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.