Updated: 12/20/2019

Roundworms (Nematodes)

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  • 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
    • 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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Questions (7)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2

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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? Review Topic | Tested Concept

QID: 109392





Penetration of skin




Animal bite




Insect bite




Sexual contact



L 1 C

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