1. Hymenolepis nana

2. Hymenolepis dimunata

Hymenolepis is a zoonotic infection, infection happens as a result of humans and rodents ingesting cysticercoid infected arthropods. This worm does not leave the intestine and H. nana can cause both internal and external autoinfection but H. dimunata does not cause autoinfection.

Morphology

Hymenolepis nana

1. Has a refractile rostellum with a single row of hooks.

2. Four suckers.

3. Proglottid are broader than the length.

Hymenolepis dimunata

1. Has no hooks on the rostellum.

2. Four suckers.

Cestodes are 15-60mm in length.

Morphology of the Egg

The egg has two membranes, the inner membrane and the outer membrane. There are yolk granules and thread like polar filaments between the two membranes.

The most important point is that both cysticercoid and the adult worm live in the intestine in Hymenolepis dimunata.

In the natural lifecycle of this species the larval and adult stages revolves around the dog and the sheep as shown in this great image I found in CDC website.

There are a few types of echinococcosis

1. Cystic Echinococcosis : Hydatid cysts (Echinococcus granulosis)

2. Alveolar Echinococcosis: Lungs (Echinococcus multiocularis)

3. Neotropical Echinococcosis: (Echinococcus vogeli)

4. Uni-cystic Echinococcosis: (Echinococcus oligarthrus)

Morphology

This worm has 3 segments (or 4 segments including the scolex)

1. Scolex

2. Immature Segment

3. Mature Segment

4. Gravid Segment

Lifecycle Stages in Humans

1. Embryonated eggs in the faeces of dogs.

2. Oncosphere hatches and penetrates the intestinal wall.

3. Hydatid cyst in the liver lungs etc.

Here the cystic lifecycle ends. A canine host is needed to continue the lifecycle beyond the hydatid cyst stage.

Hydatid Cyst

Hydatid cyst is a complex structure it is surrounded by a host collagen capsule. A laminated layer and a germinal layer. Germinal layer generates daughter cells, and they contain Proto scolex.

Daughter cyst rupture and generate sand like structure collected at the bottom of the cyst. This is called hydatid sand, and it can disseminate and infect other parts of the body.

CT, MRI and ultrasound scans and serological diagnosis can be used to identify the parasite. ELISA will need a confirmation with a western blot.

Casoni’s skin test can be used to diagnose this disease.

Treatment

Management of the hydatid cyst is needed. Before surgery Albendazole is used as the drug of choice to prevent dissemination. Removal of cyst fluid and fill the space with Silver Nitrate and 10% formalin for 10 minutes is also done. This will kill the germinal membrane.

After that it becomes safe for a surgeon to cut and drain the cyst. The germinal membrane also needs to be removed while doing so.

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.

"Best way to remember stuff is to try to explain/ teach them to other people"

• Can't remember who said this lol.

So here I am. Drowning in work trying to explain stuff to people on the internet about things in the learning outcomes slide I get on every lecture I visit so bear with me.

The main thing that you need to understand is there are only two ways for things to be transported passively in biological systems. The molecule of interest which can either be a charged particle like an ion or something that does not have a charge like a glucose molecule has to either follow a chemical or an electrical gradient. Electrical gradients only apply to charged particle. Donnan effect is all about the equilibrium between the Electrical and Chemical gradients in a system hence it only applies to ions.

Imagine a system that has three types of ions, Cl^-, Na⁺ and some charged protein, let's call it prot^-.

Now there is a membrane that divides the system which is only permeable to Chloride and Sodium ions. Prote^- are trapped in one side. This effects the net outflow of Sodium ions from that compartment because it is attracted to Prote^-. Therefore, when the system is in equilibrium.

[Na⁺]^{compartment with protein-} > [Na⁺]^{compartment without protein-}

and

[Na⁺]^x + [Cl^-]^x + [Prot^-] > [Na⁺]^y + [Cl^-]^y

This also brings up a really interesting connection that looks like this

[Na⁺]^x / [Na⁺]^y = [Cl^-]^x / [Cl^-]^y

but this is not what happens in cells. Cells have charged proteins in their plasma therefore the ion concentration ( according to Donnan ) has to be always higher than the surrounding extracellular fluid and the cells should rupture due to them being hypertonic but this is not the case. Cell plasma membrane has pumps called Na, K ATPase that actively (which means it uses energy) to pump ions back out of the cells.

The main reason I decided to blog is to curb myself from getting drowned in social media (Hello, Twitter). I recon writing about stuff I find interesting may keep me occupied. Blogging about software development related things is nothing new. It is considered a great way to understand concepts and help another person do the same at the same time. I have no idea whether this would work in health sciences but let's not be quick to judge.

I may get really busy and disappear for long chunks of time. However, I'll always try to at least push something once per week.

So, off we go.