Cestodes: Flatworms and Tapeworms

• Lecture covers Cestodes, also known as Flatworms or Tapeworms, are multicellular worms with a flat or ribbon-like appearance

General Characteristics

• Cestodes' eggs are generally not motile, but cestode eggs themselves are motile and able to move around
• The first larval stage has six small hooks, called hooklets, arranged in pairs, which pierce the intestinal wall of the infected host
• Larval forms aren't seen in human specimens
• The tegument absorbs nutrients and excretes waste through the outer surface
• Adult parasites in this group have reproductive systems but lack a digestive tract

Common Features of Adult Cestodes

• The scolex/head (anterior end) has four cup-shaped structures called suckers/Acetabula
• These suckers facilitate attachment to the intestinal mucosa of the infected host
• Some species have a fleshy extension called a Rostellum, that may contain one or two rows of hooks
• The neck region connects the scolex to the rest of the worm
• The strobila/body is a series of proglottids
• Proglottids are individual segments equipped with both male and female reproductive organs

Internal Structures

• Cestodes are hermaphroditic; both male and female reproductive organs are present in the mature proglottid, allowing self-fertilization
• Following self-fertilization, pregnant (gravid) proglottids consist of a uterus filled with eggs
• Gravid proglottids rupture and release eggs into the intestine
• Eggs are usually passed into the outside environment via the stool

Clinical Parasitology: Pathology and Symptoms

• Immature proglottids are small lacking reproductive organs (closest to scolex)
• Mature proglottids develop both male and female reproductive organs
• Gravid proglottids are filled with eggs
• Liver and lung involvement are common in people infected with E. granulosus
• Affected patients may develop a persistent cough, localized pain, and eosinophilia
• Anaphylactic shock, which produces large histamine amounts and other chemical mediators, may develop under appropriate conditions and can be fatal
• Often asymptomatic
• Symptomatic cases present with gastrointestinal discomfort, diarrhea, and abdominal pain
• Can also cause intestinal obstruction and vitamin B12-induced macrocytic anemia, especially with Diphyllobothrium latum

General Laboratory Diagnosis

• Stool exams can detect eggs, gravid proglottids (occasionally), and scolices (rarely, after treatment)
• Tissue biopsy is used for E. granulosus
• Serologic tests

Taenia Species

• Taenia solium is Pork Tapeworm, Taenia saginata is Beef Tapeworm, and Taenia asiatica is Asian tapeworm
• Infection is highly related to eating raw and improperly cooked meat

Taenia spp. eggs

• Somewhat roundish
• Contain a hexacanth embryo with the standard three pairs of hooklets
• Some tapeworm eggs have a yellow-brown shell called an embryophore with distinct radial striations

Taenia spp. proglottids

• T. solium’s are square in appearance
• Have 7 to 15 uterine branches on each side of the uterus (7 to 13 lateral branches)
• T. saginata’s are typically rectangular
• Have 15 to 30 uterine branches on each side (15 to 20 lateral branches)

Taenia Terms

• Proglottid: segment or body part of a tapeworm
• Gravid proglottid: segment filled with eggs
• Oncosphere: embryonated egg or hexacanth embryo
• Scolex: anterior part of the tapeworm responsible for intestinal wall attachment
• Cysticercus/Cysticerci: larval stage where oncospheres develop and migrate to form cysticerci in tissues

Key Facts for Taenia solium

• Pork Tapeworm
• Disease: Taeniasis or Cysticercosis
• Eggs are indistinguishable from T. saginata
• Is distinguished via its scolex

Key Facts for Taenia saginata

• Beef Tapeworm
• Disease: Taeniasis

More Taenia Facts

• T. saginata’s vagina has a sphincter
• Gravid proglottids of T. saginata are most distal from the neck
• Gravid proglottids undergo apolysis and are either passed out with feces or actively crawl out of the bowel
• Invaginated: in muscle tissue
• Evaginated: scolex attached to mucosa of the small intestine

Taenia Treatment notes

• T. solium: Both Cysticercosis & Taeniasis are present
• Taeniasis caused by ingestion of cysticerci from undercooked pork with Cysticercosis caused by ingestion of T. solium eggs, leading to larval development in various human tissues, including the brain (NCC)
  • Cyticercus cellulosae is found in pigs & man
• T. saginata: Only Taeniasis is present, no Cysticercosis
• Taeniasis is caused by ingestion of cysticerci from undercooked beef with Cysticercus bovis found in cattle
• Measly pork - Improperly cooked meat/ infected meat

Clinical Manifestations of Taenia

• Taenia solium
• TAENIASIS (intestinal infection): Mild, non-specific abdominal complaints
• CYSTICERCOSIS (tissue involvement): Cysticerci develops in any organ or tissue, develops in the brain causing NCC (Neurocysticercosis)
  • Convulsion, Visual & motor deficits, Vomiting, and Headache
• Taenia saginata
  • Most common chief complaint is the passage of proglottids or segments in the stool
  • Mild irritation at the site of attachment.
  • TAENIASIS (non specific symptoms)
    • Epigastric pain, Vague discomfort, Hunger pangs, Weakness, Weight loss, Loss of appetite, Pruritus ani (perianal itching)
  • Entangled proglottids result into intestinal obstruction (Rarely)
  • Obstruction in the bile and pancreatic ducts, as well as appendix (due to actively motile proglottids)

