Ascariasis

Etiology

Ascariasis is caused by Ascaris lumbricoides, a large soil-transmitted nematode acquired through ingestion of embryonated eggs from contaminated soil, food, or water.[4][5][6] Adult female worms are larger and more robust, typically measuring 20 to 30 cm in length, whereas males are smaller (15–20 cm) and have a slender body and a ventrally curved posterior end bearing retractile copulatory spicules.[4][5] The worms are smooth and cylindrical and may appear white, yellow, or pink.

Adult females have a thicker body with a straight posterior end. The average lifespan of an adult Ascaris worm is approximately 1 year, after which the parasite dies and is expelled via the gastrointestinal tract. Because adult worms do not multiply in humans, ascariasis may resolve spontaneously in the absence of reinfection, although ongoing exposure in endemic settings frequently leads to repeated infections.[7][8][4]

Epidemiology

Ascariasis is among the most common human helminth infections worldwide and has been recognized for millennia, described in ancient medical writings, and identified in archaeological remains. However, ascariasis remains a major public health problem in many low-resource settings.[5][6] The most recent systematic review and meta-analysis estimated that the global prevalence was 11.01% (95% CI; 10.27%–11.78%), corresponding to an estimated 732 million (682–782 million) people infected in 2021, with higher prevalence in children and in rural or low-income settings, and associations with environmental conditions favorable for egg survival.[1] 

This aligns with the Centers for Disease Control and Prevention (CDC) current summary estimate that approximately 772 to 892 million people are infected globally, with the greatest burden in tropical and subtropical regions of Asia, sub-Saharan Africa, and the Americas.[CDC. About Ascariasis. 2024] Ascariasis transmission is tightly associated with poverty and inadequate sanitation because eggs passed in human feces contaminate soil, food, and water; risk is amplified where hygiene infrastructure is limited and where fecal contamination of the environment occurs, including some agricultural practices, eg, the use of human feces as fertilizer.[5][6][9][10] [WHO. Soil-Transmitted Helminth Infections. 2023]. 

Although infection is concentrated in endemic regions, travel and migration can lead to cases in nonendemic areas, maintaining clinical relevance for clinicians caring for mobile populations and returning travelers.[11] [CDC Yellow Book. Post-Travel Parasitic Disease Including Evaluation of Eosinophilia. 2025] Recent molecular epidemiology research has shown that Ascaris transmission may be highly focal even within endemic communities: a whole-genome sequencing study from Ethiopia revealed that parasite populations often cluster at the household level, with reinfections commonly occurring among close contacts.[12] These findings, along with early genomic signals suggestive of drug selection pressure, underscore the importance of targeted interventions and genomic surveillance in identifying transmission hotspots and monitoring for potential emergence of anthelmintic resistance.[13][11][12]

Pathophysiology

Infection occurs when a human host ingests embryonated Ascaris eggs present in stool-contaminated soil, food, or water.[8][9][11] After ingestion, eggs hatch in the duodenum, releasing larvae that penetrate the intestinal mucosa and enter the circulation via venous, arterial, or lymphatic vessels. The larvae migrate through the portal system to the liver and subsequently reach the lungs within approximately 7 to 10 days.

In the pulmonary phase, larvae penetrate the alveolar membranes and mature within the alveoli, causing transient inflammatory injury. They then ascend the bronchial tree, are expectorated, and swallowed, thereby reentering the gastrointestinal tract. Once back in the lumen of the small intestine, larvae mature into adult worms over 2 to 3 weeks.[8][9] When both male and female worms are present, copulation occurs, and an adult female can produce up to 200,000 eggs per day, which are excreted in feces.[8][9][11][14] Under favorable environmental conditions consisting of warm, moist, and shaded soil, eggs embryonate and become infective within 2 to 8 weeks and may remain viable for prolonged periods, with reports of survival ranging from months to several years (up to a decade or more), facilitating sustained transmission and reinfection in endemic areas.[8][9][15][16][4][5][17]

Histopathology

A fertilized Ascaris egg can be visualized with microscopy of a stool sample (see Image. Ascaris Ova).

History and Physical

Most individuals infected with ascariasis are asymptomatic or experience mild, nonspecific symptoms, with clinical manifestations largely determined by parasite burden and related complications.[14] Low-intensity infections may remain clinically silent and present only with long-term sequelae, eg, growth retardation and malnutrition, particularly in children. When symptoms occur, the most common gastrointestinal manifestations include abdominal pain, bloating, nausea, vomiting, anorexia, and intermittent diarrhea. During the larval migratory phase, a heavy pulmonary larval burden may result in transient eosinophilic pneumonitis (Löffler syndrome), characterized by cough, wheezing, dyspnea, fever, hemoptysis, and peripheral eosinophilia.

