In the global health landscape, some of the most widespread diseases are also the most neglected. Among these are infections caused by intestinal worms, which affect nearly a quarter of the world’s population, particularly children in tropical and subtropical regions. The most common of these infections is ascariasis, caused by the giant roundworm Ascaris lumbricoides. This parasitic disease is intrinsically linked to poverty and inadequate sanitation. While light infections may cause no symptoms, heavy infections can lead to serious health problems, including malnutrition, growth stunting in children, and life-threatening intestinal blockage. Understanding the life cycle of this parasite is the key to both treating the infection and, more importantly, preventing it from spreading.

Ascariasis is an intestinal infection caused by the roundworm Ascaris lumbricoides, one of the most common parasitic worms in humans. This parasite is the largest roundworm to infect the human intestine, with adult worms reaching lengths of up to 35 centimeters (14 inches), roughly the size of a standard ruler. A mature female worm can be as thick as a pencil.

Ascariasis is the most common of the “soil-transmitted helminth” (STH) infections, a group of diseases caused by parasitic worms that are transmitted through contaminated soil. The World Health Organization (WHO) estimates that over 1 billion people may be infected with STHs worldwide, with ascariasis accounting for the majority of these cases. The burden of this disease falls most heavily on children living in areas with poor sanitation and hygiene, where it can have a profound and lasting impact on their growth, nutritional status, and cognitive development. While found globally, the infection thrives in warm, moist climates.

Analogy: Think of your intestines as a pipeline. When roundworms like Ascaris live inside, it’s like having long, moving threads clogging up the flow, they take nutrients and space, and in large numbers, they can completely block the system.

You get ascariasis by accidentally swallowing infective Ascaris eggs from contaminated food, water, or soil. This usually happens in areas where human feces are used as fertilizer or where people defecate in open fields. To understand the disease, one must understand the remarkable and complex life cycle of the worm.

The life cycle of Ascaris lumbricoides proceeds in the following steps:

1. Ingestion of Eggs: A person becomes infected by swallowing microscopic, fertilized Ascaris eggs. These eggs are in soil that has been contaminated with human feces.
2. Hatching in the Intestine: The ingested eggs travel to the small intestine, where the digestive juices trigger them to hatch, releasing tiny larvae.
3. Migration to the Lungs: These microscopic larvae do not stay in the intestine. Instead, they penetrate the intestinal wall and enter the bloodstream or lymphatic system. They are then carried to the heart and pumped into the lungs.
4. Maturation in the Lungs: The larvae settle in the air sacs (alveoli) of the lungs, where they grow and mature for about 10 to 14 days. This phase can cause respiratory symptoms.
5. The Journey Back: Once they have matured sufficiently, the larvae break through the walls of the air sacs and travel up the bronchial tubes to the throat. They are then coughed and swallowed.
6. Return to the Intestine: After being swallowed, the larvae travel back down through the stomach and return to the small intestine for a second time. Here, they complete their development into adult male and female worms.
7. Reproduction: The adult worms live, mate, and thrive in the small intestine, feeding on the intestinal contents. A single adult female worm can produce approximately 200,000 eggs per day.
8. Excretion and Contamination: These eggs are mixed with the feces and are passed out of the body during a bowel movement.
9. Maturation in the Soil: The eggs passed in the feces are not immediately infectious. They must incubate in warm, moist, shaded soil for at least 2-3 weeks to develop into an infective stage. Once infected, these eggs can survive in the soil for months or even years.

This complex cycle repeats when another person ingests these mature, infective eggs from the contaminated environment.

Ascariasis is transmitted via the fecal-oral route. This means that a person gets the infection by swallowing eggs that have come from an infected person’s feces. It is important to note that the disease is not spread directly from person to person, as eggs need several weeks in the soil to become infectious.

Infection occurs when people ingest these infective eggs through one of the following pathways:

• Contact with Contaminated Soil: This is a very common route of transmission, especially for children who play in the dirt and then put their unwashed hands in their mouths.
• Consumption of Contaminated Food: Eating raw fruits or vegetables that were grown in contaminated soil and have not been carefully washed, peeled, or cooked can transmit the eggs. The use of human feces (“night soil”) as fertilizer in some agricultural areas is a major source of contamination.
• Drinking Contaminated Water: In areas with poor sanitation, water sources can become contaminated with fecal matter containing Ascaris eggs.

The risk of getting ascariasis is highest for people living in communities with inadequate sanitation infrastructure, where human waste is not properly managed and can contaminate the soil and water that people use for drinking and agriculture.

Signs and symptoms depend on the number of worms and their migration stage.

Asymptomatic Infections: In most cases, when an individual is infected with only a few worms (a light infection), they will have no symptoms at all.

When symptoms do occur, they can be divided into two phases, corresponding to the parasite’s journey through the body.

