in the liver (as seen in the photo, right) or on membranes within the deer's abdominal cavity.
Deer get infected by consuming plants contaminated with tapeworm eggs. The eggs hatch and burrow through the deer's gut wall, enter blood vessels and emerge within the liver. They move to the surface of the liver and enter the body cavity. Eating tissues from the abdomen of an infected deer can infect a coyote or dog. Deer infected with bladderworms experience minimal ill effects. In addition, bladderworms do not infect humans and do not affect venison quality.
Another species of tapeworm (Echinococcus granulosus), confined mostly to the northern United States and Canada, can be harmful to humans. However, ingesting eggs originating from a dog or coyote, not from consuming deer meat, infects humans. Cysts in deer caused by this tapeworm are harmless to humans but indicate the parasite is present in the region and human infection by other means may be possible.
These slender, white parasites (Setaria yehi, picture right) range from 5 to 10 inches in length. They usually are located in the abdominal cavity, so hunters are most likely to find them as they dress their deer. In some cases, 75 percent of deer may have the parasite, but usually the infection rate is lower. Younger deer are more likely to harbor the parasite than older deer. It does not affect the quality of the venison.
The life cycle of this parasite is not completely understood. It is thought that mosquitoes serve as intermediate hosts and transmit larval stages of the parasites to deer, the final hosts for the adult worms. Like most parasites, Seteria seldom harm the host deer and are of no significance to other animals or humans. Consumption of meat from a deer infected with Seteria is safe.