Cestoda: Flat Worms

• Flat, ribbon-like segmented worms
• They are hermaphroditic, but usually need the opposite sex for reproduction
• They have a well-developed reproductive system, tegument, testes, ovaries and uterus for entry/exit of nutrients

Taxonomy

• Platyhelminthes phylum class Cestoda includes Pseudophyllidea and Cyclophyllidea and Trematoda

Cestodes

• Pseudophyllidea and Cyclophyllidea are Flukes.

Larval Stage

• Pseudophyllidea has ovum, coracidium, oncosphere, procercoid and plerocercoid stages
• Cyclophyllidea has ovum, hexacanth oncosphere, oncosphere, cysticercus and cysticercoid stages.

General Characteristics of Pseudophyllidea

• Requires two intermediate hosts and bothria

Cyclophyllidea

• Has acetabula (suckers), possesses a rostellum (armed/unarmed) and 3 main parts

Segments

• Immature segments are nearest to the neck
• Mature segments in the middle, possessing reproductive structures
• Gravid/ripe segments are farthest from the neck and filled with eggs in the uterus that can be detached through apolysis

Life Cycle Notes

• Human infection starts from consuming raw or undercooked beef (T. saginata) or pork (T. solium) contaminated with cysticercus larva
• Adult worms emerge, attach to mucosa and self-reproduce

T. solium Organism

• Can grow 1.5 to 8m long
• Can produce >1000 proglottids each containing 50,000 eggs

T. saginata Organism

• Can grow 4-12m long
• Can contain 1000 to 2000 segments, and produce 100,000 eggs
• Usually one adult is present in T. saginata infections.
• Irritation can be caused by alcohol
• The adult may be irritated by alcohol, with proglottids sometimes resulting after a drinking bout.
• Cows or pigs consume appropriate contaminated eggs and then infective cysticercus larva form.

Taenia Spp

Eggs

• Spherical, striated, embryonated, and contains 6 hooklets
• Motile, called 1st stage larva (due to their motility/movement)

Diagnosis

• Stool sample is test of choice for eggs and gravid proglottids
• The scolex is only seen after treatment

Taenia Saginata Pathology

• Causes Taeniasis
• Non-specific symptoms
• Epigastric pain
• Hunger pangs
• Weakness/weight loss
• Loss of appetite
• Anal pruritus
• Intestinal obstruction caused by tangled proglottids

Taenia Solium Pathology

• In adults the disease is taeniasis
• Presenting symptoms are abdominal discomfort, hunger & malabsorption
• Larval form can cause Cysticercosis
• Symptoms can be more dangerous then the adult
• Can spread to other organs and cause CNS disease or death

Treatment

• Use praziquantel or niclosamide to treat both infections and all scolices should be dissolved

Prevention

• Practice good sanitation and cook meat thoroughly

Hymenolepis Nanna

• Known as Dwarf tapeworm

Hymolepis diminuta

• Known as Rat tapeworm

Common Intermediates

• Dwarf tapeworms use rice/flour beetles
• Rat tapeworms use grain beetles and fleas
• In both, the adult worms form in intestinal mucosa and eggs are deposited in feces

Life Cycle Notes (H. nana)

• Has a dual pathway
• Development can be direct or indirect
• Beetles or fleas ingest contaminated droppings

Life Cycle Notes Continued (H. diminuta)

• Human infection is initiated following ingestion of infective eggs

Scolex

• The Dwarf Tapeworm is subglobular shaped has four cup-like suckers
• Also has retractable armed rostellum
• The Rat Tapeworm has four cup-like suckers
• has rudimentary unarmed rostellum with simple hooklets

Strobila

• The dwarf worm contains 175-220 segments along the same side of its body; the neck is thin
• The rat worm has the genital spores along the same side

Signs

• The dwarf tapeworm is short.
• The rat worm has genital pores and is much wider
• Both worms can cause abdominal pain and anorexia

Clinical Symptoms

• Can cause Hymenolepiasis, abdominal pain, anorexia and diarrheoa
• Eggs can be found in the stool

Treatment

• Praziquantel is effective
• The alternative is Niclosamide

Transmission Prevention

• Proper hygiene required
• Avoid raw seafood or shellfish
• Cook seafood properly

Epidemiology

• H. nana is most common tapeworm
• H. diminuta is worldwide but rare, due to lack of protection of foods from rodents and insects.

Dipylidium Caninum

• Known as the dog tapeworm
• Can utilize many intermediate hosts
• Transmitted by coming into contact with infected cats or dogs
• Eggs can be found in the stool

Treatment

• Praziquantel is the treatment of choice

Echinococcus Granulosus

• Humans can digest eggs from contact with infected animals
• The hydatid cysts develop in the live/lungs

Pathology

• Hydatid dissease, hydatidosis or cystic echinococcosis can occur

Treatment

• Surgical cyst removal with albendazole medication is recommended

Adult

• 3-6mm in length
• It is the shortest tapeworm of man

Scolex

• This species is pyriform and bears armed rostellum
• The organism has three segements

Diphyllbothrium latum

• Broad fish Tapeworm
• Eggs: Ingestion or contamination, Non-embryonic
• Diagnostics Test: Egg sample test of choice if stool sample is given immediately

Symptoms

• Asymptomatic, but can present with digestive issues
• Fish tape worm infection caused by Vitamin B12 deficiency and/or Anemia

Treatment

• Should require follow ups to test for vitamin difficiencies and any associated problems