Helminth infections

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  • Approximately 2 billion people infected worldwide
  • Many are WHO-designated Neglected Tropical Diseases
  • At-risk populations include impoverished, children, immigrants, tourists, HIV/AIDS patients, refugees
  • Most common in subtropical and tropical areas, moist climates, poor sanitation and hygiene


  • Roundworm (Ascaris lumbricoides, Toxocara canis)
  • Whipworm (Trichuris trichiura)
  • Hookworm (Necator americanus, Ancylostoma duodenale)
  • Tapeworm (Diphyllobothrium latum, Echinococcus granulosus)
  • Cysticercosis (Taenia solium, Taenia saginata)
  • Lymphatic filariasis (aka Elephantiasis; Wuchereria bancrofti, Brugia malayi, and Brugia timori)
  • Dracunculiasis (aka Guinea Worm disease; Dracunculus medinensis)
  • Onchocerciasis (aka River Blindness; Onchocerca volvulus)


  • No direct person-to-person transmission
  • Fecal-oral transmission (ingestion of eggs in contaminated soil / vegetables / water)
    • Ascaris and whipworm from human feces
    • Toxocara from dog / cat feces
    • Echinococcus from sheep / cattle feces
    • Taenia eggs from human feces
  • Cutaneous transmission
    • Hookworm eggs hatch in the soil, mature larvae penetrate skin
    • Lymphatic filariasis transmitted via bite from infected mosquito (Anopheles, Aedes, and Culex)
    • Onchocerciasis transmitted via bite from blackflies (Simulium species)
  • Food or waterborne transmission
    • Taenia also transmitted by ingestion of larval cysts in undercooked pork or beef
    • Diphyllobothrium tapeworm transmitted by contaminated freshwater fish
    • Dracunculiasis transmitted by ingestion of infected Cyclops water fleas in contaminated water (adult worm erodes through skin of leg, releases larvae in water when host wades in pond / open well, infecting the water fleas)


  • Parasitic infections can be in the differential diagnosis for nearly every sign/symptom (GI, dermatologic, neurologic, pulmonary, ophthalmologic, hematologic)
  • Obtain a travel history in every patient
    • countries of travel
    • duration of stay
    • activities while traveling (adventure travel, tourism, working, swimming)
    • living arrangements – city / village / hotel / tent
    • drinking water source
    • symptom chronology

Clinical Features

Soil-transmitted helminths (Ascaris roundworm, whipworm, hookworm)

  • Morbidity is related to number of worms harbored in intestines
  • Light infections often asymptomatic
  • Heavier infections with variety of manifestations including GI symptoms (abdominal pain, diarrhea, blood in stool, rectal prolapse), malaise, weakness, impaired cognitive / physical development, malnutrition
  • Hookworm and whipworm infestations also cause iron-deficiency anemia
    • Adult worms attach to intestinal wall to feed, causing ongoing luminal blood loss
  • Löffler’s syndrome
    • Result of Ascaris or hookworm larval transit through the lungs
    • Characterized by persistent non-productive cough, chest pain, wheezing, rales, pulmonary infiltrates on CXR and marked eosinophilia

Toxocara canis

  • Visceral toxocariasis (visceral larva migrans)
    • Larvae travel through liver / lungs / CNS causing fever, cough, enlarged liver, pneumonia
  • Ocular toxocariasis (ocular larva migrans)
    • Larvae travel to the eye causing inflammation and scarring of retina, usually only one eye, irreversible vision loss


  • Taenia (intestinal)
    • Ingestion of eggs results in intestinal infection
    • Usually asymptomatic, but heavier infections may result in GI upset, anemia, anorexia, diarrhea
  • Diphyllobothrium
    • Usually asymptomatic, may have GI symptoms
    • Rarely, migrating proglottids can cause cholangitis, cholecystitis, or intestinal obstruction
    • Competes for absorption of vitamin B12, causes pernicious anemia


  • Larvae travel from small intestine via bloodstream to multiple sites
  • Liver is target organ in ⅔ of cases
  • Less than 10% of patients have brain involvement (seizures, focal neurologic signs)
  • Pulmonary involvement also possible (cough, expectoration of sand-like material, hemoptysis, chest pain, anaphylactoid reaction from leaking cyst, mass effect from expanding cyst)

Cysticercosis (Taenia larval cysts)

  • Adult worm matures in intestine, may end up anywhere in body (CNS, muscle, soft tissue, eye, heart, liver)
  • Cluster of larvae in the brain forms expanding cyst
  • Neurologic symptoms including seizures, AMS, focal neurologic deficit, or hydrocephalus

Lymphatic filiariasis

  • Larvae migrate to lymphatic vessels and mature into adults
  • Massive peripheral edema with thickening of overlying skin particularly in lower extremities and genitalia
  • Recurrent cellulitis is common


  • Adult worm migrates through subcutaneous tissues of the leg and erodes through skin
  • Rash, intense pruritus, nausea, vomiting, dyspnea, and diarrhea prior to eruption



  • Stool studies (ova and parasites)
  • CBC to identify peripheral eosinophilia or anemia (not sensitive or specific)
  • Peripheral blood smear to identify microfilariae (e.g. lymphatic filariasis)

