Description

Ascaris lumbricoides is a large parasitic nematode (roundworm), 15–40 cm in length, which infects humans via eggs found in soil.

Epidemiology

• Geographic distribution: South America, sub-Saharan Africa, China, and East Asia
• All ages may be affected; however, children are more frequent hosts owing to oral behavior and tend to have a higher worm burden.
• Ascariasis is more common where sanitation is poor and population is dense.
• Eggs are viable in the soil for more than 6 years in temperate climates.
• It is the most prevalent helminth infection in the world.
• ~1/6 of the world’s population is infected.
• 8–15% of infections are symptomatic.
  • 120–220 million cases
  • Mostly moderate and heavy worm loads

General Prevention

Infection control

• Sanitary disposal of human excrement, not using human feces as fertilizer, and hand washing has the potential to eliminate this infection.
• In communities with high transmission of Ascaris, community-wide mass drug delivery of anthelmintics is effective in controlling morbidity.

Pathophysiology

• Fertilized eggs are ingested from soil contaminated with human feces.
• Larvae hatch in the small intestine and migrate to cecum and colon.
• Larvae invade the mucosa into the venous system and travel to the portal circulation, inferior vena cava, and finally, pulmonary capillaries.
• During migration through the pulmonary vessels, an eosinophilic response is evoked.
• Larvae penetrate the alveoli, are expelled by coughing, and swallowed back (days 10–14).
• Larvae become adult worms in the small intestine (day 24).
• Female worms excrete up to 200,000 eggs per day.
• Ingestion to excretion takes 2–3 months.
• Once in soil, fertilized eggs require 2–3 weeks of incubation in soil to become infectious and restart cycle.

Etiology

Children commonly acquire this infection from playing in dirt contaminated with Ascaris eggs.

Commonly Associated Conditions

• This infection may be associated with other soil-transmitted helminths:
  • Hookworm (Necator americanus, Ancylostoma duodenale)
  • Trichuris trichiura
  • Strongyloides stercoralis
  • Toxocara canis

History

• Gastrointestinal symptoms include the following:
  • Abdominal distention
  • Pain
  • Nausea
  • Diarrhea
  • Decreased appetite
• In the chronic phase, ascariasis is associated with the following:
  • Growth stunting
  • Cognitive delays
• Severe respiratory symptoms during the pulmonary migratory stage, when larvae cause an inflammatory response (Löeffler syndrome), characterized by the following:
  • Dyspnea
  • Cough
  • Fever
  • Shifting pulmonary infiltrates
  • Eosinophilia
• Severe presentation during the intestinal phase, when symptoms are due to the presence of worms:
  • Pain
  • Obstruction (2 per 1,000)
  • Peritonitis from perforation
  • Biliary colic, hepatitis, or pancreatitis from blockages due to worms
• History of passage of large worms in the stool or vomitus is suggestive of ascariasis.
• History of wheezing may precede passage of worms by 2–3 months.

Physical Exam

• Chest: may have rales or wheezing if Ascaris larvae are in the lungs
• Abdomen
  • Distended
  • Auscultate and palpate for signs of obstruction or perforation.

Diagnostic Tests and Interpretation

Differential Diagnosis

Ascariasis should be considered in the differential diagnosis when a patient presents with pneumonia, peripheral eosinophilia, and/or intestinal obstruction in returned traveler or resident from an endemic area.

Medication (Drugs)

Surgery/Other Procedures

Surgery or endoscopic retrograde cholangiopancreatography may be required for severe intestinal or biliary tract obstruction.

Follow-Up Recommendations

• Treatment is highly effective.
• Reexamination of stool specimens 2 weeks after therapy can be considered but is not essential.
• Reinfection is common in endemic areas and has led to mass drug administration programs.

Prognosis

• Once intestinal infection is detected and treated, the prognosis is excellent.
• If obstructive or respiratory complications have occurred, the prognosis is less favorable.
• The case fatality rate in cases with complications is up to 5%, most from obstruction.

Complications

• Bronchopneumonia may be seen during the pulmonary migrational stage, producing fever, cough, dyspnea, wheeze, eosinophilia, and pulmonary infiltrates (Löeffler syndrome).
• Heavy infestations may cause abdominal pain, malabsorption, and growth failure.
• Children may experience obstruction (ileocecal), malabsorption, or intussusception.
• Perforation or migration into the appendix, biliary, or pancreatic ducts may rarely occur.
• Hepatitis, acute cholecystitis, or pancreatitis can occur. Liver abscess can occur if intrahepatic ducts are obstructed.

ICD-9

• 127.0 Ascariasis

ICD-10

• B77.9 Ascariasis, unspecified
• B77.0 Ascariasis with intestinal complications
• B77.81 Ascariasis pneumonia
• B77.89 Ascariasis with other complications

SNOMED

• 50982003 Infection by Ascaris lumbricoides (disorder)
• 1082721000119101 Pneumonia due to Ascaris (disorder)