Cestodes Short Note

There are 2 main types of cestodes.

1. Platyhelminthes

2. Nemathelminths

Platyhelminthes

This group consists of flat worms that does not have a body cavity.

This group has 2 main sub-groups

1. Trematoda - Flukes

2. Cestode - Tapeworms

Cestode

These are flat long (ribbon like) segmented worms that has a proglottid.

Cestode body can be divided into 3 main parts

1. Head

   Head of the cestodes is also called the scolex, scolex has 3 main parts

   1. Suckers

   2. Hooks

   3. Grooves

2. Neck

Neck is the region of growth of the cestode. This part generates the segments that are visible in the body.

3. Body

Body of the cestode has 3 regions

1. Region with immature segments

2. Region with mature segments

3. Region with gravid segments

Examples of cestodes

• Highlighted species are not found in Sri Lanka

Transmission

Cestodes are transmitted via ingestion of raw or undercooked meat, this way the cysticercus larvae is ingested and the adult worms make the human body it’s natural definitive host.

Cestode vs Trematode Morphology

1. The head portion of the cestodes and trematodes differs a lot. Cestodes have a cyclophyllidae and trematodes have a pseudophyllidea.

2. Cestodes have a non-operculated egg and trematodes have an operculated egg.

3. Cestode egg contains hooks that is visible in light microscopy

1. Cestode egg has radial striations in the embroyopore.

2. In trematodes the uterine and genital pores are visible in the center of the proglottids.

3. In cestodes the genital pore is in a side of the proglottid and there is no uterine pore, the uterus ends blindly.

4. In trematodes the uterus is coiled. In cestodes it is sac like, branched or contain an egg capsule.

5. Gravid proglottid of trematodes have more (15-30) branches than cestodes (7-12) - this is seen using the mix carmine stain or the India ink stain.

Cestode reproductive system is highly developed. We call it hermaphroditic. Which means it can perform both self-fertilization and cross fertilization. Each proglottid is equipped with both male and female reproductive organs.

If the humans consume meat from pigs they get infected with cysticircus cellulose - mature larvae (adult infection). What will happen if they consume eggs coming from the mature proglottid?

Steps,

1. Cattle and pigs are infected by ingesting grass contaminated with eggs of cestodes.

2. Oncosphere hatch, penetrate the intestinal wall and circulate to muscle tissue.

3. Then the oncosphere develops into cysticerci in muscles.

4. Humans eat the muscle tissue as meat and the protoscolex of the cysticerci gets attached to the intestinal wall.

5. They lay eggs and gravid proglottids in faeces.

Infective stage: Cysticerci bovis

When the human becomes the intermediate host the Cysticerci goes and wreck havoc in the brain and cause Neurocysticercosis, eye, subcutaneous tissue, heart and muscle.

Morphology of Taenia solium

1. Rostellum with 4 suckers.

2. Rostellum has 2 rows of hooks.

3. Gravid segments are longer than broad, egg filled uterus.

4. Scolex is embedded in the jejunal mucosa.

5. No heavy infection, only 1-2 worms.

Treatment

When treating cysticercosis Niclosamide 2g OR Albendazole 8 day course is used, albendazole can penetrate the blood brain barrier therefore it is good for neurocysticercosis.

Intraventricular cysts and cysts in the subarachnoid space can be removed by surgery.

Nemathelminths

This group consists of worms that have a round worms that have a body cavity.