Helminth infections

Revision as of 23:18, 6 September 2014 by AKoyfman (talk | contribs) (Differential Diagnosis)

Background

  • Approximately 2 billion people infected worldwide
  • Many are WHO-designated Neglected Tropical Diseases[1]
  • At-risk populations include impoverished, children, immigrants, tourists, HIV/AIDS patients, refugees [2]
  • Most common in subtropical and tropical areas, moist climates, poor sanitation and hygiene [3]

Transmission:

  • No direct person-to-person transmission
  • Fecal-oral transmission (ingestion of eggs in contaminated soil / vegetables / water)[3]
    • 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)

Differential Diagnosis

Types:

Roundworm

  1. Ascaris lumbricoides
  2. Toxocara canis

Whipworm

  1. Trichuris trichiura

Hookworm

  1. Necator americanus
  2. Ancylostoma duodenale

Tapeworm

  1. Diphyllobothrium latum
  2. Echinococcus granulosus

Cysticercosis

  1. Taenia solium
  2. Taenia saginata

Lymphatic filariasis

  • aka Elephantiasis
  1. Wuchereria bancrofti
  2. Brugia malayi
  3. Brugia timori)

[Dracunculiasis]]

  • aka Guinea Worm disease
  1. Dracunculus medinensis)

Onchocerciasis

  • aka River Blindness
  1. Onchocerca volvulus)

Clinical Features

History

  • 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

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[4]</ref>
  • 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

Tapeworm

  • Taenia (intestinal)[2]
    • 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[2]
    • Rarely, migrating proglottids can cause cholangitis, cholecystitis, or intestinal obstruction
    • Competes for absorption of vitamin B12, causes pernicious anemia

Diagnosis

General

  • 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[5][6]
    • 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

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 [7]
  • Hookworm: albendazole 400 mg x 1 dose (high efficacy) OR mebendazole 500 mg x 1 dose (low to moderate efficacy)
  • Iron supplements in anemia

See Also

External Links

Sources

  1. The 17 Neglected Tropical Diseases." World Health Organization. http://www.who.int/neglected_diseases/diseases/en/. Web. 11 Aug. 2014.
  2. 2.0 2.1 2.2 "Parasites." Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/. Web. 11 Aug. 2014.
  3. 3.0 3.1 "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.
  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.