Laboratory Diagnosis of Taenia

• Stool examination will show identification of eggs & proglottids
• Eggs: Indistinguishable with T. saginata
• Gravid proglottids:
  • T. solium has 7 to 15 lateral branches
  • T. saginata has 15-20 lateral branches
• Other tests: Serum to test for ELISA (Enzyme-Linked Immunosorbent Assay), EITB (Enzyme-Linked Immunoelectrotransfer Blot), or Western blot (IgG; IgM)
• First specimens usually brought in by patients are the gravid proglottids, either single or in chains
• Gravid proglottids are pressed or flattened in between two glass slides and are examined against the light (Used for a rough count of the lateral branches from the main uterus. or for injection of India ink through the genital pore for an accurate count)
• Examination of eggs are performed with: FEACT, DFS
• Perianal swabs will show eggs left in perianal skin as the gravid segments squeeze out of the anal opening

Taenia Treatment

• The drug of choice for T. saginata is praziquantel
• The drugs of choice for T. solium - Taeniasis are praziquantel and niclosamide (Delay is not recommended because of the theoretical possibility of autoinfection and subsequent cysticercosis)
• Praziquantel works against is affective against the entire adult form (Though isn’t used where there is ocular or CNS involvement)
• Paramomycin & quinacrine hydrochloride (Atabrine) may also be used as alternative
• For managing Taenia NCC, Albendazole is administered at 400 mg twice daily for 8 to 30 days where Praziquantel at a dose of 50 to 75 mg/kg divided into three doses is used for 30 days
• Corticosteroids or Subarachnoid form require surgical removal
• Praziquantel paralyzes the tapeworm, resulting in removal from the intestine, where Albendazole disrupts metabolism of the parasite, leading to its death
• Niclosamide inhibits glucose uptake of the tapeworm
• in T. saginata in PH, with surveys showing pigs affected more

Hymenolepis diminuta

• Common name: Rat tapeworm
• Disease: Hymenolepiasis, rat tapeworm disease
• Requries intermediate host

Hymenolepis diminuta: eggs

• Hexacanth embryo containing three pairs of hooks
• Hooklets shaped in a fan-like arrangement
• Presence of Bipolar thickenings but lacks the bipolar filaments
• A shell surrounds the embryo exhibits distinct polar thickenings but with no polar filaments
• Undergoes Bile stained embryophore

Hymenolepis diminuta: scolex and proglottids

• The scolex: Equipped with four suckers and has a smaller unarmed (No hooks) rostellum that protrudes from anterior
• The proglottids: Typically rectangular (twice as wide as long) where each mature proglottid will have 1 set of each reproductive organ
  • Contains three ovoid testes and one ovary in a more or less straight pattern across segment
  • A saclike Gravid Proglottid filled with eggs that occupy most of space
  • Contains/undergoes Unilateral genital pores

Hymenolepis diminuta: Life Cycle

• Eggs, when ingested by wide range of insects (fleas, beetles, cockroaches, mealworms, and earwigs) develop into infective cysts
• When infected insects are ingested by humans or rat; they develop into the adult form

Hymenolepis diminuta: Treatment of disease

• Humans are accidental host for this infection
• Treat with by ingesting Praziquantel at 25mg/ kg for single dose
• Use Niclosamide to treat (effective alternative form)
• Transmuted through infected fleas that come into contact with food or drinks

Hymenolepis diminuta: Diagnostic Process

• Will experience zoonotic infections or zoonoses
• Use a Stool Exams to diagnosis
• To Identify: Eggs, Scolex (in rare conditions)
• Identifiable by non-circular shapes, larger sizes, Lack of filaments, or a present scolex
• Clinical manifestations:
  • Will cause minimal and no specific detections (but life span is short - not severe in humans)
  • Diarrhea, Nausea, Stomach pain, Lack of hunger

Hymenolepis nana

• Common name: Dwarf tapeworm
• Disease: Hymenolepiasis, dwarf tapeworm disease
• The smallest species of Tapeworms to infect
• Complete life cycle in single host
• Capable of harboring larvae AND completing life cycle
• spherical or subspherical
• Conspicuous poles where thick membrane meets
  • 4-8 hair like structures are implanted in inner membrane
  • Filaments are attached in inner memmrabne
  • Has 3 pairs of hooks, where there is complete protection

Keynote details

• Some eggs will die immediately after released
• Centralized hook
• Contains/produces colourless embrophore

Proglottids details

• equipped with 4 suckers with sub globular shape
• Short hooks attached

Taenia Treatment notes

• Require Praziquantel - paralysis tapeworm leads to removal from intestine
• Albendazole - disrupts the parasites and inhibits spread
• Transmission can happen via hand to mouth spread

Transmission stages include these conditions

• Infected insect is ingested by mammals
• Infected by contamination of food

diphyllo-bothrium Latum

• Broad tape form and infection

Diagnostic notes

• Progolotidds don’t disintegrate and get released
• Capsules extremely hard to pick up

Eggs Features

• Thick shell with some operculum
• knob-like thickienknig

Scolex FEATURES

• Contains both bothria (sucking)
• Almond shape

Treatment

• Can give praziquantel
• Should not take B12

Clinicals notes include

• Not severe or extreme short diseases
• Causes diaherra, nauseous symptoms, stomach pains

Echinococcu granulosa

• tape form - dog
• Larave cycts in humans form in tissue

Adult stages of E - granulosus

• short neck with 3 - 4 segments

egg features

• islar ave stage
• contains brood capsules and outer wall segments

Adult is usually

• scolices 4 sucker