Cestodes Life Cycle

Cestodes, or tapeworms as they are commonly called, are intestinal parasites that infect meat-eating mammals including such domesticated animals as dogs and cats, as well as humans. Cestodes are called tapeworms because of their flat body shape, which looks like tape. Cestodes vary in size depending on species, but all species of cestode undergo three main life phases: eggs, larvae and adults.

Reproduction

• Tapeworms are hermaphroditic, meaning that they contain both male and female sexual organs. Each segment of a tapeworm's body has male and female sex organs and can fertilize itself, producing eggs.

Egg Production

• Cestode adults attach themselves to the intestinal wall of the host animal using their head section containing several teeth. Once the head has attached itself to the intestinal wall, it begins to grow body segments. Each cestode body segment contains reproductive organs. As the tapeworm increases in size, the segments on the end of the body fall off, releasing the body segments containing eggs into the host's digestive tract.

Egg Release

• Once the body segments are released into the host's digestive system, they are discharged from the host's body in its feces. The body segments are roughly the size of a grain of rice and can move on their own. The body segment eventually dries up and opens, releasing the eggs into the environment.

Larvae

• Once cestode eggs have been released from the body segment, they are often eaten by an animal called an intermediate host. Within this host, the larvae are called cysts. When the intermediate host is eaten by the primary host, the larvae can then develop into adult cestodes. Cestode larvae can cause severe disease within the host animal when they implant into areas other than the intestines. The larvae can infect various organs within the body including the brain, muscles and lungs.

Adult

• Adult cestodes live within the intestines of carnivorous mammals. They do not have a digestive system of their own and instead take in nutrients by absorbing them through their skin from their host's intestines. Adult tapeworms can vary widely in size according to species, but all adult tapeworms have three distinct body segments. These include the head, called the scolex, which secures the tapeworm onto the intestine of the host, a neck portion and several body segments, called proglottids.

Life Span

• Cestodes have different life cycles depending on their species and the life span of their host animal, but some cestodes can live for up to 20 years inside the body of the host animal. When the tapeworm dies, it is deposited in the feces of the host animal like the body segments that are shed throughout the tapeworm's life cycle.