Ascariasis is the most common parasitic infection in children, caused by Ascaris lumbricoides, a roundworm that parasitizes the human small intestine. Clinical manifestations may be absent, or patients may experience recurrent peri-umbilical pain and lack of appetite. In severe cases, the condition can impair growth and development in children. Due to the ability of Ascaris to migrate and penetrate tissues, a range of complications may arise.
Etiology and Epidemiology
Ascaris lumbricoides is the largest nematode that parasitizes the human intestine. Adult worms are cylindrical in shape, sexually dimorphic, and measure approximately 15 to 35 cm in length and 0.2 to 0.6 cm in diameter. Live worms are pinkish or yellowish in color. Adult worms reside in the small intestine, with female worms producing as many as 200,000 eggs daily. The eggs are excreted in the feces and become infective within 5 to 10 days under suitable environmental conditions. After being ingested, the eggs hatch, and larvae emerge, penetrating the intestinal wall. They travel through the portal venous system to the liver, pass through the right heart, and migrate to pulmonary alveoli. From there, they move to the bronchi, trachea, and pharynx, where they are swallowed again and return to the small intestine to develop into mature worms.
During the migration process, larvae can also reach other organs via the bloodstream, potentially causing tissue damage without developing into adult worms. Adult Ascaris worms are capable of migrating and penetrating tissues, leading to conditions such as biliary ascariasis and intestinal obstruction. When worms obstruct the trachea or bronchi, asphyxiation and death may occur. They may also invade the appendix or pancreatic ducts, causing inflammation. It typically takes 60 to 75 days for female worms to begin producing eggs after infection, and female worms have a lifespan of 1 to 2 years.
Human infection serves as the primary source of transmission. Due to the high fecundity of female worms and the remarkable environmental resistance of Ascaris eggs, the eggs can survive for several months in soil and remain infective for up to 2 years at temperatures of 5–10°C. Consumption of unclean food contaminated with infective eggs or ingestion of eggs on unwashed hands is the main transmission route. Eggs can also be inhaled in dust and swallowed.
People are generally susceptible, with children having a higher incidence rate than adults.
Clinical Manifestations
Symptoms Caused by Larval Migration
Larval Migration
When larvae migrate to the lungs, they may cause Ascaris larval pneumonia or eosinophilic pneumonitis (Löffler's syndrome), presenting with symptoms such as coughing, chest tightness, blood-streaked sputum, or asthma-like symptoms. Blood eosinophilia commonly occurs, while pulmonary physical signs are minimal. Chest X-rays may show spotty, patchy, or cloud-like shadows in the lungs, which tend to change or disappear quickly. Symptoms usually resolve within 1–2 weeks.
Severe Infections
Larvae may invade organs such as the brain, liver, spleen, kidneys, thyroid gland, and eyes, leading to corresponding clinical manifestations such as seizures, hepatomegaly, abnormal liver function, retinitis, eyelid edema, and changes in urinary output.
Symptoms Caused by Adult Worms
Adult worms live in the intestine and feed on partially digested food. Clinical manifestations vary depending on the number of worms and their location. Mild cases may remain asymptomatic, while heavy infections can result in reduced appetite, excessive hunger, or pica. Common symptoms include recurrent abdominal pain centered around the umbilicus, which is relieved by massage and not severe. Some patients may experience irritability, lethargy, teeth grinding, or even allergic reactions such as urticaria and asthma due to the foreign proteins produced by the worms. Severe infections can result in malnutrition and impaired growth and development.
Complications
Biliary Ascariasis
This is the most common complication. Manifestations include paroxysmal severe colicky pain in the right upper quadrant of the abdomen, bending of the body to relieve pain, nausea, and vomiting, with the potential for bile or worms to be vomited. Abdominal examination may reveal tenderness in the right upper quadrant without obvious positive findings. Patients with secondary biliary infections may develop fever, jaundice, and elevated peripheral white blood cell counts. In rare cases, worms may migrate directly into the liver, causing bleeding, abscess formation, or worm calcification. Other complications include massive biliary hemorrhage, gallstones, gallbladder rupture, bile peritonitis, acute hemorrhagic necrotizing pancreatitis, and intestinal perforation.
Ascaris-Induced Intestinal Obstruction
This condition most commonly affects children under 10 years of age, with the highest incidence occurring in those under 2 years. Worms may aggregate and form tangles, partially or completely obstructing the intestine. This is most frequently observed in the distal ileum. Symptoms include acute onset of colicky pain centered around the umbilicus or in the right lower quadrant, vomiting, abdominal distension, hyperactive bowel sounds, visible peristaltic waves, and palpable rope-like masses. Abdominal X-rays may reveal intestinal distension with air-fluid levels.
