Tapeworms (Cestodes)

27.7 Tapeworms (Cestodes)

Tapeworms are long, flat, white worms that live in the small intestine. These worms have a segmented body, and a head with a sucking mouth part.

Tapeworms require two different animals to complete their life cycle. The immature tapeworm makes a cyst in an “intermediate host” and can cause illness in animals and people. The adult tapeworm lives in a “definitive host” and does not usually cause serious illness.

General Lifecycle: See pages 338, 339 and 340.

1. A definitive host animal eats the cyst often by eating the meat of an infected intermediate host. In the intestines, the cyst (immature tapeworm) leaves its shell and develops into an adult. The adult consists of many segments each containing eggs. The segments break off, pass out in the feces, and release eggs.

1. The eggs are eaten by an intermediate host and hatch into larvae. The larvae move throughout the body of the intermediate host and form cysts.

Diagnosis:

 Symptoms: In the definitive host, there are few clinical symptoms, except possibly some diarrhea. However, tapeworm segments, resembling rice, may be seen in the feces.

 In the intermediate host, the cysts can cause various symptoms depending upon their location, but are difficult to diagnose except by special laboratory tests.

 Laboratory: If the segments from an infected definitive host are squashed, then the tapeworm eggs can be seen with a microscope. Diagnosing cysts in an infected intermediate host requires specialized tests.

Treatment:

 In livestock, treatment of the cysts is usually difficult or unfeasible. In people, some cysts can be removed surgically or treated with special medicines.

 Treatment of the adult tapeworm breaks the cycle of the tapeworm.

Control:

 In general, preventing the definitive host from eating the raw meat of intermediate host can help break the cycle of most tapeworms.

 Use of latrines by humans, and cooking pig meat very well before eating it can help control the pig-human tapeworm.

Specific examples of tapeworms -
Their definitive hosts, and intermediate hosts
Humans
As definitive hosts, humans can have digestive upsets from the pork tapeworm “Taenia solium” and beef tapeworm “Taenia saginata.”
As intermediate hosts, humans can be seriously ill by the cysts of “Taenia solium,” and
“Echinococcus granulosa.”
Cattle and Buffalo
As definitive hosts, cattle and buffalo are not usually affected by adult tapeworms.
As intermediate hosts, cattle can be sick from the cysts of Echinococcus. They are may have cysts from “Taenia saginata” which can ruin their meat.
Sheep and Goats
As definitive hosts, young sheep and goats can be affected by the adult tapeworm Monezia. Adult sheep and goats are not usually affected by adult tapeworms.
As intermediate definitive hosts, sheep and goats have cysts from the species “Taenia” and “Echinococcus” resulting in “circling disease” or “Gid”
Pigs
As definitive hosts, pigs are not usually affected by adult tapeworms.
As intermediate hosts, pigs have cysts of Echinococcus granulosa and Taenia solium which may ruin the meat, but the pigs do not get sick.
Dogs
As definitive hosts, dogs may be infected by the adults of Dipylidium, Echinococcus and Taenia species.
As intermediate hosts, dogs can have cysts of Taenia solium and Echinococcus, but do not show symptoms.
Poultry
As definitive hosts, poultry can have diarrhea and lack of appetite due to the adult tapeworms of Davinia and other species.
As intermediate hosts, they are not important.
Horses
As definitive hosts, horses can be affected by the adults of Anoplocephala. Large numbers of these may cause diarrhea and weight loss.
As intermediate hosts, this is not significant.