Severe complications are primarily related to adult worm migration, especially in the setting of high parasite loads or superinfection. Adult worms may migrate into tubular structures, eg, the biliary and pancreatic ducts, leading to biliary colic, cholecystitis, cholangitis, pancreatitis, as well as small-bowel obstruction, volvulus, appendicitis, and intussusception. Children are disproportionately affected by both morbidity and complications due to higher infection intensity and nutritional vulnerability, and may present with growth failure, malnutrition, abdominal pain, diarrhea, and nausea, making ascariasis an important contributor to pediatric disease burden in endemic regions.[4][5][18][19] 

Evaluation

Adult female Ascaris lumbricoides worms can produce up to 200,000 eggs per day, facilitating detection through stool-based diagnostics.[4][5][6] The cornerstone of diagnosis remains direct microscopic examination of stool samples for ova and parasites.[5][20] This typically involves examining 2 slides per sample to identify the characteristic large, oval, brown, trilayered eggs with a mammillated outer coat (see Image. Ascaris Ova). In endemic areas, the World Health Organization (WHO) recommends the Kato–Katz thick smear technique for both diagnosis and quantification of infection intensity at the population level.[5] However, this method has notable limitations, particularly in low-intensity infections.

A field study in Kenya demonstrated that Kato–Katz microscopy detected only 54% to 64% of Ascaris infections, missing many mild or prepatent cases. In contrast, a multiplex real-time PCR (qPCR) assay exhibited significantly higher sensitivity and served as the reference standard. Additionally, serologic testing showed that IgG1 antibodies against adult worm excretory-secretory antigens were highly specific and sensitive for active infection (AUC ≈0.83), making them a promising adjunct for surveillance in endemic areas. These findings suggest that combining qPCR for sensitive detection with IgG1 serology to assess exposure status can improve diagnostic accuracy, particularly when microscopy underestimates true prevalence.

Stool examinations may also yield false negatives during the early migratory and maturation phase—approximately the first 3 to 4 weeks post-infection—when egg excretion has not yet begun. In such cases, clinical clues become important: eosinophilia may be observed during the larval migratory phase, and larvae may be recovered in sputum during pulmonary involvement. Occasionally, adult worms may be directly visualized when passed in stool, expelled rectally, or expectorated, and rare reports describe worms expelled in urine due to aberrant migration. Imaging modalities further aid diagnosis in complicated presentations: abdominal radiographs may reveal nonspecific signs, eg, the “whirlpool” or “railway track” pattern; ultrasound and computed tomography (CT) imaging can detect adult worms in the hepatobiliary system; and endoscopic retrograde cholangiopancreatography (ERCP) can confirm diagnosis and facilitate removal in cases of biliary ascariasis.[19]

To address the limitations of manual microscopy, recent advances in artificial intelligence (AI) have shown great promise. A 2025 study evaluated deep learning models trained to recognize helminth eggs in microscopic images. These AI-powered diagnostic tools offer high accuracy, objectivity, and scalability, making them especially attractive for use in resource-limited settings.[21][22] Furthermore, WHO expert groups have explored point-of-care antigen detection using urine-based circulating cathodic antigen (POC-CCA) assays.[23] While their role in routine Ascaris diagnosis remains under investigation, they may hold potential in selected epidemiologic contexts. Taken together, these traditional and emerging diagnostic modalities—from microscopy and molecular assays to serology and AI—highlight the evolving landscape of ascariasis detection and the need for context-specific diagnostic strategies.[24][4][18][25][19][26][21]

Treatment / Management

Even mild or asymptomatic ascariasis should be treated to reduce the parasite burden and prevent complications associated with adult worm migration. However, during the early pulmonary (larval migratory ) phase, antihelminthic therapy is generally deferred, as treatment at this stage may exacerbate eosinophilic pneumonitis (Löffler syndrome) due to inflammatory responses to dying larvae. Once adult worms are established in the intestine, albendazole 400 mg orally as a single dose is the treatment of choice, with mebendazole (100 mg twice daily for 3 days or a single dose of 500 mg) and ivermectin (150–200 µg/kg as a single dose) serving as effective alternatives. Importantly, all these treatments were well tolerated and deemed safe in both children and adults, with no serious adverse events reported. However, in pregnancy, particularly during the first trimester, pyrantel pamoate (11 mg/kg, maximum 1 g, single dose) is preferred due to its favorable safety profile; piperazine may also be used when necessary.

