Lecture on Clinical Parasitology and Mycology - Nematodes (Roundworms)

Clinical Parasitology and Mycology: Nematodes

Trichinella spiralis and Trichuris trichiura

  • Common Names:
  • Trichinella spiralis: Commonly known as the pork roundworm.
  • Trichuris trichiura: Commonly known as the whipworm.
Life Cycles
  • Construct the Life Cycle:
  • Trichinella spiralis:
    • Ingestion of encysted larvae from undercooked pork.
    • Larvae released in the intestine, mature into adults, and reproduce.
    • Adults produce larvae that migrate to striated muscles, encysting in them.
  • Trichuris trichiura:
    • Ingestion of eggs from contaminated soil (fecal-oral route).
    • Eggs hatch in the intestines, develop into adults.
Hosts
  • Intermediate and Definitive Hosts:
  • Trichinella spiralis:
    • Intermediate host: Pigs.
    • Definitive host: Humans.
  • Trichuris trichiura:
    • Intermediate host: Mainly humans.
    • Definitive host: Humans.
Definitions
  • Free-living: Exists independently in the environment, not requiring a host.
  • Viviparous: Giving live birth rather than laying eggs.
  • Sylvatic Trichinosis: Exists in wild animals but not commonly in humans.
  • Urban Trichinosis: Occurs in humans, often due to consumption of undercooked pork.
Egg Structure of Nematodes
  • Layers of the egg:
  • Fertilization membrane, chitinous shell, outer proteinaceous layer.
Infection and Diagnosis
  • Human and Pig Infection:
  • Humans become infected by consuming raw/undercooked pork.
  • Pigs infected through consumption of infected rodents or carrion.
  • Diagnosis:
  • Serological tests, muscle biopsy to detect encysted larvae.
Nematode Body Structure
  • Body Wall:
  • Contains:
    • Cuticle
    • Basal lamina
    • Hypodermis
    • Muscular layer for movement.
Digestive System Components
  • Digestive System Parts:
  • Mouth
  • Buccal cavity
  • Esophagus
  • Rectum and Anus (females), Cloaca and Anus (males).
Formation from Eggs
  • Juvenile Formation:
  • Development from eggs to L1 (first stage larvae) to adult.

Strongyloides stercoralis

  • Common Name: Known as the threadworm.
Juvenile Forms
  • Rhabditiform Larvae: Early developmental stage, non-infective.
  • Filariform Larvae: Infective stage that can penetrate skin.
Life Cycle Definitions
  • Homogonic Life Cycle: Entirely parasitic with no free-living stage.
  • Heterogonic Life Cycle: Involves both free-living and parasitic phases.
Infection Progression
  • From Free-living to Parasitic:
  • Rhabditiform larvae mature into filariform larvae, which then enter human hosts through skin.
Infective Stage
  • Infective Stage: Filariform larvae (L3) is the infective stage.
Adult Formation
  • Where Adults Form: L3 molts to L4 primarily in the intestines.
Disease Phases
  • Three Phases of Disease:
  • Asymptomatic phase
  • Symptomatic phase
  • Hyperinfection phase.
Diagnosis and Treatment
  • Diagnosis:
  • Stool examination for larvae, serological tests.
  • Treatment: Anti-parasitic medications (e.g., ivermectin).

Ascaris lumbricoides

  • Common Name: Large roundworm of humans.
Sexual Dimorphism
  • Differentiating Males and Females:
  • Males are smaller, have a curved tail.
  • Females are larger and straight.
Copulation and Fertilization
  • Site of Copulation: Occurs in the intestines.
  • Fertilization Location: Eggs become fertile within the intestines.
Larval Pathway
  • Path in Circulation:
  • Larvae migrate to lungs via bloodstream, then are coughed up and swallowed, returning to intestines.
Symptoms and Phases
  • Symptoms:
  • Abdominal pain, malnutrition.
  • Phases:
  • Invasive and intestinal phases.
Treatment and Prevention
  • Treatment: Anti-parasitic medications such as albendazole.
  • Prevention: Proper sanitation and hygiene.

Enterobius vermicularis

  • Common Names: Pinworm and Seatworm.
Nutritional Source
  • Food Supply: Intestinal contents.
Female Activity
  • When to Observe Females: Females are most active at night, laying eggs around the anus.
Egg Fertilization
  • Time for Eggs to Become Fertile: Approximately 6 hours.
Routes of Infection
  • Four Routes:
  • Fecal-oral route, contaminated surfaces, airborne eggs, transmission via clothing.
Infection Prevention and Treatment
  • Preventing Spread: Regular hand washing, cleaning bedding and clothes.
  • Diagnosis and Treatment: Tape test for eggs, anti-parasitic medications.
Characteristics and Symptoms
  • Symptoms:
  • Itching around the anus, irritability, insomnia.
Further Study: Life Cycle
  • Life Cycle Steps:
  • Eggs laid around anus, hatch in intestine, adults live in the colon.

General Morphology of Nematoda

  • Body Structure:
  • Cuticle, basal lamina, hypodermis, muscle tissue to facilitate movement.
  • Digestive System:
  • Organism has a complete digestive system with compartments as described above.
  • Lifecycle Stages:
  • Eggs develop into juveniles (L1 to L4) before maturing into adults.