Soil-transmitted nematodes acquired in tropical regions: hookworm causes iron-deficiency anemia; ascariasis causes pulmonary and obstructive GI disease.
Also known as: hookworm, Ancylostoma duodenale, Necator americanus, ascariasis, Ascaris lumbricoides, soil-transmitted helminths, STH
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Risk factors
- Residence in or travel to tropical/subtropical regions with poor sanitation
- Walking barefoot on contaminated soil (hookworm)
- Ingestion of contaminated soil, food, or water (Ascaris)
- Pica or geophagia in children (Ascaris)
- Inadequate hand hygiene and waste management
- Co-existing malnutrition amplifies anemia and growth effects
Pathophysiology
Hookworm: filariform larvae penetrate skin (often interdigital spaces of bare feet) → migrate via blood to lungs → ascend trachea → swallowed → mature in small intestine where adult worms attach to mucosa and feed on blood. Each adult Ancylostoma consumes ~0.2 mL/day, Necator ~0.05 mL/day — explaining chronic iron-deficiency anemia. Ascaris: ingested eggs hatch in small bowel → larvae migrate through portal circulation to lungs → ascend trachea → swallowed → mature into large adult worms (15-35 cm) in jejunum. Adults can obstruct lumen, migrate into bile ducts, or perforate bowel.
Clinical presentation
Symptoms
- Hookworm — early: pruritic dermatitis at site of larval penetration (ground itch); pulmonary phase often mild
- Hookworm — chronic: fatigue, dyspnea on exertion, pallor, glossitis, pica, growth and cognitive delays in children
- Hookworm — heavy infection: protein-losing enteropathy, edema, hypoproteinemia
- Ascariasis — early (Loeffler syndrome): dry cough, wheezing, low-grade fever, transient pulmonary infiltrates, eosinophilia
- Ascariasis — intestinal: vague abdominal pain, intermittent diarrhea; heavy load can cause obstruction (especially in children) with vomiting, distension, ileus
- Ascariasis — biliary/pancreatic: RUQ pain, cholangitis, pancreatitis from worm migration up the ampulla
- Worms visible in stool or vomitus
Signs / physical exam
- Hookworm: pallor, koilonychia, signs of iron deficiency
- Ascariasis: abdominal distension, palpable mass in heavy infections, jaundice in biliary involvement
- Wheezing or transient crackles during pulmonary phase
- Edema with hypoalbuminemia in protein-losing enteropathy
Classic findings
Chronic iron-deficiency anemia with no apparent GI bleed in a patient from a tropical region — think hookworm. Large adult Ascaris worm passed in stool or coughed up. Pulmonary infiltrates with eosinophilia (Loeffler syndrome) during initial migration.
Differential diagnosis
- Other causes of iron-deficiency anemia (GI bleed, menstrual loss, dietary) — Endoscopy, occult blood; geography and exposure for hookworm
- Other intestinal helminths (Strongyloides, Trichuris) — O&P, eosinophilia; specific egg morphology
- Acute bacterial pneumonia versus Loeffler syndrome — Eosinophilia, exposure history, transient infiltrates that resolve
- Biliary disease (cholangitis, choledocholithiasis) versus Ascaris in biliary tree — Imaging may show worms in CBD/duct; ERCP
- Mechanical small bowel obstruction (adhesions, tumor) — Imaging; Ascaris bolus in pediatric obstruction in endemic areas
- Allergic asthma — Atopy history; transient migratory infiltrates suggest helminthic etiology
Diagnostic workup
Diagnostic criteria
Identification of eggs (or adult worms) on stool examination is definitive. Heavy infection may be quantified by egg-per-gram counts (Kato-Katz).
Labs
- Stool ovum and parasite exam — hookworm thin-shelled oval eggs; Ascaris large mammillated bile-stained eggs
- CBC: microcytic hypochromic anemia (hookworm); eosinophilia (variable, more prominent during migration)
- Iron studies: low ferritin, low transferrin saturation
- Albumin and total protein
- LFTs and lipase if biliary/pancreatic involvement suspected
Imaging
- Generally not required for diagnosis
- Chest x-ray for pulmonary phase showing migratory infiltrates
- Abdominal x-ray, ultrasound, or CT for suspected obstruction or biliary worms (Ascaris)
- ERCP for biliary ascariasis (diagnostic and therapeutic — extract worms)
Treatment
First-line
- Albendazole 400 mg PO single dose (Ascaris) or 400 mg PO daily x 3 days (heavy or hookworm)
- Mebendazole 100 mg PO BID x 3 days OR 500 mg single dose
- Hookworm: albendazole or mebendazole, plus iron replacement therapy; severe anemia may require transfusion
- Ascariasis with intestinal obstruction: nasogastric decompression, IV fluids, mebendazole or albendazole, piperazine (paralyzes worms, helps clear bolus) where available; surgery for nonresolving obstruction or perforation
- Biliary ascariasis: ERCP to extract worms; antihelminthic therapy
- Pyrantel pamoate 11 mg/kg (max 1 g) is an alternative (safe in pregnancy, single dose for many STH)
- Pregnancy: avoid albendazole and mebendazole in first trimester; pyrantel pamoate is preferred during pregnancy if treatment cannot be deferred
- WHO recommends mass drug administration of albendazole or mebendazole to school-age children in endemic areas
Second-line / adjunct
- Ivermectin 200 microg/kg has activity against Ascaris (and Strongyloides)
- Iron supplementation must continue 3-6 months after antihelminthic to replenish stores
- Combination therapy and re-treatment in heavily endemic settings or persistent infections
Complications
- Hookworm: profound iron-deficiency anemia, hypoproteinemia, growth and cognitive delays in children, adverse pregnancy outcomes
- Ascariasis: intestinal obstruction (volvulus, intussusception), biliary obstruction, pancreatitis, appendicitis, bowel perforation
- Larval pulmonary phase can cause Loeffler syndrome with severe wheezing in atopic patients
- Drug toxicity rare with short courses
PANCE pearls
- Hookworm is a leading global cause of iron-deficiency anemia in tropical regions — consider in any traveler or immigrant with unexplained iron-deficiency anemia.
- Ascariasis obstruction is a pediatric emergency in endemic areas — heavy worm burdens can fill the lumen.
- Ascaris can migrate up the ampulla into the biliary tree or pancreatic duct, causing cholangitis or pancreatitis treatable with ERCP.
- Albendazole and mebendazole are both effective for most soil-transmitted helminths; pyrantel pamoate is the safe pregnancy option.
- Iron repletion must be initiated alongside antihelminthic therapy in hookworm-related anemia.
References
- WHO 2017 — WHO Guideline: Preventive chemotherapy to control soil-transmitted helminth infections in at-risk population groups (WHO 2017)
- CDC — CDC Parasites — Hookworm and Ascariasis: clinical guidance
- ASTMH — ASTMH practice statements on soil-transmitted helminth infections
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