Early Phase Symptoms (Larval Migration): As the larvae migrate through the lungs (about 1-2 weeks after infection), they can cause an inflammatory reaction in some individuals. This is sometimes known as Loeffler’s syndrome. Symptoms can include:

• A persistent, dry cough
• Wheezing or shortness of breath
• A low-grade fever

These respiratory symptoms are often mild and can be mistaken for asthma or a cold. They usually resolve as the larvae leave the lungs.

Late Phase Symptoms (Adult Worms in the Intestine): Symptoms from the adult worms in the intestine typically only occur with a heavy infection or a high “worm burden.” These symptoms are particularly damaging to children.

• Vague or moderate abdominal pain and discomfort.
• Nausea and sometimes vomiting.
• Diarrhea or irregular stools.
• Malnutrition and Growth Failure: This is one of the most serious consequences of chronic, heavy infection in children. The large mass of worms consumes a significant portion of the nutrients from the food the child eats, leading to vitamin deficiencies, poor absorption of fats, protein-energy malnutrition, and stunted growth or “failure to thrive.”
• Visible Worms: Sometimes, the diagnosis becomes apparent when a person passes a large adult worm in their stool or, in rare and distressing cases, when a worm exits through the mouth or nose.

Severe Complications of Heavy Infection: In cases with a very high worm burden, a tangled mass of worms can cause life-threatening intestinal obstruction. This blockage of the small intestine is a surgical emergency that causes severe abdominal pain, vomiting, and a swollen abdomen. Additionally, individual adult worms can sometimes migrate from the intestine into other organs, blocking the bile duct (causing jaundice) or the pancreatic duct (causing pancreatitis).

Diagnosis

The definitive diagnosis of ascariasis is usually simple and straightforward.

• Stool Examination: The standard method is to have a stool sample examined under a microscope in a laboratory. The technician will look for the presence of the characteristic Ascaris eggs.
• Identification of Adult Worms: Sometimes, the diagnosis is made when an adult worm is passed from the stool, mouth, or nose and is brought to a doctor.
• Imaging: In cases where a doctor suspects a complication like intestinal or biliary obstruction, an abdominal ultrasound, X-ray, or CT scan may show a tangled mass of worms.

Treatment

Treatment of ascariasis is simple, highly effective and involves the use of anti-parasitic medications called anthelmintics.

• Medication: The drugs of choice, as recommended by the WHO, are albendazole and mebendazole. These medications are usually given as a single dose or a short course lasting one to three days. They work by killing the adult worms, which are then passed out of the body in the stool.
• Treating Complications: If a patient has severe complications like an intestinal obstruction, they will need to be hospitalized. Treatment may involve trying to clear the obstruction with medication. In many cases, endoscopic or surgical intervention is required to remove the mass of worms.

Prevention: Breaking the Cycle of Infection

The goal of prevention is to break the parasite’s life cycle. This can be achieved by combining personal hygiene and public health measures.

At the Individual and Household Level:

• Handwashing: Always wash hands thoroughly with soap and water after using the toilet, after changing a diaper, before preparing food, and before eating.
• Food Safety:
  • Carefully wash, peel, or cook all raw vegetables and fruits before eating.
  • Avoid food that may have been grown in soil fertilized with human waste.
• Water Safety: Drink only water from a safe, treated source. If you are unsure about the water quality, boil it before drinking.
• Teach Children: Educate children about the importance of handwashing and not putting unwashed hands or fingers in their mouths.

At the Community and Public Health Level:

• Effective Sanitation: The single most important prevention strategy is to end open defecation and ensure the proper, sanitary disposal of human feces. Building and using toilets and latrines is critical.
• Mass Deworming: The WHO recommends periodic, large-scale deworming programs in areas where these infections are common.

Ascariasis is the most common intestinal worm infection in the world, a silent burden that disproportionately affects the health and development of children in underprivileged communities. It is a disease born of lack of access to clean water and sanitation. While the life cycle of the Ascaris roundworm is complex and its complications can be severe, the solutions are clear and attainable. The infection is easily treated with inexpensive and effective medication. More importantly, it is preventable.

• Centers for Disease Control and Prevention (CDC). (2024). Parasites – Ascariasis. Retrieved from https://www.cdc.gov/parasites/ascariasis/index.html
• World Health Organization (WHO). (2024). Soil-transmitted helminth infections. Retrieved from https://www.who.int/news-room/fact-sheets/detail/soil-transmitted-helminth-infections
• Bethony, J., Brooker, S., Albonico, M., Geiger, S. M., Loukas, A., Diemert, D., & Hotez, P. J. (2006). Soil-transmitted helminth infections: Ascariasis, trichuriasis, and hookworm. The Lancet, 367(9521), 1521–1532. https://doi.org/10.1016/S0140-6736(06)68653-4