Updated: 10/30/2020

Roundworms (Nematodes)

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Snapshot
  • A 5-year-old boy is brought to his pediatrician for abnormal scratching behavior. His mom reports that he has been scratching his anus for the past few days, causing some concern among his schoolteachers. His bowel movements and appetite have been normal. On physical exam, there is some erythema and excoriations from scratching around his anus. His pediatrician conducts a scotch tape test and identifies eggs on microscopy. He is given the correct anti-helminthic therapy.
Introduction
  • Introduction
    • helminths are macroscopic parasitic worms
      • tapeworms (cestodes)
      • flukes (trematodes)
      • roundworms (nematodes)
    • roundworms (nematodes)
      • organism characteristics
    • transmission
      • ingestion of eggs/larvae
        • Enterobius
        • Ascaris
        • Toxocara
        • Trichuris
        • Trichinella
        • Dracunculus
      • invasion of larvae cutaneously
        • Strongyloides
        • Ancylostoma
        • Necator
      • arthropod bites
        • Loa loa
        • Onchocerca volvulus
        • Wuchereria bancrofti
    • treatment
      • most are treated with bendazoles
      • other options include ivermectin or diethylcarbamazine
Roundworms (Nematodes)
Organism Clinical Presentation
Transmission Treatment
Transmission by Ingestion of Eggs
Enterobius vermicularis (pinworm)
  • Anal pruritus, especially in children
  • Scotch tape test
    • scotch tape to anal area will show eggs on microscopy
  • Most common helminth parasite in the US
  • Fecal-oral
  • Ingestion of eggs
  • Bendazoles
  • Pyrantel pamoate
Ascaris lumbricoides (giant roundworm)
  • Biliary obstruction
  • Intestinal obstruction or perforation
  • May also affect the lungs
  • Oval eggs are seen on stool microscopy
  • Fecal-oral
  • Ingestion of eggs
  • Migrates from the nose/mouth to intestines
  • Bendazoles
Toxocara canis
  • Visceral larva migrans
  • Myocarditis, liver damage, ocular damage (visual impairment and blindness), and brain damage (seizures and coma)
  • Granuloma formation causes damage
  • Fecal-oral
  • Ingestion of eggs
  • Migrates from intestinal wall to blood
  • Bendazoles
Trichuris trichiura (whipworm)
  • Microcytic anemia
  • Abdominal pain and diarrhea
  • Can cause intestinal/rectal prolapse in children
  • Fecal-oral
  • Ingestion of eggs
  • Bendazoles
Transmission by Ingestion of Larvae
Trichinella spiralis
  • Trichinosis
  • Fever, vomiting, nausea, periorbital edema, and myalgia
  • Undercooked meat
  • Ingestion of larvae (the only nematode transmitted this way)
  • Migrates from blood to striated muscle, causing inflammation
  • Bendazoles
Transmission by Cutaneous Penetration
Strongyloides stercoralis (threadworm)
  • Gastrointestinal upset
  • Pneumonitis
  • Loffler syndrome
  • Dermatitis
  • Rhabditiform larvae, not eggs, seen on stool microscopy 
  • Penetration from soil into the skin
  • Bendazoles
  • Ivermectin

Ancylostoma braziliense

Necator americanus (hookworm)

  • Microcytic anemia
  • Cutaneous larva migrans or "creeping eruption" that moves as the larvae moves
  •  
  • Pruritic serpiginous rash
  • Penetration into the skin, often from walking barefoot on the beach
  • Nematode sucks blood from the intestinal wall
  • Bendazoles
  • Pyrantel pamoate
Transmission by Arthropods (Bite or Ingestion)
Wucheria bancrofti
  • Lymphatic filariasis or elephantiasis
  • Lymphedema causing disfiguration of extremities
  • Via female mosquitoes
  • Invades lymph nodes
  • Diethylcarbamazine 
Loa loa (African eye worm)
  • Calabar swellings in skin
  • Worms in conjunctiva 
  • Via deer flies, horse flies, and mango flies
  • Diethylcarbamazine 
Onchocerca volvulus
  • Hyperpigmented rash, river blindness, and black skin nodules
  • Via female blackflies
  • Ivermectin (Rivermectin)
Dracunculus medinensis (Guinea worm)
  • Skin inflammation and ulceration
  • Worm eruption from skin
  • Anaphylactic shock if worm is pulled from skin and breaks, due to release of foreign antigens
  • Ingestion of water contaminated with infested water fleas
  • Niridazole
  • Removal of worm that has emerged from skin, by a few cms each day using a rod
 
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(M1.MC.17.4817) A 32-year-old woman presents to your office with abdominal pain and bloating over the last month. She also complains of intermittent, copious, non-bloody diarrhea over the same time. Last month, she had a cough that has since improved but has not completely resolved. She has no sick contacts and has not left the country recently. She denies any myalgias, itching, or rashes. Physical and laboratory evaluations are unremarkable. Examination of her stool reveals the causative organism. This organism is most likely transmitted to the human host through which of the following routes? Tested Concept

QID: 109392
1

Inhalation

21%

(31/147)

2

Penetration of skin

54%

(79/147)

3

Animal bite

16%

(24/147)

4

Insect bite

2%

(3/147)

5

Sexual contact

5%

(8/147)

M 1 C

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