Helminth infections
Background
- 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
Transmission:
- 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)
Differential Diagnosis
Types:
- Roundworm
- Whipworm (Trichuris trichiura)
- Hookworm
- Tapeworm
- Cysticercosis
- Lymphatic filariasis (aka Elephantiasis; Wuchereria bancrofti, Brugia malayi, and Brugia timori)
- Dracunculiasis (aka Guinea Worm disease; Dracunculus medinensis)
- Onchocerciasis (aka River Blindness; 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
- 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)
- 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
Echinococcosis
- 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 filariasis
- 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
Dracunculiasis
- Adult worm migrates through subcutaneous tissues of the leg and erodes through skin
- Rash, intense pruritus, nausea, vomiting, dyspnea, and diarrhea prior to eruption
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
- 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 (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
See Also
External Links
Sources
- "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.
- "The 17 Neglected Tropical Diseases." World Health Organization. http://www.who.int/neglected_diseases/diseases/en/. Web. 11 Aug. 2014.
- "Parasites." Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/. Web. 11 Aug. 2014.
- Wilcox S, Thomas S, Brown D, Nadel E. “Gastrointestinal Parasite.” The Journal of Emergency Medicine, 2007; 33(3):277-280
- Del Brutto OH, Rajshekhar V, White A, et al. “Proposed diagnostic criteria for neurocysticercosis.” Neurology, 2001; 57:177-183.
- Del Brutto OH. “Diagnostic criteria for neurocysticercosis, revisited.” Pathogens and Global Health, 2012; 106(5):299-304.
- Speich B, Ame S, et al. "Oxantel Pamoate–Albendazole for Trichuris Trichiura Infection." New England Journal of Medicine, 2014; 370: 610-620.