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

Types:

• 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)

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)

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

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

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 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

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

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

Tapeworm

• 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

Dracunculiasis

• 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

Sources

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.