Question

Identify the definitive and intermediate host of the Taenia solium
A. Pig
B. Human
C. Fly
D. All of the above

Answer 1

Hint: The life cycle of Taenia solium is indirect and it passes through various organisms throughout its growth.

Complete Answer:
- Taenia solium, the pork tapeworm, belongs to the cyclophyllidean cestode family Taeniidae. It is found throughout the world and mostly in countries where pork is eaten. Two types of infection occur generally, primary hosting and secondary hosting.
- Primary hosting occurs when under-cooked pork is consumed that contains cysts and results in adult worms in the intestine. This type is generally without symptoms and the tapeworm can be eliminated with medications.
- The other form, secondary hosting, is due to the consumption of water or food that is contaminated by the feces from someone infected by the adult worms. In this case, the eggs are ingested which develops cysts mainly in the muscles and is usually without any symptoms.
- But, some people develop symptoms and the most chronic occurs when the cyst develops in the brain. This condition is called cysticercosis. Treatment for this form is difficult.

The Life cycle in both the hosts are as follows:
(I) Definitive host- Humans ingest the raw or undercooked pork containing the larvae (cysticerci). Inside the body, the cyst evaginates, attaches to the small intestine with their scolex, and mature into adult worms in about 2 months. Adult worms produce proglottids, which become gravid. They detach from the worm and reach the anus. The detached proglottids and the eggs are passed from the definitive host through feces.

(II) Intermediate host- Pigs become infected by ingesting the egg or gravid by contaminated vegetables with traces of human feces. The eggs, then, hatch and release oncospheres which penetrate the intestinal wall. Through the bloodstream, the oncospheres reach the striated muscles and to the brain, liver, and other organs, where they develop into cysticerci. This can result in Cysticercosis. Humans can also, sometimes, become the secondary host by consuming fecally contaminated food.

Thus, the definitive host is human and pigs are often the intermediate or secondary host. In people who do not eat pork, flies and other indirect means of transmission occur which can lead to cysticercosis.

Thus, the correct option is option D, ‘All of the above’.

Note: While Taeniasis is caused by the infection by adult T. solium, Cysticercosis is caused by the ingestion of T. solium eggs or egg-containing proglottids which ruptures in the host intestines. Cysticercosis is the predominant form and can occur from unhygienic areas. The primary cause of this is dirty hands.