MICRO L8 P2 Cestodes and Taenia Species Overview

Cestodes

• Multi-cellular worms with a flat appearance
• Phylum: Platyhelminthes, Class: Cestoda
• Intestinal Species: Taenia saginata, Taenia solium, Hymenolepis diminuta, Hymenolepis nana, Dipylidium caninum, Diphyllobothrium latum
• Intestinal-Extraintestinal Species: Echinococcus granulosus

Taenia Species

• Two clinically significant species for humans: Taenia solium and Taenia saginata
• Similar characteristics
• Taenia saginata: Common name: Beef tapeworm; Disease: Taeniasis, beef tapeworm infection
• Taenia solium: Common name: Pork tapeworm; Disease: Taeniasis, pork tapeworm infection

Taenia Species - Morphology (Eggs)

• Eggs of T. solium and T. saginata are indistinguishable
• Roundish shape
• Contain a hexacanth embryo with three pairs of hooklets
• Surrounded by a yellow-brown shell (embryophore)

Taenia Species - Morphology (Scolices & Proglottids)

• Scolices (heads): single scolex
• Primary difference between T. saginata and T. solium: T. solium has a rostellum and hooks, T. saginata lacks these features
• Proglottids contain 4 suckers
• Taenia spp are hermaphrodites

Taenia Species - Life Cycle

• Infection occurs by ingesting raw or undercooked beef ( T. saginata) or pork ( T. solium) contaminated with a cysticercus larva
• Cysticercus larva: infective stage, inverted scolex surrounded by a bladder-like cyst filled with fluid.
• Larva releases in small intestine, scolex attaches to intestinal mucosa, matures into adult worm.
• Adult worm produces eggs, some passed in feces, consumed by animals (e.g., cows or pigs)
• Eggs hatch, larva migrates to tissue, becomes an infective cysticercus larva.
• New cycle begins when humans ingest infected animal meat.

Taenia Species – Clinical Symptoms

• Asymptomatic in most infected individuals
• Taeniasis (Beef or Pork Tapeworm Infection): diarrhea, abdominal pain, significant weight loss, vomiting, nausea

Taenia Species – Nutrient Malabsorption & Deficiency

• Competition for nutrients
• Reduced availability of essential nutrients (carbohydrates, proteins, fats)
• Micronutrient deficiencies (vitamin B12, iron)
• Leads to fatigue, anemia, neurological issues
• Diarrhea and appetite loss contribute to nutrient loss

Nematodes (Roundworms)

• Ascaris lumbricoides

Ascaris lumbricoides – Life Cycle

• Only one host: human (no intermediate host)
• Transmission: fecal-oral
• Infective stage: embryonated egg
• Ingested egg hatches in small intestine; migrates through lungs, trachea, pharynx, then to small intestine

Ascaris lumbricoides – Morphology (Eggs)

• Fertilized Eggs: Rounded to oval, laid by inseminated females, embryonated, infective
• Unfertilized Eggs: Rounded to oval, laid by uninseminated females, non-embryonated, not infective

Ascaris lumbricoides – Morphology (Adult Worms)

• Cylindrical
• Female: longer, straight tail, vulva on the body side.
• Male: Curved tail, pair of equal-sized copulatory spicules.

Ascaris lumbricoides – Pathogenicity (Adult Worms)

• Scariasis, caused by both adult worms and migrating larvae
• Severe malnutrition, including vitamin A deficiency, night blindness.
• Growth retardation, intestinal obstruction (heavy infection)

Ascaris lumbricoides – Pathogenicity (Larvae)

• Loeffler's syndrome
• inflammation, hypersensitivity, irritation and wheezing due to larval migration to lungs.

Explore the world of Cestodes, focusing on the Taenia species, including their morphology, life cycle, and clinical significance in humans. Learn about the differences between Taenia solium and Taenia saginata, and their role in taeniasis. This quiz is perfect for students of parasitology and veterinary medicine.