questions 4

Roundworms (Nematodes)

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Topic updated on 11/07/17 4:19pm

Introduction
  • Classification
    • Helminths infections include
      • tapeworms (cestodes)
      • flukes (trematodes)
      • roundworms (nematodes) (this topic)
        • roundworms are broken down into
          • transmitted by the ingestion of eggs
            • Enterobius vermicularis
            • Ascaris lumbricoides
            • Trichuris trichiura
            • Toxocara canis 
          • transmitted by the invasion of lavae through the skin
            • Strongyloides stercoralis
            • Ancylostoma braziliense/caninum
            • Necator americanus 
          • transmitted by the ingestion of larvae
            • Trichinella spiralis 
          • transmitted by arthropods
            • Wucheria bancrofti
            • Loa loa
            • Onchocerca volvulus
            • Dracunculus medinensis 

 

Transmitted by the ingestion of eggs ("EATT")
Enterobius vermicularis
  • Introduction
    • also known as pinworms
    • transmitted by ingestion of eggs
  • Diseases
    • perianal pruritis
      • intestinal infection with anal itching
      • scotch tape on anal area to diagnose presence of microscopic eggs
      • initial infection is from contaminated food
      • hand-to-mouth after scratching perpetuates infection
      • most common helminth parasite in U.S.
  • Treatment 
    • -bendazoles
    • pyrantel pamoate

 

Ascaris lumbricoides
  • Introduction
    • also known as giant roundworm
    • most common helminth parasite worldwide
      • in U.S., seen in mountainous south
    • transmitted by ingestion of eggs
  • Diseases
    • ascariasis 
      • GI and pulmonary symptoms
      • lifecycle involves intestine → lungs → intestine
        • eggs ingested
        • larvae penetrate intestinal wall  
        • hematogenous dissemination to lungs
        • growth in alveoli
        • coughed up
        • swallowed
        • mature in intestine
        • excreted in feces
      • eggs visible in feces 
  • Treatment
    • -bendazoles
    • pyrantel pamoate

 

Trichuris trichiura
  • Introduction
    • also known as whipworm
    • slow lifecycle
    • transmitted by ingestion of eggs
  • Diseases
    • intestinal prolapse
    • abdominal pain and diarrhea
  • Treatment
    • -bendazoles

 

 

Toxocara canis
  • Introduction
    • also known as dog roundworm
    • transmitted by ingestion of eggs
  • Diseases
    • visceral larva migrans
      • larvae wander through body causing inflammation
    • granulomas
      • leads to blindness if in retina
  • Treatment
    • albendazole
    • mebendazole

 

 

 

Transmitted by the invasion of larvae through the skin ("SANd")
Strongyloides stercoralis
  • Introduction
    • also known as threadworm
    • larvae in soil penetrate skin 
    • lifecycle involves intestine → lungs → intestine (see above)
    • eggs are not present in stool
    • autoinfection perpetuates indefinitely if not treated
  • Diseases
    • GI
      • vomiting, diarrhea, malabsorption, anemia, ulcers, bloody stools
    • pneumonitis
  • Treatment
    • -bendazoles
    • ivermectin

 

Ancylostoma braziliense/caninum
  • Introduction
    • also known as dog and cat hookworm
  • Diseases
    • cutaneous larva migrans
      • also known as "creeping eruption"
      • raised, red, itchy rash that moves as larvae move
  • Treatment
    • -bendazoles

 

 

 

Necator americanus
  • Introduction
    • also known as new world hookworm
    • larvae enter through intact skin of bare feet
    • lifecycle involves intestine → lungs → intestine
  • Diseases
    • anemia
      • sucks blood from intestinal walls
    • pneumonitis
      • if migration to lungs
  • Treatment
    • -bendazoles
    • pyrantel pamoate

 

 

Transmitted by the ingestion of larvae
Trichinella spiralis
  • Introduction
    • only helminth tested on Step 1 transmitted by ingestion of larvae
  • Diseases
    • trichinosis
      • larvae encyst in muscle causing inflammation and pain
      • periorbital edema
      • larvae ingested from undercooked meat
        • usually pork
  • Treatment
    • -bendazoles

 

 

Transmitted by arthropods
Wucheria bancrofti
  • Introduction
    • transmitted by female mosquito bite
      • symptoms develop 9-12 months after bite
  • Diseases
    • elephantiasis
      • blockage of lymphatic vessels leads to swelling disfiguration of extremities
  • Treatment
    • diethylcarbamazine
Loa loa
  • Introduction
    • also known as African eye worm
    • transmitted by Chrysops (deer fly), horse fly, and mango fly bites
  • Diseases
    • worms in conjunctiva
    • Calabar swelling
      • painful, subcutaneous swelling of skin
  • Treatment
    • diethylcarbamazine
Onchocerca volvulus
  • Introduction
    • transmitted by female blackfly bite
  • Diseases 
    • river blindness
      • microfilariae (larvae) migrate to eyes causing blindness
      • thickened, hyperpigmented skin ("lizard skin")
    • allergic reaction to microfilariae is possible
  • Treatment 
    • ivermectin ("to cure rIVER blindness")

 

 

Dracunculus medinensis
  • Introduction
    • also known as guinea worm 
    • transmitted through drinking water infected with copepods (small crustaceans)
    • eradicated except in Africa
  • Diseases
    • skin inflammation and ulceration
    • worm eruption from skin
      • female pokes through host to expose uterus in order to transmit eggs
  • Treatment
    • niridazole
    • slow worm removal with stick


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(M1.MC.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? Topic Review Topic

1. Inhalation
2. Penetration of skin
3. Animal bite
4. Insect bite
5. Sexual contact

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