Intestinal Nematode Infections¶

Chapter 239 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Parasitic · Chapter 239

Key Clinical Points¶

Gnathostomiasis: Cutaneous swellings last ~1 week but recur intermittently; CNS involvement causes agonizing radicular pain followed by paraplegia.
Löffler's Syndrome: Hallmark of eosinophilic pneumonitis during larval migration in ascariasis; transient rounded infiltrates on chest imaging.
Larva Currens: Pathognomonic serpiginous eruption in strongyloidiasis; advances rapidly up to 10 cm/h.
Strongyloides Hyperinfection: Occurs in immunocompromised hosts (e.g., high-dose glucocorticoids, HTLV-1); characterized by disseminated larvae and high mortality.
Pinworm Diagnosis: Eggs not found in feces; diagnosis requires cellulose acetate tape applied to perianal region in the morning.
Hookworm Anemia: Major consequence of chronic infection; requires iron supplementation and deworming.
Anisakiasis: Anisakid eggs are not found in stool; diagnosis requires endoscopy or histopathology.
Strongyloides Treatment: Ivermectin is more effective than albendazole; treatment must be extended in disseminated cases.
Ascariasis Complications: Biliary obstruction, intestinal obstruction, and volvulus are risks in heavy infections.
Gnathostomiasis Prevention: Adequate cooking of fish and poultry in endemic areas prevents infection.

1. DEFINITION & OVERVIEW¶

• Definition: Intestinal nematodes are roundworms ranging in length from 1 mm to many centimeters when mature. • Prevalence: Over one billion individuals worldwide are infected with one or more species of intestinal nematode. • Risk Factors: Most common in regions with inadequate sanitation and disposal of fecal waste, particularly in the tropics and subtropics; increasing frequency among immigrants and refugees to developed countries. • Impact: Not usually fatal, but contribute to malnutrition, impaired physical and cognitive development, and diminished work capacity. • Zoonotic Potential: Humans may be infected with zoonotic nematodes (e.g., trichostrongyliasis, anisakiasis).

2. EPIDEMIOLOGY¶

• Transmission: Fecally contaminated soil, often due to untreated sewage or human feces used as fertilizer. • Risk Group: Children are most commonly affected due to poor oral hygiene. • Global Prevalence (Millions): ◦ Ascariasis: 730 million ◦ Hookworm: 440 million ◦ Strongyloides: 100 million ◦ Whipworm: 465 million ◦ Pinworm: 200 million • Endemicity: S. stercoralis is endemic in Southeast Asia, sub-Saharan Africa, and Brazil; found in US immigrants/refugees from these regions.

3. ETIOLOGY & PATHOPHYYSOLOGY¶

Life Cycles by Species¶

• Ascariasis: Eggs → infective larvae in soil (weeks) → ingestion → larval migration to lungs → intestinal maturation. ◦ Adult worms produce 200,000 eggs/day; prepatent period: 2–3 months. • Hookworm: Skin penetration by filariform larvae → pulmonary migration → intestinal attachment → blood feeding. ◦ Causes iron deficiency anemia; prepatent period: 6–8 weeks. • Strongyloides stercoralis: Autoinfection cycle allows persistent infection without re-exposure; free1living phase in soil enables survival without hosts. ◦ Filariform larvae penetrate skin/mucosa → pulmonary migration → intestinal maturation. • Trichuris: Eggs → soil development → ingestion → intestinal maturation. • Enterobius: Perianal egg-laying → autoinfection via scratching. • Anisakis/Capillaria: Zoonotic transmission through raw fish consumption.

Key Parasite Characteristics (Table 239-1)¶

• Ascaris lumbricoides: Size 15–40 cm; location: small intestine; pulmonary passage: 60–75 μm; Treatment: Mebendazole, Albendazole, Ivermectin, Moxidectin, Pyrantel pamoate. • Hookworm (Necator/Ancylostoma): Size 7–13 mm; location: jejunal mucosa; pulmonary passage: 40–100 μm; Treatment: Mebendazole, Albendazole. • Strongyloides stercoralis: Size 1–2 mm; location: small intestinal mucosa; pulmonary passage: 25–30 μm; Treatment: Ivermectin, Albendazole. • Trichuris trichiura: Size 30–50 mm; location: cecum/colonic mucosa; pulmonary passage: 70–90 μm; Treatment: Mebendazole, Albendazole, Ivermectin. • Enterobius vermicularis: Size 1–2 mm; location: cecum/appendix; Treatment: Mebendazole, Pyrantel pamoate.

4. CLINICAL FEATURES¶

Ascariasis¶

• Löffler's Syndrome: Transient pulmonary infiltrates with eosinophilia (eosinophilic pneumonitis). • Obstruction: Biliary obstruction (mimics cholecystitis) or intestinal obstruction (common in children).

Hookworm¶

• Anemia: Chronic iron-deficiency anemia with fatigue, weakness, and dyspnea. • Cutaneous: 'Ground itch' rash at skin penetration site.

Strongyloidiasis¶

• Larva currens: Pruritic serpiginous eruption advancing 10 cm/h. • Abdominal Pain: Resembles peptic ulcer disease. • Hyperinfection Syndrome: Occurs in immunocompromised hosts (e.g., high-dose glucocorticoids, HTLV-1); leads to colitis, polymicrobial sepsis, pneumonitis, or meningitis.

Trichuriasis¶

• Symptoms: Gastrointestinal symptoms; rectal prolapse or anemia in heavy infection.

Enterobiosis¶

• Symptom: Perianal pruritus; rare genital involvement.

