Ascaris Lumbricoides: The Stomach Worm Nobody Wants

Ascaris lumbricoides are large, pale white or pink worms that can grow up to 12 inches (31 cm) long in humans, making these some of the biggest intestinal nematodes around.

The female worms are usually larger than the males, and they're capable of producing hundreds of thousands of eggs every day. These worms have a cylindrical body, tapered at both ends, and lack any distinctive features like a head or eyes.

Unlike some worms, Ascaris lumbricoides don't have hooks or suckers to latch onto their host. Instead, they live freely in the intestines, where they absorb nutrients directly from the partially digested food of their host.

Because of their size and high reproductive capacity, adult worms living inside the human gut can cause a variety of digestive issues.

While Ascaris lumbricoides is the main species infecting humans, its close relative, Ascaris suum, primarily infects pigs. Both species are remarkably similar in structure and life cycle, and they can occasionally cross-infect between humans and pigs.

Although the pig-specific Ascaris suum isn't as common in humans, it's worth noting that these two species are closely related and can cause similar health problems.

In fact, researchers often study Ascaris suum as a model for understanding Ascaris lumbricoides infection in humans. Both species fall into the broader category of soil-transmitted helminths, which means they spread through contact with contaminated soil.

Once inside a pig or human body, they can cause intestinal ascariasis.

Now, these worms aren't exactly social butterflies (or social worms, for that matter). Adult worms live solo in the intestines of their human hosts, and they don't interact much with each other beyond reproduction.

Once inside a host, female worms release fertilized eggs that are passed out in human feces, starting the next phase of their life cycle.

While Ascaris lumbricoides itself doesn't have a social structure, the presence of the worms can have a significant impact on human communities, especially in areas with poor sanitation.

In places where raw human feces are used as fertilizer (or where open defecation is common), these worms can spread rapidly, leading to widespread ascaris infection.

These worms may not have mouths or teeth, but they are masters at absorbing nutrients.

Once in the human intestine, Ascaris lumbricoides feeds on the nutrients passing through the digestive system. Their simple digestive system allows them to absorb these nutrients directly through their skin. Because of this, large numbers of worms can lead to malnutrition in their human hosts, especially in children.

Since they don't need to hunt or scavenge for food, Ascaris lumbricoides relies entirely on the host's diet. As the host digests food, the worms take their cut, often leading to nutritional deficiencies in infected individuals.

Ascaris lumbricoides thrives in areas with contaminated soil and poor sanitation. They are most commonly found in tropical and subtropical regions of the world, where warm temperatures and high humidity create the perfect environment for the eggs to develop.

These worms are particularly widespread in parts of Africa, Asia and Latin America, where open defecation or the use of human feces as fertilizer is common.

The eggs of Ascaris lumbricoides are incredibly resilient. Once passed out of the body in human feces, the fertilized eggs can survive in the soil for months or even years, waiting for a new host to come into contact with them.

This is why the worms are considered soil-transmitted helminths; they depend on soil for part of their life cycle.

The life cycle of Ascaris lumbricoides starts when fertilized eggs are passed out of an infected person in their feces. These lumbricoides eggs can contaminate soil, water or food. When someone ingests infective eggs, the eggs hatch in the small intestine, releasing tiny larvae.

These larvae then embark on a journey through the body, traveling through the bloodstream to the lungs. Once in the lungs, they're coughed up and swallowed, returning to the intestines, where they mature into adult worms.

From here, the cycle repeats as female worms release more eggs into the environment through the host's feces.

Unhatched eggs can be either fertilized eggs or unfertilized eggs, depending on whether the female worm has mated. Unfertilized eggs won't develop into new worms, but they still exit the body through the same process.

Ascaris infection affects over a billion people worldwide, particularly in regions with poor sanitation. Because these worms spread through contaminated soil and raw human feces, improving sanitation and access to clean water is critical to controlling their spread.

Efforts to reduce ascaris infections focus on education, proper waste disposal and the use of deworming medications.

In some regions, widespread deworming campaigns have significantly reduced infection rates, particularly among children, who are most vulnerable to intestinal obstruction and malnutrition caused by these parasites.

We created this article in conjunction with AI technology, then made sure it was edited and fact-checked by a HowStuffWorks editor.