What Are the Forms & Stages of Tapeworms?

Tapeworms are a parasitic organism which have given humans and other animals trouble from thousands of years. They can infect or be carried by any class of animal. Some tapeworms can live decades and grow many times longer than the body of its infected host. Tapeworms that can infect humans are the main tapeworms that humans investigate and look to stop. There are several forms of tapeworms and each goes through different stages of life. Having information on tapeworms ensures that if nothing else, we know our enemy.

Pork Tapeworm

• The pork tapeworm is a form of tapeworm also known as taenia solium. It has the ability to infect both pigs and humans and is known to exist in Africa, Asia, South America and pockets within Southern Europe and North America. This tapeworm has four suckers on its head along with two rows of hooks to latch onto the host. This tapeworm has several stages. Eggs are the first stage, where they are released when a host defecates and they are shed out with the defecation. Humans and pigs are infected when they digest food contaminated with this defecation. Once the eggs are ingested, they hatch as "oncospheres," which is a tapeworm embryo. They then migrate from the intestine to other parts of the body such as the brain, liver and striated muscles. Once migrated to these other places, they form into "cysticerci," which is a larval stage. The last stage of the pork tapeworm comes when humans eat undercooked pork containing the "cysticerci" stage of pork tapeworm. These tapeworms can live several years in the small intestine and grow to a length of 2 to 7 meters.

Beef Tapeworm

• The beef tapeworm is also known as taenia saginata and has the ability to infect both humans and cattle. It has four extremely powerful suckers. It is common in parts of Eastern Europe, Africa, Latin America and Southeast Asia. Its most common cause in humans in improper cooking of meat. These tapeworms use cattle as an intermediate host and humans as their definitive host. This tapeworm has a life cycle that differs from some other tapeworms. The adult tapeworm lays eggs in the small intestine of a person, who then passes out these eggs when they defecate. Cows then sometimes come across this defecation while grazing, and the digestive fluids of the cow break through the eggs and release oncospheres (embryo). The oncospheres go through the digestive tract and then enter the circulatory system of the cattle. The embryo enters its larval stage and produces cysticercus, which is a cyst. The adult tapeworm forms when humans eat undercooked or raw meat and their digestive fluids break this cyst, which contains larva. The adult tapeworm then develops, attached to the intestine of its human host, and can grow up to 12 meters long, though only 4 to 10 meters is common.

Dwarf Tapeworm

• Dwarf tapeworm, also known as hymenolepis, is a tapeworm that can infect both humans and rats. The dwarf tapeworm is the most prevalent tapeworm in human hosts. The tapeworm can live anywhere in the world, but is usually found within warmer climates. Unfortunately, there can be very few symptoms to this type of tapeworm until it produces at least 15,000 eggs in each gram of feces it is contained in. The tapeworm is usually passed from human to human due to unsanitary conditions related to fecal matter. The stages of a dwarf tapeworm are more simplistic than others. It needs no intermediary; it can move from one human straight to the next by ingestion of its eggs. Eggs come out through defecation of an infected host. A human can become immediately infected by ingesting food or water that is contaminated. An insect can also carry the eggs, where they will develop into the larval stage cysticerci while on the insect, which may then infect a human or rat. If the human is directly contaminated by either food or water, the tapeworm will go to its larval stage within the intestinal villus of that human host. The larva will then form a scolex, which is a head, that has several hooks which it uses to attach to the host's intestines. At this point, the dwarf tapeworm is in its adult form and can begin passing eggs to infect other hosts.

Fish Tapeworm

• The fish tapeworm, also known as diphyllobothrium, is a genus of tapeworm that can infect several types of mammals and fish and has several places all over the world where it can infect hosts. Humans are most often infected by eating undercooked or raw fish. Evidence of these tapeworms has been found in the remains of humans from 4,000 to 10,000 years ago in South America. The fish tapeworm has several stages of its life cycle. Eggs are passed from a definitive host, where the adult tapeworm resides and end up being eaten by any of a number of freshwater crustaceans. The eggs then hatch into their first larval stage, known as procercoid larvae. The crustacean that consumed the eggs will then be eaten by another host, which is usually a small fresh water fish. Once in the fish, the larvae will enter their second larval phase, known as plerocercoid larvae. This larval stage is the one that is infectious. At this point, the fish tapeworm doesn't pose much of a risk to humans, as it is alive in a small fish that humans would not usually eat. When these small fish are consumed by larger fish, however, therein lies the problems for humans. Humans who ingest undercooked or raw fish (sushi) can then be infected with the plerocercoid larvae, which then progress to immature adult tapeworms, followed by the fully formed mature adult tapeworm. Once in the human host, the fish tapeworm will live in the small intestine for as long as 20 years and grow up to 10 meters in length.