Class Cestoda
Cestodes (tapeworms) are dorsoventrally flattened, segmented helminths that inhabit the intestinal tract of humans and animals. Their body is divided into a scolex, neck, and strobila composed of proglottids. They lack a digestive system and absorb nutrients through their body surface. Most cestodes require one or more intermediate hosts to complete their life cycle and are hermaphroditic.
Taenia saginata (Beef tapeworm)
Disease: Taeniasis
Morphology
Taenia saginata has a pyriform (pear-shaped) scolex with four hemispherical suckers. There is no rostellum and no hooks, which is the key feature distinguishing it from T. solium.
The mature proglottids show irregular alternate lateral genital pores.
The uterus has numerous lateral branches, more than in T. solium.
The gravid uterus contains ~100,000 eggs and has no uterine pore.
The eggs are indistinguishable from those of T. solium.
Hosts
- Definitive host: Human
- Intermediate host: Cattle (cow, buffalo)
Life Cycle
- Eggs or gravid proglottids are passed with human feces onto soil.
- Cattle ingest eggs while grazing.
- In the duodenum, the egg ruptures and oncospheres are released.
- Using hooklets, oncospheres penetrate the intestinal wall and enter lymphatics or blood vessels.
- They reach circulation via liver → heart → lungs.
- They lodge in striated muscles and develop into Cysticercus bovis (bladder worm).
- Cysticerci are milky-white, ovoid, commonly found in muscles of mastication, tongue, heart, diaphragm, and can survive ~8 months.
- Humans acquire infection by eating raw or undercooked beef containing Cysticercus bovis.
- Larvae excyst in the small intestine, attach to mucosa using suckers, and develop into adult worms.
- Adult worms mature in 2–3 months, produce eggs, and the cycle repeats.