Gnathostomiasis¶

• Cutaneous: Migratory swellings (last ~1 week). • CNS: Eosinophilic meningitis, radicular pain, and potential paraplegia. • Ocular: Inflammation.

5. DIFFERENTIAL DIAGNOSIS¶

• Gnathostomiasis: Cutaneous swellings + eosinophilia + geographic history. • Ascariasis: Biliary obstruction vs. cholecystitis; intestinal obstruction vs. appendicitis. • Strongyloidiasis: Larva currens vs. urticaria; abdominal pain vs. peptic ulcer disease. • Trichuriasis: Bloody diarrhea vs. inflammatory bowel disease. • Anisakiasis: Acute abdomen vs. peritonitis; eosinophilic granuloma vs. Crohn's disease. • Key Diagnostic Distinctions: ◦ Ascariasis: Adult worms visible on imaging. ◦ Hookworm: Hypochromic microcytic anemia with eosinophilia. ◦ Strongyloides: Eosinophilia fluctuates (absent in severe cases). ◦ Trichuriasis: Lemon-shaped T. trichiura eggs in stool. ◦ Enterobius: Pinworm eggs not found in feces.

6. INVESTIGATIONS & DIAGNOSIS¶

Ascariasis: Stool microscopy for 65 × 45 μm Ascaris eggs.
Hookworm: Fecal examination for 40 × 60 μm hookworm eggs; larvae in old stool.
Strongyloides: • Stool concentration techniques. • PCR for species identification. • Sputum (in hyperinfection). • Serology.
Trichuriasis: Microscopy for 50 × 20 μm T. trichiura eggs.
Enterobius: Cellulose acetate tape test for perianal region (performed in the morning).
Anisakiasis: Endoscopy to visualize larvae or histopathology.

7. MANAGEMENT & TREATMENT¶

Ascariasis: • Albendazole (400 mg × 3 days) or Mebendazole. • Alternative options: Ivermectin, Moxidectin, Pyrantel pamoate.
Hookworm: • Albendazole (400 mg × 1 day) or Mebendazole.
Strongyloides: • Ivermectin (200 μg/kg × 1–2 doses) [Preferred over albendazole]. • Albendazole for disseminated disease.
Trichuriasis: • Mebendazole (100 mg × 3 days), Albendazole, or Ivermectin.
Enterobius: • Mebendazole (100 mg × 1 day) or Pyrantel pamoate.
Anisakiasis: • Endoscopic removal of larvae.

8. PROGNOSIS & COMPLICATIONS¶

• Ascariasis: Biliary/intestinal obstruction, volvulus. • Hookworm: Chronic anemia leading to growth retardation in children. • Strongyloides: Hyperinfection syndrome (50–80% mortality in immunocompromised hosts). • Trichuriasis: Rectal prolapse in severe pediatric infections. • Anisakiasis: Acute abdomen requiring urgent endoscopy.

KEY PEARLS & HIGH-YIELD POINTS¶

• Larva currens is pathognomonic for strongyloidiasis (serpiginous, 10 cm/h). • Strongyloides hyperinfection is a medical emergency in immunocompromised patients. • Pinworm eggs are never found in stool; use tape test. • Anisakid eggs are not found in stool; requires endoscopy. • Gnathostomiasis can cause severe CNS involvement (radicular pain/paraplegia).

Reference Tables¶

TABLE 239-1 Major Human Intestinal Parasitic Nematodes FEATURE Global prevalence in humans (millions) Endemic areas…¶

Harrison's 22e, p.1815

FEATURE	PARASITIC NEMATODE
	ASCARIS LUMBRICOIDES (ROUNDWORM)	NECATOR AMERICANUS, ANCYLOSTOMA DUODENALE, ANCYLOSTOMA CEYLANICUM (HOOKWORM)	STRONGYLOIDES STERCORALIS	TRICHURIS TRICHIURA (WHIPWORM)	ENTEROBIUS VERMICULARIS (PINWORM)
Global prevalence in humans (millions)	730	440	100	465	200
	Hot, humid regions	Hot, humid regions	Hot and warm, humid regions	Hot, humid regions
Infective stage	Egg	Filariform larva	Filariform larva	Egg	Egg
	Oral	Percutaneous	Percutaneous or autoinfective	Oral
Gastrointestinal location of worms	Small intestine	Jejunal mucosa	Small intestinal, mucosa	Cecum, colonic mucosa	Cecum, appendix
	15–40 cm	7–13 mm	1–2 mm	30–50 mm
Pulmonary passage of larvae	Yes	Yes	Yes	No	No
	60–75	40–100	25–30	70–90
Longevity	1 year	N. americanus: 2–5 years A. duodenale: 6–8 years A. ceylanicum: 6–8 yearsb	Decades (due to autoinfection)	5 years	2 months
	240,000	N. americanus: 9000–10,000 A. duodenale: 10,000–28,000 A. ceylanicum: 5,000–15,000	5000–10,000	3000–7000
Principal symptoms	Gastrointestinal symptoms; rarely, biliary obstruction or, in heavy infections, gastrointestinal obstruction	Iron-deficiency anemia in moderate and heavy infections	Gastrointestinal symptoms; malabsorption or sepsis in hyperinfection	Gastrointestinal symptoms, rectal prolapse, or anemia in heavy infection	Perianal pruritus
	Eggs in stool	Eggs in fresh stool, larvae in old stool	Larvae in stool or duodenal aspirate; sputum in hyperinfection; serology	Eggs in stool
Treatment	Mebendazole Albendazole Ivermectin Moxidectin Pyrantel pamoate	Mebendazole Albendazole	Ivermectin Albendazole	Mebendazole Albendazole Ivermectin	Mebendazole Albendazole Pyrantel pamoate