Intestinal Perforation and Peritonitis
This condition is characterized by sudden severe colicky abdominal pain involving the entire abdomen, accompanied by nausea, vomiting, and progressive abdominal distension. Physical examination may reveal significant peritoneal irritation. Abdominal X-rays show free air under the diaphragm.
Diagnosis and Differential Diagnosis
A diagnosis of ascariasis can be confirmed based on clinical symptoms and signs, a history of expelling or vomiting Ascaris worms, or the detection of Ascaris eggs from stool smear tests. If complications are present, the condition needs to be differentiated from other acute surgical abdominal conditions. Intestinal ascariasis should be distinguished from acute gastritis and peptic ulcers, while biliary ascariasis needs to be differentiated from acute cholecystitis and acute pancreatitis. Intestinal obstruction caused by Ascaris should be differentiated from intussusception.
Treatment
Anthelmintic Therapy
Mebendazole
Mebendazole is one of the first-line drugs for treating ascariasis. It is a broad-spectrum anthelmintic agent effective against Ascaris and other parasites such as pinworms, hookworms, and whipworms. For individuals over 2 years old, the dosage for treating Ascaris is 100 mg twice daily or 200 mg as a single dose per day for 3 consecutive days. The egg negativity rate after treatment is 90%–100%. Adverse effects are mild and may include gastrointestinal discomfort, diarrhea, vomiting, headache, dizziness, rash, and fever. Mebendazole compound, which contains 100 mg mebendazole and 25 mg levamisole per tablet, can be used in similar dosages.
Piperazine Citrate
Piperazine citrate is a safe and effective drug against Ascaris and pinworm infections. The daily dosage is 150 mg/kg (maximum 3 g), taken as a single dose before bedtime for 2 consecutive days. Adverse effects are mild but large doses may cause nausea, vomiting, abdominal pain, urticaria, tremors, and ataxia. It is contraindicated in patients with impaired liver or kidney function as well as in those with epilepsy. It is recommended to avoid the drug in cases of intestinal obstruction to prevent disturbing worm activity.
Levamisole
Levamisole is a broad-spectrum anthelmintic agent with cure rates for ascariasis as high as 90%–100%. It is also effective against hookworm and pinworm infections and serves as an immune modulator by restoring cell-mediated immunity. The dosage for expelling Ascaris is 2–3 mg/kg once daily, taken as a single dose before bedtime or on an empty stomach. Adverse effects are mild but may include headache, vomiting, nausea, and abdominal pain. Rare cases of leukopenia, liver damage, and rash have also been reported. Patients with impaired liver and kidney function require caution.
Albendazole
Albendazole is a broad-spectrum antiparasitic agent. For individuals over 2 years old, the dosage for treating Ascaris is 400 mg taken as a single dose before bedtime. The cure rate is approximately 96%, and if necessary, a second dose may be given after 10 days. Adverse effects are generally mild, including dry mouth, fatigue, dizziness, headache, reduced appetite, nausea, abdominal pain, and bloating. It is used with caution in children under 2 years old.
Treatment of Complications
Biliary Ascariasis
Treatment principles include relieving spasms and pain, expelling worms, controlling infections, and correcting dehydration, acidosis, and electrolyte imbalances. Anthelmintic drugs that cause muscle paralysis in the worms are preferred. For cases unresponsive to conservative treatment, surgical intervention may be necessary.
Ascaris-Induced Intestinal Obstruction
Partial intestinal obstruction can be managed with fasting, gastrointestinal decompression, fluid replacement, spasmolytics, and analgesics. Anthelmintic treatment can be administered after pain relief. Complete intestinal obstruction warrants immediate surgical intervention.
Ascaris-Induced Appendicitis or Peritonitis
Early surgical treatment is necessary following a confirmed diagnosis.
Prevention
Health education should focus on promoting hygiene practices, ensuring food safety, and maintaining personal cleanliness. Proper fecal management and discouraging defecation in open areas are also essential. Administering preventive anthelmintic treatments to high-risk populations is a feasible strategy to reduce infection rates. However, due to the high reinfection rates associated with ascariasis, treatments should be repeated every 3–6 months.
The most effective long-term preventive measures include ensuring that human feces are treated adequately prior to use as fertilizer and providing sanitation facilities for wastewater treatment. The prognosis for ascariasis is generally favorable.