---

Ascariasis - Complete Microbiology Notes for University Examinations

---

1. Classification & Taxonomy

• A. suum (pig roundworm) is nearly identical morphologically and can infect humans; it is associated with swine farmers and use of pig manure as fertilizer.

---

2. Morphology

Adult Worm

• Largest nematode infecting the human intestinal tract
• Female: 20-35 cm in length, up to 6 mm in diameter; straight tail
• Male: Smaller; ventrally curved (coiled) tail - key distinguishing feature
• Color: Pinkish/yellowish-white in life; reddish-orange when freshly expelled
• Three prominent lips at the anterior end (a hallmark of ascarid worms)
• Adult worms do not attach to the mucosa; they maintain position by constant motion

Eggs (Diagnostic Stage)

Exam tip: The thick outer mamillated (bumpy, albuminous) coat stained golden-brown by bile is a classic and highly testable egg feature.

---

3. Life Cycle

Step-by-Step Life Cycle

• Infective stage: embryonated egg containing a 2nd-stage larva
• Route: Feco-oral - ingestion of embryonated eggs via contaminated food, water, or soil (geophagia in children)
• Humans are the only definitive host

• Outer shell dissolved by gastric acid in the stomach
• Larvae released into the small intestine

• Larvae penetrate the duodenal/intestinal wall
• Enter the portal circulation → carried to the liver
• Travel via the heart → enter the pulmonary circulation
• Larvae penetrate the alveolar capillary bed and enter alveoli
• Remain in lungs for approximately 10-14 days, growing and molting

• Larvae ascend the bronchial tree via ciliary action
• Reach the epiglottis - coughed up and swallowed
• Return to the small intestine (primarily jejunum)
• Develop into adult male and female worms

• Adult development complete: 9-11 weeks after initial egg ingestion (60-75 days total for egg to appear in feces)
• Female produces over 200,000 eggs per day
• Adult worms survive approximately 18 months in the host
• Unfertilized eggs can be produced by females in the absence of males

• Passed eggs are unembryonated at time of excretion
• Require warm, moist, shady soil for embryonation
• Become infective in 2-4 weeks (some sources say 2 weeks in optimal conditions, 4-6 weeks typically)
• Eggs are extremely hardy: resist extreme temperatures, desiccation; viable in soil for up to 15 years

Key distinction: There is NO intermediate host in the A. lumbricoides life cycle. Humans are both the definitive host and the route of transmission. Autoinfection does NOT occur (unlike Strongyloides stercoralis).

---

4. Epidemiology

• Eggs can remain viable in contaminated soil for 3 years or more (some sources cite up to 15 years)
• In endemic areas, transmission is often seasonal (e.g., Arabian Peninsula - rainy season triggers outbreaks)

---

5. Pathogenesis & Pathology

Phase 1: Pulmonary (Larval Migration)

• Larvae cause physical disruption of alveolar walls
• Hypersensitivity reaction to secreted larval antigens
• More severe on re-exposure (sensitized individuals)
• Results in: Loeffler syndrome (see Clinical Manifestations)
• Accompanied by peripheral eosinophilia (hallmark of tissue-invasive helminths)

Phase 2: Intestinal (Adult Worm)

• Adult worms compete for host nutrition (protein, carbohydrate, vitamins)
• In children: growth retardation, malnutrition, impaired cognitive development
• Heavy worm burdens → tangled bolus → intestinal obstruction (more common in children due to smaller bowel lumen)
• Worms do NOT secrete anticoagulants; they do NOT cause blood-loss anemia (unlike hookworm)

Ectopic Migration (Dangerous Complications)

• Fever
• Inappropriate drug use (drugs other than anti-helmintics)
• Some anesthetics
• Mixed infections

• Common bile duct - biliary colic, obstructive jaundice, cholangitis
• Pancreatic duct - pancreatitis
• Liver - recurrent pyogenic cholangiohepatitis, hepatic abscess
• Appendix - appendicitis
• Stomach - rarely, gastric outlet obstruction
• Perforation of the intestinal wall → peritonitis with secondary bacterial infection (e.g., Klebsiella pneumoniae)

Exam tip: Before elective surgery under anesthesia in endemic areas, anthelmintics are routinely given to prevent anesthetic-triggered worm migration.

---

6. Clinical Manifestations

A. Pulmonary Phase (Loeffler Syndrome)

• Occurs ~1-2 weeks after heavy ingestion of eggs
• Wheezing, dyspnea, paroxysmal non-productive cough
• High fever - may last 2-3 weeks then resolve spontaneously
• Urticarial rash, angioedema
• Abdominal pain, vomiting (may coincide)
• CXR: bilateral diffuse mottled (migratory) pulmonary infiltrates
• Peripheral eosinophilia (key laboratory finding)
• More common in areas with seasonal transmission (re-exposure phenomenon)

B. Intestinal Phase

C. Ectopic / Complicated Ascariasis

• Biliary ascariasis: RUQ pain, jaundice, cholangitis, cholecystitis
• Pancreatic ascariasis: Acute pancreatitis
• Hepatic ascariasis: Recurrent pyogenic cholangiohepatitis (classic association with Klebsiella co-infection)
• Appendiceal ascariasis: Acute appendicitis
• Intestinal perforation: Peritonitis

---

7. Diagnosis

1. Stool Microscopy (Gold Standard)

• Ova and parasite (O&P) examination of fresh stool
• Fertilized eggs highly characteristic - identify by mamillated outer coat
• Female produces 200,000 eggs/day: even a single worm is likely detectable
• Quantitative assessment:
  • <20 eggs per slide (2 mg feces) = light infection

  • 100 eggs per slide = heavy infection

• Unfertilized eggs may be missed if only fertilized eggs are expected

2. Macroscopic / Clinical

• Recovery of adult worms passed in feces or vomited
• Worms may be visible in stool with naked eye

3. Imaging

• Ultrasound / X-ray / CT: Can detect adult worms as filling defects ("double-tube sign" in bile ducts)
• Chest X-ray: Loeffler syndrome - bilateral transient eosinophilic infiltrates (during larval migration)

4. Serology / Other

• Not routinely used; eosinophilia on CBC is a supportive finding (especially during larval migration phase)
• ELISA-based serological tests exist but are not standard

Exam tip: During the pulmonary (larval migration) phase, stool examination will be negative for eggs (too early - prepatent period). Eosinophilia + pulmonary symptoms + travel history should raise suspicion even with negative stool.

---

8. Treatment

Drugs of Choice

Important Treatment Note

• In patients with mixed infections (Ascaris + other helminths + Giardia + Entamoeba), treat ascariasis FIRST
• Rationale: Treating other organisms first may cause worm migration, intestinal perforation, or biliary obstruction

---

9. Prevention & Control

• Eggs are resistant to chlorination at normal concentrations - chemical disinfection alone is insufficient
• Reinfection is very common after treatment without environmental remediation

---

10. Key Distinguishing Features (Exam Comparison Table)

---

11. High-Yield Exam Summary

---

12. Quick Mnemonics

• "Ascaris = A Serious Giant" - it is the largest intestinal nematode
• "LAMP" for Loeffler syndrome features: Larvae in lungs, Asthma-like cough, Mottled CXR infiltrates, Peripaeral eosinophilia
• "MAD PIPE" for treatment alternatives: Mebendazole, Albendazole, Drug of choice - Pyrantel, Ivermectin, Piperazine, Effective alternatives
• "BBC" for ectopic complications: Biliary, Biliary pancreatic, Colonic obstruction

---