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Lesson Sixteen: Tapeworm Infection (Prevention, Control and Treatment)
Teaching suggestions: Lecture, individual and group work activity, diagrams illustrating the life cycle of tapeworm.
To engage students, pose focus questions like:
Let the teacher orally collects responses from students about the focus questions. The students may suggest what they think of tapeworm infection.
Tapeworms (Cestods) are type of parasitic flatworms that live in the intestines of host organisms, such as humans, cows, pigs, dogs, and cats. The most common tapeworms in humans are fish tapeworm, beef tapeworm, pork tapeworm, and dwarf tapeworm.
Group work
Let the students get organized in small groups and discuss the life cycle of Beef tapeworm, the methods of transmission, prevention, treatment and control.
The teacher should closely supervise the different groups while the group discussion is in progress.
Beef tapeworms usually range between 10 to 15 feet long, but can grow up to 65 feet long in some cases. They most commonly infect cows and humans, but can only reproduce asexually in human hosts. Taenia saginata is a large tapeworm that causes an infection called taeniasis. It is commonly known as the beef tapeworm or cattle tapeworm because it uses cows as intermediate hosts. Humans are the only definitive hosts. Taeniasis occurs worldwide and is relatively common in Africa, Eastern Europe, Latin America and the Philippines.
Fig. 16.1: Life Cycle of Taenia saginata
The life cycle of Taenia saginata starts, when eggs are passed in the feces of an infected human along with a structure called proglottid or a tapeworm segment. They can survive for a few months in the environment. If a cow (the intermediate host) feeds on contaminated vegetation, it ingests mature eggs or gravid proglottids. In the small intestine, the larvae called oncospheres hatch and penetrate the intestinal wall, enter the bloodstream and migrate to muscle tissue (rarely to liver or other organs), where they encyst into cysticerci. The pea-sized cysticerci can survive for years and still be infective when humans eat the meat. If the beef is not cooked properly, cysticerci excyst in the small intestine and develop into adults within two months. Adults attach to the intestinal wall with their scolex using four suckers. The scolex has a pear-shaped and cup-like appearance reaching 1–2 mm in diameter. It is attached to the neck which starts to produce proglottids that make up the flat, long, segmented body also known as strobila. The proglottids mature and grow bigger as they get further from the neck. They are about 16–20 mm long and 5–7 mm wide and each proglottid has its own reproductive organs. They absorb nutrients through their membranes and produce up to 100, 000 eggs per day. Proglottids break off from the tail and move with stool out of the human body. A full-grown Taenia saginata is whitish in colour and has about 1000–2000 proglottids and about six of them detach every day. The eggs usually stay inside the proglottids until they are out in the environment. When the proglottid dries up, it ruptures and releases the eggs. The eggs are embryonated, walnut brown and about 35 micrometers in diameter having a 6-hooked oncosphere inside its thick shell. If the feces land on grazing ground for cattle, a cow might accidentally ingest proglottids or eggs. Taenia saginata can live up to 25 years. It can grow up to 5 meters but in some cases can reach lengths of over 10 meters (coiled in the intestinal tract).
a) Pork Tapeworm
b) Beef Tapeworm
Fig. 16.2: Proglottid of Pork Tapeworm (a) and Beef Tapeworm(b)
Nausea, muscle weakness, weight loss, malnutrition, abdominal pain, passing worm segments along with stool. Migrating proglottids can cause inflammation of the appendix and bile duct. Tapeworms can also move out of the intestines and start infesting other tissues. This is a much more serious condition, causing complications that can require treatment in their own right.
Fever, Cystic lumps or masses, Allergic reactions, Bacterial infections, possible seizures (where brain tissue is involved)
There is effective treatment for tapeworm infection. Since tapeworms prevent the absorption of food, and also medication, the most common course of treatment for tapeworms must attack the worms directly. Your doctor will usually prescribe one of several anthelmintics (parasite-expelling drugs), which are toxic to the worms. These medications kill the adult tapeworms, but do not exterminate larvae. The following methods might be helpful to reduce the spread of tapeworm.
The teacher is expected to give a brief summary of tapeworm infection, life cycle of beef tapeworm, methods of transmission, treatment, prevention and control.