Ascaris lumbricoides is a large parasitic roundworm that causes Ascariasis, the most common human parasitic worm infection globally. An estimated 807 million to 1.2 billion people are infected worldwide, primarily in tropical and subtropical regions where sanitation is poor. This infection is classified as a soil-transmitted helminthiasis, as its life cycle involves eggs developing in the soil. While many individuals with a light worm burden may not experience symptoms, the infection can lead to severe complications affecting the lungs and intestines.
How the Infection Spreads
Infection begins with the ingestion of embryonated eggs, typically through the fecal-oral route. These microscopic, infective eggs are commonly found in soil contaminated by human feces, on raw produce, or in contaminated water.
Once swallowed, the eggs hatch into larvae in the small intestine, penetrate the intestinal wall, and enter the circulatory system. The larvae travel through the liver and heart, eventually reaching the lungs.
After 10 to 14 days in the lungs, the larvae migrate up the respiratory tract, are coughed up, and then swallowed again. This returns them to the small intestine, where they mature into adult worms.
Female adult worms can produce approximately 200,000 eggs per day. These eggs are passed out in the stool, where they must embryonate in warm, moist soil for several weeks before becoming infective to a new host.
Physical Signs of Ascariasis
Symptoms of ascariasis are related to the parasite’s movement through the body, presenting in two phases: pulmonary and intestinal. Many light infections are asymptomatic, but symptoms become more pronounced with a higher worm burden. The earliest phase, caused by larvae migrating through the lungs, occurs about one to two weeks after initial infection.
Pulmonary Phase (Larval Migration)
During larval migration through the lungs, transient respiratory symptoms may develop, often similar to asthma or pneumonia. These signs include a persistent dry cough, shortness of breath, and wheezing. In some cases, the migrating larvae cause an acute inflammatory reaction known as Löffler syndrome. This syndrome is a temporary form of eosinophilic pneumonia, characterized by an increased number of eosinophils in the lung tissue.
Intestinal Phase (Adult Worms)
The later phase involves the adult worms living in the small intestine, which may cause vague abdominal discomfort, nausea, and occasional vomiting. In children, even moderate infections can interfere with nutrient absorption and appetite, potentially leading to malnutrition and stunted growth. Heavy infections significantly increase the risk of more serious gastrointestinal problems.
A dense mass of adult worms can mechanically block the passage of food, causing an intestinal obstruction, which is a medical emergency. Adult worms may also migrate away from the small intestine, potentially moving into the appendix, bile duct, or pancreatic duct. Migration into these ducts can cause severe abdominal pain, fever, and complications like biliary colic or pancreatitis.
Diagnosis and Treatment Protocols
Diagnosing ascariasis typically involves laboratory analysis of a stool sample to look for the parasite’s eggs. The standard method is a microscopic examination for ova and parasites, which confirms the presence of the infection. However, this method is only successful once the adult female worms have matured and begun laying eggs, which takes approximately 60 to 70 days after initial infection.
If a person has only male worms, or if the larvae are still in the migratory pulmonary phase, eggs will not be present in the stool. In cases of severe complications, such as a suspected intestinal blockage, imaging tests are often employed. An X-ray of the abdomen may reveal a tangled mass of worms, and an ultrasound or CT scan can help locate worms that have migrated into the liver or pancreas ducts.
Once ascariasis is confirmed, the standard approach is treatment with highly effective anti-parasitic medications that kill the adult worms. The most commonly used drug classes are the benzimidazoles, including Albendazole and Mebendazole. Albendazole is often given as a single 400 mg oral dose, while Mebendazole can be a single 500 mg dose or a smaller dose taken twice daily for three days.
Single-dose therapy with either Albendazole or Mebendazole demonstrates high cure rates. Ivermectin is another effective option, also given as a single oral dose. These medications work against the adult worms in the intestine, and side effects are mild, sometimes including temporary abdominal discomfort or headache.
Preventing Ascariasis
Preventing ascariasis relies primarily on improving sanitation, hygiene, and safe food practices, especially in areas where the infection is common. Since the infectious eggs thrive in soil contaminated with feces, proper disposal of human waste through improved sewage systems and latrines is fundamental to breaking the transmission cycle. Avoiding open defecation minimizes environmental contamination with the parasite’s eggs.
Personal hygiene measures are equally important in preventing the ingestion of infective eggs. Washing hands thoroughly with soap and water is necessary, particularly after using the toilet and before handling or preparing food. Children should be taught to wash their hands frequently and to avoid placing them in their mouths after playing in soil.
Food safety involves washing, peeling, or cooking all raw fruits and vegetables, especially those grown in potentially contaminated soil. The eggs are highly resistant and remain viable in soil for long periods, making these precautions necessary. Drinking safe, treated water also helps prevent the accidental ingestion of parasite eggs.