Nematodes Life cycle

What is the life cycle of Enterobius vermicularis (Pinworms)?

Ingestion of embryonated eggs; larvae hatch and develop (molts) in small intestine; adults live in large intestine; female migrate out of anus at night

Who can have a retro-infection?

Pinworms

What is the life cycle of Trichuris trichiura (whipworm)

Ingestion of embryonated eggs; larvae hatch in small intestine & penetrate epithelium; 4 molts → immature adults go to large intestine; adults live in colon with their esophagus embedded in host cell syncytium

How do nematodes grow and reproduce?

Nematodes reproduce sexually (males smaller than females) and grow by molting through stages L1 → L2 → L3 → L4 → adult, shedding their cuticle each time

What are the three forms of nematode reproductive output, and examples of each?

• Embryonated eggs (already contain larvae): Enterobius vermicularis

• Unembryonated eggs (develop in soil): Ascaris, Trichuris, hookworms

• Ovoviviparous (release live larvae): Trichinella spiralis, lymphatic filariae

Which nematodes stay entirely in the GI tract, and how?

• Enterobius vermicularis: Ingest embryonated egg → larvae & adults in intestine → females lay eggs perianally; can retro-infect.

• Trichuris trichiura: Ingest embryonated egg → larvae hatch in SI → adults embed in colon epithelium.

Which nematodes migrate through tissues and what are their routes?

• Ascaris lumbricoides: Gut → liver → heart → lungs → trachea → gut (causes pneumonitis).

• Hookworms (N. americanus, A. duodenale): L3 penetrate skin → blood → lungs → pharynx → swallowed → adults in SI; A. duodenale can also transmit orally or via breast milk.

What are examples of nematodes with live birth, vector-borne, or aquatic life cycles?

• Trichinella spiralis: Ingest infected meat → adults in SI epithelium → newborn larvae encyst in muscle (nurse cell).

• Filarial nematodes (Wuchereria, Brugia, Onchocerca): Mosquito/blackfly transmits L3 → adults in lymphatics or skin → females release microfilariae; rely on Wolbachia.

• Dracunculus medinensis: Ingest infected copepods → larvae migrate in tissues → female emerges through skin to release larvae into water.

What is the life cycle of roundworms (w/o wandering)?

Ingestion of egg; Larva hatches in small intestine (bile salts dissolve eggshell), shifts metabolism aerobic → anaerobic, live on chyme & host cell debris; S-shaped configuration against intestine wall, moves against peristalsis; exit through feces

What is the life cycle of roundworms (w/ wandering)?

Wandering phase: penetrates wall, enters capillary;  Circulation to liver (feeds/grows), then heart, then pulmonary circulation; Breaks out into alveolar space; Larvae migrate up trachea, are swallowed; Adults mature in small intestine lumen (~6 weeks). Wandering route: Gut → Liver → Heart → Lung → Trachea → Gut

What is the pathology of Roundworms?

N/A

What is the pathogenesis of roundworms?