Most roundworm infections cause no obvious symptoms at all, which is part of what makes them tricky to detect. When symptoms do appear, they depend on where the worms are in your body and how many you’re carrying. The clearest sign is seeing a worm in your stool or vomit, but that only happens with heavier infections. For everyone else, the clues are subtler and easy to mistake for common stomach problems.
Early Symptoms During the Lung Stage
After you swallow roundworm eggs (typically from contaminated soil, water, or unwashed produce), the larvae don’t go straight to your intestines. They first travel through your bloodstream to your lungs, where they spend 10 to 14 days maturing. During this phase, you might experience symptoms that feel like asthma or a mild pneumonia: a dry cough (sometimes bringing up small amounts of blood), wheezing, shortness of breath, and fever. These symptoms can start within one to two weeks of exposure and usually resolve on their own as the larvae leave the lungs.
This lung phase is often the most confusing because nothing about it screams “parasites.” Many people assume they have a respiratory infection or seasonal allergies. If you’ve recently traveled to a tropical or subtropical region and develop an unexplained cough with wheezing, a roundworm infection is worth considering.
Later Symptoms in the Intestines
Once the larvae crawl up your airways, reach your throat, and get swallowed again, they settle in the small intestine and grow into adult worms. A light infection, just a few worms, often causes no noticeable symptoms. Moderate infections tend to produce vague stomach pain, nausea, diarrhea or bloody stools, and a loss of appetite. Children with chronic infections may show stunted growth from poor nutrient absorption.
Heavy infections are harder to ignore. Symptoms include severe abdominal pain, persistent constipation or vomiting, weight loss, and visible malnutrition. In the most obvious cases, you may see a worm in your stool or vomit. Adult roundworms are large, often 15 to 35 centimeters long (roughly 6 to 14 inches), pale or pinkish-white, and look like thick strands of spaghetti. If that happens, there’s no ambiguity about the diagnosis.
Pinworms: A Different Set of Clues
Not all roundworms behave the same way. Pinworms, the most common roundworm infection in the United States, cause intense itching around the anus, especially at night when female worms crawl out to lay eggs. You might also notice small, thin, white worms (about the length of a staple) on your underwear or around the anal area.
You can check for pinworms at home with a simple tape test. First thing in the morning, before showering, using the toilet, or getting dressed, press the sticky side of a piece of clear tape against the skin around the anus. This picks up any eggs the worms deposited overnight. Repeat for three mornings in a row, seal each tape sample in a plastic bag, and bring them to your doctor for examination under a microscope.
How Roundworms Are Diagnosed
The standard diagnostic test is a stool sample examined for parasite eggs, called an ova and parasite (O&P) exam. A single sample catches about 76% of infections. Submitting a second sample raises the detection rate to roughly 92%, which is why doctors often request two or three samples collected on separate days. If the first comes back negative but your symptoms persist, a repeat test is worth asking about.
Blood tests can also provide clues. Roundworm infections often trigger a rise in eosinophils, a type of white blood cell that responds to parasites. Eosinophil counts at or above 500 cells per microliter suggest a possible parasitic cause, with higher counts pointing to more significant infections. This blood finding alone doesn’t confirm roundworms specifically, but combined with your symptoms and travel history, it helps narrow things down.
In severe cases where doctors suspect a bowel blockage, imaging comes into play. X-rays can reveal dilated loops of intestine and sometimes the worms themselves, which appear as distinctive tube-like shadows within the bowel. CT scans offer more detail when X-rays aren’t conclusive, and ultrasound can identify the characteristic appearance of worms inside the intestines or bile ducts.
Conditions That Look Similar
The vague stomach pain, nausea, and diarrhea caused by roundworms overlap with dozens of other conditions: irritable bowel syndrome, food poisoning, gastritis, acid reflux, and other intestinal infections. One study documented a case where a different type of roundworm infection (from eating raw fish) was initially treated as gastroesophageal reflux disease because the symptoms, including burning in the throat, stomach pain, nausea, and a dry cough, were identical.
This overlap is exactly why stool testing matters. Symptoms alone aren’t enough to confirm or rule out roundworms. If you have persistent, unexplained digestive symptoms, particularly after traveling to areas where roundworm infections are common, a stool O&P exam is the most direct way to get a clear answer.
Who Is Most at Risk
Globally, an estimated 772 to 892 million people carry roundworm infections, with the vast majority living in tropical and subtropical regions with limited sanitation. Risk factors include living in or traveling to areas where human waste is used as fertilizer, drinking untreated water, and eating unwashed raw produce grown in contaminated soil. Children are especially vulnerable because they’re more likely to put contaminated hands or objects in their mouths.
In the United States, large roundworm infections are uncommon but do occur, particularly in rural areas of the Southeast. Pinworm infections, by contrast, are widespread regardless of geography or hygiene, especially among school-age children and their household contacts.
Warning Signs of Serious Complications
Most roundworm infections are mild and treatable. But a heavy worm burden can cause a dangerous intestinal blockage. Warning signs include worsening abdominal pain that doesn’t let up, inability to pass gas or have a bowel movement, bilious (green or yellow) vomiting, visible abdominal swelling, and increasing fatigue or dehydration. A blockage from roundworms is a medical emergency that typically requires surgery to resolve. These complications are rare but more likely in children and in people with very high worm counts.
Adult worms can also migrate into unusual places. A single worm can block the bile duct (causing jaundice and upper abdominal pain), trigger appendicitis, or even be coughed up or expelled through the nose. These events are uncommon but unmistakable when they happen.