Tapeworms, which fall into the invertebrate class Cestoda, are flat, parasitic species that occur all over the world. Not all species are pathogenic to humans, but the two most common in human infections are Tenia solium, or the pork tapeworm, and Tenia saginata, or the beef tapeworm. While there are some small differences between species, for the most part, members of the genus Tenia share many common traits.
Size and Shape
According to the South Carolina School of Medicine, Tenia saginata can grow to be quite long---up to 6 meters, or nearly 20 feet. Pork tapeworms are slightly smaller, and both are flattened and relatively slender of body---typically around half an inch wide. Both species have a series of suckers---solium also has hooks---near the head, which allow them to attach to the lining of the host's intestine. Further, tapeworms are segmented and each segment is equipped with a uterus, meaning that if the tapeworm breaks, individual segments remain viable and capable of laying eggs.
Life Cycle
According to the Centers for Disease Control and Prevention, the tapeworm life cycle begins when an infected host passes the eggs of tapeworms together with stool. A new host is then infected with the eggs when it grazes, in the case of cattle or pigs, or eats contaminated vegetable matter or meat, in the case of humans. The eggs pass into the intestine of the newly infected host and hatch. Once hatched, they attach to the wall of the host intestine, and eventually migrate into the muscles.
Pathogenic Characteristics
Tapeworms are highly infectious, with infections resulting in a wide variety of symptoms. According to the Medical News Today website, signs of human tapeworm infection include abdominal pain, nausea and vomiting. Because tapeworms depend upon their hosts for nutrition, symptoms of malabsorption and malnutrition are also common to tapeworm infections. In fact, during certain periods of history and in some cultures, tapeworm eggs were used as dietary aids, and were purposefully swallowed in order to assist with weight loss. It's possible for unchecked tapeworm infection to result in migration of parasites to the human brain, which can lead to altered consciousness, dizziness, seizures and convulsions.
Drug Susceptibility
Both species of Tenia are susceptible to various anti-parasitic drugs, including albendazole and the more frequently used praziquantel, according to the CDC, which notes that treatment is very effective at eradicating infection, though diagnosis---and therefore treatment---is not possible until an infection has been established for at least three months, since it takes some time for eggs, which are used as the diagnostic tool for infection, to pass in the stool.
