Nematodes and Parasitic Roundworms

Nematodes (Roundworms)

Intestinal Nematodes

• Capillaria philippinensis: also known as Pudoc's worm or mystery worm; only nematode whose life cycle involves a migratory bird; natural definitive hosts are fish-eating birds, and incidental definitive hosts are humans; intermediate hosts are freshwater or brackish water fish.
• Ascaris lumbricoides: also known as giant intestinal roundworm, lumbricus teres, or eeworm; largest nematode of man; most common nematode infecting man; soil-transmitted helminth (STH); has heart-lung larval migration.
• Trichuris trichiura: also known as whipworm; eggs are "D-shaped" and have a triple albuminous covering, an inner lipoidal membrane, and no glycogen layer; eggs become infective outside the host for 4-6 hours.

Extra-Intestinal Nematodes

• Filarial Nematodes: includes Wuchereria bancrofti, Brugia malayi, and Loa loa; transmitted by mosquitoes or flies; infective stage is L3 larvae; diagnostic stage is microfilariae in blood or skin.
• Trichinella spiralis: also known as Trichina worm, Muscle worm, or Garbage worm; has three subspecies: T. spiralis spiralis, T. spiralis nativa, and T. spiralis nelsoni; hosts serve as both final and intermediate hosts; intermediate hosts are pigs.

General Characteristics

• Body structure: elongated, unsegmented bodies with cylindrical shape and bilateral symmetry; complete digestive tract; no circulatory system; light cream-white color; separate sexes, some are pathenogenetic.
• Muscular pharynx: triradiate.
• Supporting body wall: outer, hyaline noncellular cuticle; subcuticular epithelium; layer of muscle cells.
• Sensory organs: amphids in anterior ends and phasmids in posterior ends.

Diagnostic Tools

• Basic diagnostic tool: agents, modes of transmission, infective stages, and diagnostic stages.
• Eggs: morphology and characteristics vary depending on the species.
• Larvae: morphology and characteristics vary depending on the species.

Salient Features and Presentation

• Enterobius vermicularis: most common helminth infection in developed nations; most common cause of pruritus ani among school-aged children; increases the risk for UTI; can be transmitted via inhalation of eggs or ingestion of embryonated eggs.
• Ascaris lumbricoides: largest nematode of man; most common nematode infecting man; soil-transmitted helminth (STH); has heart-lung larval migration.
• Capillaria philippinensis: only nematode whose life cycle involves a migratory bird; natural definitive hosts are fish-eating birds, and incidental definitive hosts are humans; intermediate hosts are freshwater or brackish water fish.
• Trichinella spiralis: host serves as both final and intermediate host; intermediate hosts are pigs; three subspecies: T. spiralis spiralis, T. spiralis nativa, and T. spiralis nelsoni.

Diagnosis and Management

• Diagnosis: varies depending on the species, but may include direct fecal smear, Kato Thick smear, Kato Katz smear, Scotch tape test, or muscle biopsy.
• Treatment: varies depending on the species, but may include Albendazole, Mebendazole, or Pyrantel pamoate.

This quiz covers different types of nematodes, including intestinal and extra-intestinal parasites, such as hookworms, filarial nematodes, and trichinella spiralis.