Practical Parasitology

Taenia Species

• Egg size: 30 - 40 microns
• Adult worm size: This varies according to the number proglottids that make up the worm.
• T. saginata and T. solium are typically called the beef and pork tapeworm respectively.
• Each egg has 3 pairs of hooklets and a striated outer shell.
• The eggs of these two species cannot be differentiated.
• If differentiation is required, besides any relevant clinical aspects, an examination of a gravid proglottid is needed.

Click on the images below to enlarge

Taenia proglottid comparison chart from Brown and Belding(3)

Taenia species Life Cycle

Both species of Taenia have a typical life cycle, but T. solium has the ability to autoinfect. In the typical life cycle, the worms present in the intestine of man expel their eggs in the gravid proglottids that separate from the main body of the worm and are passed in feces. New proglottids are formed from the scolex. The eggs are then ingested by cattle or pigs along with their feed. In both species the embryo hatch from the egg and penetrate the mucosa gaining access to the blood they travel to various tissues in the animals body to form cysticerci.

Ingestion of undercooked pork or beef containing cysticerci allow the adult worm to mature in humans. Autoinfection occurs when man is infected with Taenia solium. The embryo hatch from the egg in the intestine and penetrate the intestinal wall where they gain access to the blood stream and travel to various tissues in our body to form cysticerci. This condition is called cysticercosis.

Identification of Taenia species Proglottids by Injection or Section and Staining

Because T. saginata cannot be differentiated from T. solium by the morphology of their ova alone, it is necessary to obtain a gravid proglottid in saline for india ink injection or a proglottid in formalin for section and staining with H&E. If however a scolex is recovered and it does not have hooklets visible it is that of Taenia saginata.

In both cases it is necessary to count the number of lateral uterine branches on one side of the main branch of the uterus. Ink injection method is as follows.

1. Obtain a gravid proglottid in saline.
2. Place the proglottid in saline preferably in a petri dish.
3. Using India ink and a very fine needle or glass pipette inject the ink into the main branch of the uterus.
4. Place the proglottid on a glass slide, cover it with another slide and press together.
5. Count the number of lateral uterine branches on one side of the main branch.
6. Taenia saginata has approx. 15 - 20 branches and T. solium 7 - 13. See diagram below.

A note on section and staining. If the proglottid is received in formalin or SAF it may be sectioned and stained in Haematoxylin and Eosin.

Click on the image to enlarge.

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