Anthelmintic therapy targets adult worms only and is ineffective against migrating larvae; therefore, a repeat dose after 1 to 3 months is recommended in endemic settings to allow any residual larvae to mature into susceptible adults. In a randomized trial and subsequent meta-analyses, single-dose albendazole, mebendazole, and pyrantel pamoate achieved cure rates exceeding 85%, with albendazole demonstrating the highest egg-reduction rates (>98%). Alternative agents, eg, nitazoxanide and levamisole, have demonstrated efficacy but are less commonly used. Posttreatment stool reexamination at approximately 3 months is recommended to assess for persistent infection and to guide retreatment; household contacts should be screened and treated in endemic settings to limit reinfection.

In cases of intestinal obstruction, management depends on severity. Partial obstruction should be treated conservatively with bowel rest, nasogastric decompression, intravenous fluids, and antihelminthic therapy (traditionally piperazine). Complete obstruction or complications, eg, volvulus, ischemia, or perforation, require surgical or endoscopic intervention for worm extraction, with bowel resection and anastomosis reserved for necrotic segments. Following restoration of intestinal transit, antihelminthic therapy should be administered to eradicate remaining adult worms and reduce the risk of recurrence.[27][20][28][23][29][30][18][31][32](A1)

Differential Diagnosis

The clinical manifestations of ascariasis vary with parasite burden, life cycle stage, and anatomic involvement and therefore overlap with several gastrointestinal, hepatobiliary, and respiratory conditions.

Hepatobiliary and Pancreatic Disorders

Acute cholangitis, or ascending cholangitis, presents with fever, right upper quadrant pain, and jaundice, consistent with Charcot triad. Bacterial cholangitis commonly results from obstructing gallstones or strictures and is frequently associated with positive blood cultures. In contrast, imaging in ascariasis-related disease may demonstrate linear or motile filling defects within the bile ducts rather than calculi.

Cholecystitis and biliary colic from gallstone disease produce episodic or persistent right upper quadrant pain, often following meals, with ultrasound findings of gallstones and gallbladder wall thickening. In biliary ascariasis, imaging may reveal mobile echogenic tubular structures without acoustic shadowing.

Acute pancreatitis presents with epigastric pain radiating to the back and elevated pancreatic enzyme levels. Gallstones and alcohol represent the most common causes; however, migration of Ascaris into the pancreatic duct remains a recognized etiology in endemic regions and warrants consideration when imaging demonstrates ductal obstruction without stones.

Intestinal and Surgical Emergencies

The following emergent conditions may have overlapping clinical features with ascariasis:

• Appendicitis: Presents with periumbilical pain migrating to the right lower quadrant, fever, and leukocytosis. Ascariasis may mimic appendicitis due to localized inflammation or obstruction, but may be distinguished by imaging or passage of worms.
• Small bowel obstruction: A classic complication of heavy ascariasis, especially in children, caused by worm boluses. Differentiation from adhesive obstruction or hernias relies on imaging showing intraluminal filling defects or “whirlpool” patterns.
• Large bowel obstruction: Less common in ascariasis; more often caused by malignancy, volvulus, or strictures. Ascariasis-related obstruction typically involves the small intestine.

• Intussusception: Common in young children and presents with intermittent abdominal pain, vomiting, and sometimes “currant jelly” stools. Ascariasis can act as a lead point in endemic areas.

Respiratory Conditions

Asthma presents with wheezing, cough, and dyspnea that may resemble symptoms seen during the pulmonary migratory phase of ascariasis. In ascariasis, symptoms tend to be transient, accompanied by eosinophilia, and may include fever or pulmonary infiltrates consistent with Löffler syndrome. Eosinophilic pneumonitis, or Löffler syndrome, requires differentiation from asthma, pneumonia, and hypersensitivity pneumonitis. A history of exposure and the presence of peripheral eosinophilia provide important diagnostic clues.

Parasitic Infections

The following parasitic infections may also have overlapping clinical features with ascariasis:

• Hookworm infection (Ancylostoma duodenale, Necator americanus): Can cause abdominal symptoms and eosinophilia but is more commonly associated with iron-deficiency anemia rather than mechanical obstruction or biliary disease.
• Other soil-transmitted helminths (eg, Trichuris trichiura): Typically cause chronic diarrhea or rectal prolapse rather than obstruction or hepatobiliary complications.

