Home > D. Systemic pathology > Infectious diseases > helminths

helminths

Wednesday 24 November 2004

Parasitic worms are highly differentiated multicellular organisms. Their life cycles are complex; most alternate between sexual reproduction in the definitive host and asexual multiplication in an intermediary host or vector.

Thus, depending on parasite species, humans may harbor either adult worms (e.g., Ascarus lumbricoides) or immature stages (e.g., Toxocara canis) or asexual larval forms (e.g., Echinococcus species).

Once adult worms take up residence in humans, they do not multiply but generate eggs or larvae destined for the next phase of the cycle. An exception is Strongyloides stercoralis, the larvae of which can become infectious in the gut and cause overwhelming autoinfection in immunosuppressed persons.

There are two important consequences of the lack of replication of adult worms:
- (1) Disease is often caused by inflammatory responses to the eggs or larvae rather than to the adults (e.g., schistosomiasis)
- (2) disease is in proportion to the number of organisms that have infected the individual (e.g., 10 hookworms cause little disease, whereas 1000 hookworms cause severe anemia by consuming 100 mL of blood per day).

Pathology

- helminth infections (helminthiases)

See also

- infectious agents

  • parasites

Videos

- Trichuris trichiura in the caecum

See also

- helminthiases

  • digestive helminthiasis

Portfolio

  • Pulmonary hydatid cysts (pulmonary echinococcosis)
  • Pulmonary hydatid cysts (pulmonary echinococcosis)
  • Cutaneous north american brugiasis (cutaneous filariasis)
  • Cutaneous north american brugiasis (cutaneous filariasis)