Nematodes Life Cycle Stages Quiz

Intestinal Nematodes

• Larval stages of hookworms and Strongyloides: considered as feeding stage, larvae with an open mouth, shorter and robust than filariform larva, not infective.
• Filariform larva: esophagus is uniform throughout, considered as the non-feeding stage, larvae with a closed mouth, longer and slender than rhabditiform larva, infective stage.

Intestinal Parasites

• Ascaris Lumbricoides (roundworms): largest intestinal nematode, common name: giant intestinal roundworm, disease: ascariasis, habitat: intestinal tract, infective stage: ingestion of embryonated ova (fertilized or unfertilized eggs).
• Ancylostoma Duodenale & Necator Americanus (hookworms): disease: hookworm infection, habitat: large intestine, infective stage: ingestion of embryonated ova.
• Trichuris Trichiura (whipworms): disease: trichuriasis, habitat: large intestine, infective stage: ingestion of embryonated ova.

Diagnostic Stage

• Necator Americanus: diagnostic stage: filariform larva, mode of transmission: skin penetration.
• Trichuris Trichiura: diagnostic stage: adult worm, mode of transmission: ingestion of embryonated ova.
• Capillaria Philippinensis: diagnostic stage: adult worm, mode of transmission: ingestion of raw or undercooked fish.

Zoonotic/Non-Human Infection

• Ascaris of dogs: can infect humans, called ascaris.
• Toxocara Canis: can infect humans, disease: visceral larva migrans, transmission: accidental ingestion of embryonated eggs.
• Ancylostoma Caninum: can infect humans, disease: cutaneous larva migrans, transmission: skin penetration.
• Dirofilaria Immitis: can infect humans, disease: produce peripheral nodules in the lungs, transmission: mosquito bite.

Extra-Intestinal Mode of Transmission

• Trichinella Spiralis: transmission: consumption of raw or undercooked meat, especially pork.
• Dracunculus Medinensis: transmission: ingestion of contaminated water.

Ascaris Lumbricoides

• Largest intestinal worm: soil-transmitted helminth, ova: regularly ovoid, with thick shell, cytoplasm contains organized germ cells.
• Adult: lives primarily in jejunum, female: contains egg in its body, body is divided into two parts: anterior and posterior, two types: typical and atypical female.
• Male: has caudal alae, single spicule and unspined sheath, slender than female, stichosome: esophageal structure with rows of secretory cells.

Hookworms

• Necator Americanus, Ancylostoma Duodenale, Ancylostoma Caninum, Ancylostoma Braziliense: blood-sucking nematodes causing anemia, attached to intestinal mucosa, soil-transmitted helminths, capable of heart-lung migration.
• Ova: all hookworm eggs are alike, ovoid, with thin hyaline transparent shell, contains 2-8 germ cells.
• Adult: has a mouth/buccal cavity with dental pattern, Necator americanus: with semilunar cutting plates, Ancylostoma duodenale: with 2 pairs of teeth, Ancylostoma caninum: with 3 pairs of teeth, Ancylostoma braziliense: with 1 pair of teeth.
• Copulatory bursa: structure found among male nematode used for copulation, parts: copulatory spicules and dorsal rays.

Strongyloides Stercoralis

• Smallest nematode of a man: capable of heart-lung migration, mode of living: facultative (free-living/parasitic), parthogenic: can produce eggs even without male.
• Ova: similar to those of hookworms, eggs smaller than those of hookworms, contains larva, referred to as “Chinese Lantern Ova”.
• Larval stages: L1: Rhabditiform (feeding stage), L3: Filariform (infective stage).

Dracunculus Medinensis

• Named by Galen: not a true filaria, larva: have a well-developed digestive tract, never found in blood or tissues of the host, discharged directly into the water.
• Female: ovoviviparous parasite, blister to form, male: inconspicuous.

Trichinella Spiralis

• Parasite of carnivorous mammals: common in rats and in swine fed uncooked garbage, may occur in humans who consume uncooked pork.
• Larva: encysted larva is the diagnostic and infective stage, fully developed, coiled in a spiral and gradually become surrounded by a sheath drive from muscle fibers.
• Adult female: larger, straight, pointed tail, viviparous, single club-shaped uterus containing larva, single ovary.
• Male: curved posteriorly, possesses two pairs of conical papillae, single testis, cloaca found at the caudal end, absent spicule.

Angiostrongylus Cantonensis

• Other name: parastrongylus cantonensis: final/definitive host: Rattus Norvegicus, Rattus Rattus, accidental host: humans, intermediate host: mollusk/snail, paratenic host: prawn, crab, vegetation.
• Infective stage: L3 larva to rats, L1 larva to slugs and land snails.
• Adult: equipped with a uterus with barber’s pole appearance.