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Enteric Nematodes
Ascaris lumbricoidesEnterobius vermicularisTrichuris trichiuraHookworms
Ancylostoma duodenaleNecator americanus
Strongyloides stercoralis
What you should know about the Enteric Nematodes
Name of organism and diseaseTransmission (how acquired?)Location and migration in humanMajor clinical manifestations including
presence/absence of eosinophiliaDiagnostic tests
Organism: Ascaris lumbricoidesDisease: Ascariasis
Geographical Distribution:Worldwide1.2 billion infected (20%); 20,000 deaths
Transmission:Ingestion of OvaFecal contamination of water, soil and hands
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Larvae hatch in GI tract, penetrate GI wall,
migrate via lungs & bronchi back to GI(Adult stage)
Ascaris lumbricoidesLocation of Parasite
Ascaris lumbricoidesMorphology: Adult, 20-35 cm
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Male
Female
Ascaris lumbricoidesMorphology: Ova
Unfertilized
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Fertilized
EmbryonatedInfective
Ascaris lumbricoidesClinical:
Larval migration in lungs usually asymptomatic, but may be transient eosinophilia
Intestinal stage may produce abdominal pain, diarrhea & non-specific gastrointestinal complaints
Intestinal obstruction
Organism: Enterobius vermicularis PINWORM
Disease: Enterobiasis
Geographical Distribution:Worldwide, 20-60% school age children
Transmission:Ingestion (and inhalation) of eggs
Location of Parasite:Adults in proximal intestine, cecum & appendixnocturnal deposition of eggs on perianal area
Morphology:Adults are 1 cm
Clinical:Asymptomatic, vaginal pruritisNo migration, No eosinophiliaReinfection common
Enterobius vermicularis
Organism: Trichuris trichiuraWHIPWORM
Disease: Trichuriasis
Geographical Distribution:Worldwide
Transmission:Ingestion of eggs
Location of Parasite:Adult embedded in mucosa of cecum,
colon, & rectum
Morphology: Adult 3-5 cmAnterior (digestive) end is thinPosterior (reproductive) end is thick
Trichuris trichuria
Trichuris trichuria
Clinical:Light infections - asymptomaticHeavy infections - diarrhea
bloody diarrhea, rectal prolapse
Diagnosis:O&P Test
Control & Treatment: Mebendazole & Albendazole
Organism: Ancylostoma duodenale & Necator americanus HOOKWORMS
Disease: Hookworm anemia
Geographical Distribution:Humid areas with poor sanitation
Transmission:Direct penetration of unbroken skin by larva
Location of Parasite:Adults attached to mucosa of duodenum and proximal small intestine
Morphology:Adults are 1 cm
Ancylostoma duodenale& Necator americanus
Clinical:Red pruritic lesions at site of larval penetrationEosinophilia possibleAsymptomaticGastric pain & diarrheaAnemia (due to blood loss)
Diagnosis: O&P Test
Control & Treatment: Mebendazole & Albendazole
Ancylostoma duodenale& Necator americanus
Organism: Strongyloides stercoralisDisease: Strongyloidiasis
Geographical Distribution:WorldwideHumid areas with poor sanitation
Transmission:Direct penetration of unbroken skin by larvaAutoinfection - internal (larva becomes infectious in intestinal tract) & external
Location of Parasite:Larva migrates via blood system to lungs,penetrates alveoli,coughed up and swallowed
Adult in mucosa of duodenum & jejunum
Eggs hatch in intestine
Larvae (non-infective) in stooldevelops into infective larva in soil(Free living cycle in soil)
Strongyloides stercoralis
Strongyloides stercoralis
Clinical:Pruritic rash associated with larval entryCoughing & wheezing, High eosinophiliaAbdominal pain, diarrhea
Hyperinfection - large numbers of larvae
Disseminated strongyloidiasis - in other organs (in immunocompromized patients - but not AIDS)
Control & Treatment: Ivermectin, thiabendazole
Diagnosis:String Test Baermann concentration
Serology & Bacterial agar plate
Strongyloides stercoralis
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