Parasitology - Life Cycles, Host Relationships, and Nematodes

Vocabulary flashcards covering core parasitology concepts, host types, symbiotic relationships, helminth classification, diagnostic features, and specific nematode life cycles.

Infective stage

The form of a parasite capable of entering a host and establishing an infection.

Diagnostic stage

The form of a parasite detected in a clinical specimen and used to prove infection.

Endoparasite

A parasite that lives inside the host, such as Ascaris in the intestine or Wuchereria in lymphatic vessels.

Ectoparasite

A parasite that lives on the external surface of the host, such as a louse or tick.

Zoonosis

An infection naturally maintained in animals that can infect humans, with an animal reservoir central to its maintenance.

Definitive host

The host in which a parasite reaches sexual maturity or undergoes sexual reproduction.

Intermediate host

A host that contains essential larval or asexual development of a parasite.

Paratenic host

A transport host that carries an infective parasite without essential development or multiplication.

Reservoir host

A host that naturally harbors a parasite and maintains it as a source of infection for other hosts.

Mutualism

A symbiotic relationship in which both participating organisms benefit.

Commensalism

A relationship in which one organism benefits while the other experiences no significant benefit or injury.

Parasitism

A relationship in which the parasite benefits at the expense of the host, causing harm.

Facultative parasite

An organism that can live independently in the environment but may become parasitic under suitable conditions.

Obligate parasite

An organism that requires a host for at least a necessary part of its life cycle.

Naegleria fowleri

A free-living, thermophilic amoeboflagellate found in warm fresh water and soil that enters through the nose and causes fatal primary amebic meningoencephalitis.

Pseudocoelom

A fluid-filled body cavity between the body wall and digestive tract in nematodes that is not completely lined by mesoderm.

Parthenogenesis

Reproduction from unfertilized eggs, allowing parasitic female Strongyloides stercoralis to produce offspring without a parasitic male.

Nematodes

Elongated, cylindrical, unsegmented roundworms belonging to phylum Nematoda, possessing bilateral symmetry and a complete digestive tract.

Cestodes

Dorsoventrally flattened, segmented tapeworms composed of a scolex, neck, and proglottids that lack a digestive tract.

Trematodes

Unsegmented, leaf-shaped flatworms usually possessing oral and ventral suckers and an incomplete digestive tract.

Ground itch

A pruritic dermatitis caused by infective filariform (L3) larvae of hookworms penetrating exposed bare skin.

Löffler syndrome

A transient eosinophilic pneumonitis caused by helminth larvae migrating through the lungs, classically during Ascaris infection.

Cutaneous larva migrans

An intensely pruritic, raised, serpiginous skin eruption caused by animal hookworm L3 larvae (such as Ancylostoma braziliense) penetrating human skin.

Visceral larva migrans

A condition caused by human ingestion of embryonated Toxocara canis or Toxocara cati eggs, leading to larval migration through organs like the liver and lungs.

Internal autoinfection

A process in Strongyloides stercoralis where rhabditiform larvae transform into infective filariform larvae inside the intestine and penetrate the intestinal mucosa.

External autoinfection

A process in Strongyloides stercoralis where rhabditiform larvae transform into filariform larvae near the anus and penetrate perianal skin.

Strongyloides hyperinfection

An accelerated autoinfection cycle producing massive numbers of Strongyloides larvae in the intestinal and pulmonary pathways, often triggered by corticosteroid therapy.

Calabar swellings

Transient, localized, nonpitting angioedematous swellings caused by immune responses to migrating adult Loa loa in subcutaneous tissue.

Elephantiasis

Persistent lymphedema with thickened fibrotic skin and swelling resulting from chronic lymphatic filariasis caused by adult Wuchereria bancrofti or Brugia malayi obstructing lymphatics.

Cellophane tape test

A diagnostic method for Enterobius vermicularis where clear adhesive tape is applied to perianal skin early in the morning to collect eggs.

Periodicity

The predictable time of day or night when microfilariae reach peak density in peripheral blood.

Strongyloides rhabditiform larva

The L1 larval stage of Strongyloides stercoralis passed in stool, characterized by a short buccal cavity and prominent genital primordium.

Hookworm rhabditiform larva

The noninfective L1 larval stage of hookworms characterized by a long buccal cavity and an inconspicuous genital primordium.

Trichuris trichiura egg

A barrel- or lemon-shaped, thick yellow-brown egg with prominent clear polar plugs at both ends.

Ascaris lumbricoides fertilized egg

A round to oval egg with a thick shell and a mammillated outer coat, passed unembryonated in stool.

Dracunculus medinensis

The tissue nematode transmitted by drinking water containing infected copepods (Cyclops), whose gravid female forms a painful burning skin blister to release L1 larvae.

Onchocerca volvulus

A filarial nematode transmitted by Simulium blackflies near fast-flowing rivers that causes river blindness; microfilariae are unsheathed with no nuclei at the tail tip.