Bailey & Scott's Diagnostic Microbiology: Tissue Nematodes Flashcards

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intestinal nematodes

five stages; transmitted by skin puncture, free living soil, and ingestion of raw freshwater fish


tissue nematodes

five stages; transmitted by blood feeding arthropods, ingestion of freshwater crustaceans, and ingestion of contaminated meat


Trichinella spiralis

humans are accidental host which became infected by eating contaminated raw or undercooked meat; infections worldwide; infected mammal definitive host for transmission to humans-domestic pig most important, also bears, walrus, wild game; pseudospiralis and britovi are other species


Trichinella spiralis

encysted larvae ingested from undercooked meat; larvae deposit in striated muscle; adults remain in intestine


Trichinella spiralis clinical presentation

mild sub-clinical to severe illness dependent on parasite burden; nausea, vomiting, abdominal pain, and diarrhea; systemic illness leads to fever, facial edema around eyes, myalgia, marked eosinophilia, larval migration may occur affecting brain and meninges resulting in neurological symptoms, and myocarditis, arrhythmias, and sudden death



distributed worldwide-most commonly in parts of Europe and the US; encysted larvae cause disease of muscle; adults reside in intestine; larvae will not encyst in brain or heart tissue


Trichinosis lab diagnosis

diagnosed with muscle biopsy, nucleic acid based testing, and serology


Toxocara spp.

zoonotic disease with worldwide distribution; persists months to years; humans accidentally ingest eggs; larvae released in small intestine, penetrate and migrate to other tissues (liver and lungs); adults unable to mature in human host; canis-dogs, cati-cats; no eggs in human illness


Toxocara spp. clinical presentation

most infections are subclinical with mild disease; severe forms visceral larva migrans (liver, heart, lungs, kidneys, muscle), ocular larval migrans, covert or common toxocariasis (nonspecific), and neurotaxocariasis (brain and CSF)


Toxocara spp. lab diagnosis

direct examination-stool specimens not useful since there are no eggs; other helminth eggs may be present (risk factor); definitive surgical histopathology of migrating larvae; serology useful, eosinophilia


Dracunculus medinensis

guinea worm acquired from ingestion of infected copepods in freshwater ponds; larvae released form copepods and migrate through thoracic musculature; mating occurs in peritoneal space (male dies, female migrates to surface to lay eggs); dracunculiasis


Dracunculus medinensis clinical presentation

well known presentation, no lab ID; rural, isolated areas of African countries; worms are attached to a stick and slowly retract from host by turning the stick


Ancylostoma spp.

common hookworms of dogs and cats; braziliense and caninum; found in southeastern US; infective larvae penetrate skin of human and migrate through subcutaneous tissue forming tracks; not intestinal; diagnosis made by track evidence


Parastrongylus cantonensis

rat lungworm endemic in SE Asia; rodents shed larvae that infect mollusks (IH) which are consumed by paratenic hosts (shrimp, fish, crabs, frogs) which humans then ingest; larvae migrate to CNS or eye; diagnosis based on histologic exam of adult female


Parastrongylus costaricensis

found in cotton or black rat endemic in Central and South America; cause abdominal angiostrongyliasis- inflammatory bowel lesions, appendicitis symptoms; associated with ingested salad contaminated with infected slugs or snails; diagnosed based on larvae or egg presence in tissue


Gnathostoma spinigerum

gastric spirurid nematode (dogs and cats); larvae hatch in water and infect copepods and humans accidentally ingest larvae from contaminated fish; worms cannot mature in humans and migrate in tissue; diagnosis based off of larvae found in tissue, head contains four rows of cephalic hooklets, and body is covered with transverse rows of spines