Disease/Symptom Specific

  • Pulmonary symptoms: CXR and sputum smear (e.g. Löffler’s syndrome)
  • CNS symptoms
    • Neuroimaging (CT with contrast or MR brain) may reveal ring-enhancing lesions, calcifications, or focal enhancing lesions in neurocysticercosis
    • CSF serologies/ELISA for echinococcus, cysticercosis
  • Ultrasound or CT can localize cyst of echinococcus
  • ELISA or biopsy of affected tissue to diagnosis toxocariasis, cysticercosis
  • Identification of adult worm or microscopic larvae in cutaneous ulcer fluid can confirm dracunculiasis

Proposed Diagnostic Criteria for Cysticercosis

  1. 1 Definitive diagnosis requires 1 absolute criterion, or 2 major plus 1 minor and 1 epidemiologic criteria.
  2. 2 Probable diagnosis requires 1 major plus 2 minor criteria, or 1 major plus 1 minor plus 1 epidemiologic criteria, or 3 minor plus 1 epidemiologic criteria.
  • Absolute
    • Demonstration of parasite from biopsy
    • Cystic lesion with scolex on neuroimaging
    • Direct visualization of parasites on fundoscopic exam
  • Major
    • Lesions highly suggestive of neurocysticercosis on imaging
    • Positive ELISA for anticysticercal antibodies
    • Resolution of intracranial lesions after antihelminthic therapy
    • Spontaneous resolution of single enhancing lesions
  • Minor
    • Lesions compatible with neurocysticercosis on imaging
    • Clinical symptoms suggestive of neurocysticercosis
    • Positive ELISA for antibodies in CSF
    • Cysticercosis outside of the nervous system
  • Epidemiologic
    • Recent travel to endemic area
    • Residence in endemic area
    • Household contact with Taenia solium infection

Clinical Management

Soil-transmitted helminthes

  • Ascaris: albendazole 400 mg x 1 dose OR mebendazole 100 mg BID x 3 days (both high efficacy)
  • Whipworm (Trichuris): albendazole 400 mg x 1 dose
    • Historically treated with albendazole or mebendazole, but monotherapy has low efficacy against Trichuris especially in heavy infections; higher cure rate achieved with oxantel pamoate-albendazole combination compared to any monotherapy in recent RCT (Speich, et al. NEJM 2014; 370:610-620)
  • Hookworm: albendazole 400 mg x 1 dose (high efficacy) OR mebendazole 500 mg x 1 dose (low to moderate efficacy)
  • Iron supplements in anemia

Toxocariasis (visceral larva migrans)

  • Diethylcarbamazine 6 mg/kg/day divided TID x 7-10 days OR mebendazole 100-200 mg BID x 5 days OR albendazole 400 mg BID x 3-5 days


  • Diphyllobothrium
    • Praziquantel 5-10 mg/kg x 1 dose
    • Replete vitamin B12 if patient has megaloblastic anemia
  • Echinococcus:
    • Tissue stage/hydatid disease: albendazole 400 mg BID x 28 days, repeat as needed every 2 weeks x 3 cycles
    • Do not aspirate cysts (risk of seeding disease or anaphylactoid reaction from spillage of hydatid sand which contains antigenic proteins)
    • Surgical resection of cysts

Cysticercosis (Taenia)

  • Neurocysticercosis
    • Antiepileptic therapy is first-line treatment
    • Treat active disease with caution. Antihelminthic therapy may cause increased inflammation, leading to further tissue damage especially with ocular or spinal involvement
    • Ophthalmologic exam before treatment
    • Steroids before antihelminthic therapy
    • Albendazole 400 mg BID x 8-30 days
    • Neurosurgery consult for symptomatic disease (acute obstructive hydrocephalus may occur)
  • Intestinal stage
    • Praziquantel 5-10 mg/kg x 1 dose

Lymphatic filariasis

  • Diethylcarbamazine:
    • Day 1: 50 mg PO
    • Day 2: 50 mg TID
    • Day 3: 100 mg TID
    • Days 4-21: 6 mg/kg/day divided TID
  • Combined treatment with diethylcarbamazine/albendazole or ivermectin/albendazole may be more effective
  • Meticulous skin care to prevent superinfection/cellulitis
  • Surgical management of scrotal elephantiasis and chronic lymphatic obstruction


  • Metronidazole 750 mg TID x 5-10 days OR thiabendazole 50-75 mg/day divided BID x 3 days
  • Must also extract adult worm from skin
  • Patients with active skin lesions should stay out of potable water

See Also

External Links


  1. "Chapter 133 - Parasitic Infections." Rosen's Emergency Medicine: Concepts and Clinical Practice. Ed. John A. Marx, Robert S. Hockberger, and Ron M. Walls. Philadelphia, PA: Mosby Elsevier, 2014. 1768-784.
  2. "The 17 Neglected Tropical Diseases." World Health Organization. http://www.who.int/neglected_diseases/diseases/en/. Web. 11 Aug. 2014.
  3. "Parasites." Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/. Web. 11 Aug. 2014.
  4. Wilcox S, Thomas S, Brown D, Nadel E. “Gastrointestinal Parasite.” The Journal of Emergency Medicine, 2007; 33(3):277-280
  5. Del Brutto OH, Rajshekhar V, White A, et al. “Proposed diagnostic criteria for neurocysticercosis.” Neurology, 2001; 57:177-183.
  6. Del Brutto OH. “Diagnostic criteria for neurocysticercosis, revisited.” Pathogens and Global Health, 2012; 106(5):299-304.
  7. Speich B, Ame S, et al. "Oxantel Pamoate–Albendazole for Trichuris Trichiura Infection." New England Journal of Medicine, 2014; 370: 610-620.