In endemic settings or among migrants and travelers, ascariasis should be considered in patients presenting with unexplained biliary disease, bowel obstruction, eosinophilia with pulmonary symptoms, or recurrent abdominal pain, particularly in children.[4][5][18][25]

Prognosis

The prognosis of ascariasis is generally excellent with appropriate treatment, particularly in uncomplicated infections. As stated before, studies from endemic regions in Asia and sub-Saharan Africa demonstrate that single-dose albendazole (400 mg) achieves cure rates of 90% to 95%, with a progressive, substantial reduction in egg excretion over subsequent weeks in the vast majority of treated individuals. Clinical recovery is typically rapid, and mortality is rare, occurring mainly in the context of severe complications, eg, intestinal obstruction or hepatobiliary involvement.

Despite high treatment efficacy, reinfection is common in endemic areas due to persistent environmental contamination, making relocation alone insufficient without broader public health interventions. Consequently, long-term prognosis at the population level depends heavily on prevention strategies. The WHO emphasizes a multipronged approach that includes preventive chemotherapy, particularly mass drug administration (MDA) with albendazole or mebendazole targeting school-aged children and other high-risk groups, sustained improvements in water, sanitation, and hygiene (WASH) infrastructure for both household and agricultural environments, and environmental and agricultural deworming practices, including reducing the use of untreated human feces as fertilizer.[WHO. Preventive Chemotherapy to Control Soil-Transmitted Helminth Infections in At-Risk Groups. 2017]

Additional preventive measures, eg, access to clean drinking water, improved latrine coverage, avoiding contact with untreated manure, using protective footwear, and community-based health education, are critical for reducing transmission and preventing recurrence. Increasingly, socioeconomic development initiatives aimed at alleviating poverty and improving living conditions have been recognized as essential to achieving durable reductions in the burden of ascariasis. When these combined measures are implemented, ascariasis-associated morbidity, particularly growth impairment and malnutrition in children, can be substantially reduced, leading to favorable long-term outcomes at both individual and community levels.[29][18][9][23][14]

Complications

Ascariasis can lead to a wide range of complications, particularly in individuals with high parasite burden, recurrent infection, or delayed treatment, and disproportionately affects children in endemic regions.

Gastrointestinal Complications

Gastrointestinal conditions that may develop due to ascariasis include:

• Bowel obstruction: One of the most serious and well-documented complications, especially in children, caused by boluses of adult worms obstructing the small intestine. Clinical manifestations include abdominal distension, vomiting, constipation, and abdominal pain, and severe cases may progress to volvulus, ischemia, perforation, or peritonitis, requiring surgical intervention.
• Appendicitis: Migration of adult worms into the appendix may cause luminal obstruction and inflammation, mimicking or precipitating acute appendicitis.
• Bleeding per rectum: Although uncommon, mucosal irritation, ulceration, or secondary bacterial infection associated with a heavy worm burden or intestinal obstruction may result in lower gastrointestinal bleeding, particularly in children.

Hepatobiliary and Pancreatic Complications

Hepatic and pancreatic complications associated with ascariasis include:

• Hepatobiliary disease: Adult worms may migrate into the biliary tree and gallbladder, leading to biliary colic, acute cholecystitis, cholangitis, hepatic abscess, and recurrent right upper-quadrant pain. Imaging often reveals linear or motile intraductal structures, distinguishing ascariasis from gallstone disease.
• Pancreatic involvement: Migration into the pancreatic duct can cause acute pancreatitis and, in rare cases, result in pancreatic pseudocyst formation due to ductal obstruction and inflammation. Ascariasis should be considered in patients from endemic regions presenting with pancreatitis without typical risk factors.

Nutritional and Developmental Consequences

Chronic or repeated ascariasis contributes to protein–energy malnutrition, micronutrient deficiencies, impaired linear growth, and reduced cognitive development in children. Mechanisms include competition for nutrients, decreased appetite, malabsorption, and chronic intestinal inflammation. These effects are amplified in settings of poverty and food insecurity and represent a major component of the global disease burden attributed to ascariasis.

Additional Considerations

Complications demonstrate a clear dose-dependent relationship, with higher morbidity associated with heavy infections. Children are more susceptible than adults due to higher exposure rates, a smaller intestinal lumen, and greater nutritional vulnerability. Early diagnosis, appropriate treatment, and sustained public health interventions prevent many complications and reduce overall disease burden.