# 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.

<div data-node-type="callout">
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<div data-node-type="callout-text">These are relatively rarely found in humans and mostly found in animals. They also cause zoonotic infections as well.</div>
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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
    

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<div data-node-type="callout-text">Gravid segment consists of <strong>egg filled uterus. </strong>Gravid segments get detached and passed out with faeces continuously.</div>
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Examples of cestodes

| **Cestode Name** | **Common Name** | **Hosts** |
| --- | --- | --- |
| Taenia solium | Pork tape worm | Only men |
| Taenia saginata | Beef tape worm | Only men |
| <mark>Hymenolepis nana</mark> | <mark>Dwarf tape worm</mark> | <mark>Man, and rodent</mark> |
| Hymenolepis dimunata | Rat tape worm | Man is the accidental definitive host. Naturally infects mice. |
| Echinococcus granuloses | Dog tape worm | Dogs |
| <mark>Diphyllobothrium latum</mark> | <mark>Fish tape worm</mark> | <mark>Fresh water fish (not salt water)</mark> |
| Bertiella struderi | Monkey tape worm | Human |

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<div data-node-type="callout-text"><strong>Bertiella struderi</strong> is the <strong>smallest cestode in Sri Lanka. Taenia saginata</strong> is the <strong>longest cestode</strong> in Sri Lanka.</div>
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<div data-node-type="callout-text"><strong>Diphyllobothrium latum</strong> is the longest cestode in the world.</div>
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<div data-node-type="callout-text">Bertiella struderi gets transmitted to humans through <strong>ingestion of mites that consume monkey faeces.</strong></div>
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<div data-node-type="callout-text">Taenia solium and Hymenolepis nana cause autoinfection.</div>
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* Highlighted species are not found in Sri Lanka
    

|  | **Human as Normal Definitive Host** | **Human as Accidental Definitive Host** |
| --- | --- | --- |
| Adults | Taenia solium. | Hymenolepis dimunata |
|  | Taenia saginata |  |
|  | Diphyllobothrium latum |  |
|  | Hymenolepis nana |  |
| Larvae |  | Taenia solium - in liver, muscle and brain |
|  |  | Echinococcus granuloses - In liver and lungs |

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<div data-node-type="callout-text">Larval stages of <strong>Echinococcus granuloses</strong> cause <strong>hydatid cyst</strong> in humans as an accidental definitive host. Larval stages of <strong>Taenia solium</strong> in humans cause <strong>cysticercosis.</strong></div>
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<div data-node-type="callout-text">Cestodes are not soil transmitted helminths</div>
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### 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.

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## 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
    

<div data-node-type="callout">
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<div data-node-type="callout-text">These hooks (6 of them) are visible in a cestode egg. We call this a hexacanth embryo.</div>
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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.