Parasitic infections affect many Americans each year, yet most people remain unaware because of how easily the symptoms can be mistaken for other common health problems. From intestinal worms to microscopic organisms, these parasites can take up residence in the body and cause a range of symptoms that develop gradually or persist longer than other conditions. While a diagnosis from a doctor is necessary to accurately identify the parasite, there are a number of signs that can help you determine when to seek medical advice.

Common Parasites That Can Affect Humans

While parasitic infections are less common in the United States compared to developing countries with limited access to clean water and sanitation, they still occur regularly in American communities. The relative rarity can work against patients, as both individuals and healthcare providers may overlook parasites when evaluating digestive symptoms or unexplained health issues. Many people dismiss the possibility entirely, assuming parasites only affect travelers to tropical regions or areas with poor hygiene standards.

The parasites that do cause infections in the U.S. fall into three main categories based on their size and complexity. Intestinal worms are large enough to see with the naked eye and often cause obvious digestive symptoms. Protozoa are microscopic single-celled organisms that typically cause severe diarrheal illness. External parasites like scabies affect the skin rather than internal organs but can cause significant discomfort and spread easily between people.

Intestinal Worms (Helminths)

    • Tapeworms: These flat, segmented worms can grow several feet long in the intestines. Humans typically become infected by eating undercooked meat or fish containing larvae. Symptoms may include abdominal pain, nausea, and segments of the worm visible in stool.
    • Roundworms: The most common intestinal worm infection worldwide. These worms can cause abdominal pain, coughing (when larvae migrate through lungs), and in severe cases, intestinal blockage. Transmission occurs through contaminated soil or food.
    • Pinworms: Small worms that cause intense anal itching, especially at night when females lay eggs. Common in children and easily spread through contaminated surfaces. Often the first sign is scratching that disrupts sleep.
    • Hookworms: These worms attach to the intestinal wall and feed on blood, potentially causing iron deficiency anemia. Initial infection may cause a characteristic rash where larvae penetrate the skin, typically through bare feet in contaminated soil.
    • Whipworms: Cause symptoms ranging from mild digestive discomfort to severe bloody diarrhea and abdominal pain. Infection occurs through ingesting eggs from contaminated food, water, or surfaces.

    Protozoa (Single-Celled Parasites)

      • Giardia: A common cause of waterborne illness that causes severe diarrhea, bloating, and gas. Often contracted from contaminated drinking water or recreational water sources like lakes and streams.
      • Cryptosporidium: Causes watery diarrhea that can last for weeks, particularly dangerous for people with weakened immune systems. Highly resistant to chlorine, making it a persistent problem in water supplies.1

      Signs of a Possible Parasitic Infection

      One of the biggest challenges with diagnosing a parasitic infection lies not in the symptoms themselves, but in recognizing when those symptoms might indicate something beyond the usual suspects like food poisoning or irritable bowel syndrome. Most people experience digestive problems at some point, but certain patterns and circumstances make parasites a more likely culprit than others.

      Digestive issues from common causes like viral infections or food poisoning typically resolve within a few days to a week with basic care. Parasitic infections, however, tend to cause symptoms that linger or worsen over time. Diarrhea that continues for more than two weeks, especially when accompanied by weight loss, suggests something more persistent than a typical stomach bug. Similarly, abdominal pain that doesn’t respond to over-the-counter remedies or dietary changes may warrant investigation for parasites, particularly if it’s been ongoing for several weeks.

      Recent travel to areas with questionable water quality significantly increases the likelihood that digestive symptoms stem from parasitic infection. This includes not just international travel to developing countries, but also camping trips where water may have been inadequately treated, or swimming in lakes and streams. Even something as simple as eating at a restaurant with poor food handling practices can lead to exposure. The timing matters too; symptoms that develop within days to weeks of potential exposure are more suggestive of parasites than those with no clear trigger.

      While individual symptoms like diarrhea or fatigue are common to many conditions, certain combinations are more characteristic of parasitic infections. The development of iron deficiency anemia alongside digestive symptoms, for instance, suggests blood loss that could result from hookworms. Intense anal itching that worsens at night, particularly in children, strongly suggests pinworms. Seeing visible worms or worm segments in stool obviously indicates parasitic infection, though this doesn't occur with all types of parasites.2

      How Parasitic Infections Are Diagnosed

      Stool testing is one of the main ways doctors use to diagnose a parasitic infection. The “ova and parasites” test (O&P) is a comprehensive examination that involves collecting multiple stool samples over several days. Laboratory technicians examine these samples under microscopes to identify parasite eggs, larvae, cysts, or adult organisms. For some parasites like giardia and cryptosporidium, specialized antigen tests may be more sensitive than traditional microscopic examination.

      Blood tests play a supporting role, particularly when looking for signs of anemia that might suggest hookworm infection or when testing for antibodies against specific parasites. For pinworms, a “tape test” performed in the morning before bathing can capture eggs laid around the anal area overnight. The diagnostic process often requires patience since initial tests may need to be repeated depending on the suspected parasite and initial results.3

      Treatment and Prevention

      Once a parasitic infection is diagnosed, treatment typically involves specific antiparasitic medications tailored to the type of parasite identified. The approach varies significantly depending on whether the infection involves intestinal worms, protozoa, or external parasites, and most treatments require completing the full course of medication even after symptoms improve:

      • Antiparasitic medications: Doctors prescribe drugs like mebendazole, albendazole, or praziquantel to target specific types of worms, while metronidazole treats protozoan infections like giardia.
      • Supportive care: Treatment includes managing symptoms like dehydration from diarrhea, treating secondary infections, and addressing nutritional deficiencies that may have developed.
      • Iron supplementation: Patients with hookworm infections often require iron supplements to treat anemia caused by blood loss from the parasites.
      • Follow-up testing: Doctors order repeat stool samples to confirm the parasite has been eliminated, typically several weeks after treatment completion.
      • Household treatment: Family members may need treatment even without symptoms, particularly for highly contagious parasites like pinworms that spread easily between people.

      One of the most effective approaches to parasitic infections is prevention. Simple measures like thorough handwashing, cooking meat to proper temperatures, avoiding untreated water sources, and maintaining good hygiene around pets can significantly reduce exposure risk. When traveling to areas with questionable sanitation, drinking only bottled or properly treated water and avoiding raw foods helps prevent many common parasitic infections.

      Digestive Care from Cary Gastro

      Persistent digestive symptoms, whether from parasites or other causes, deserve professional evaluation and treatment. The experienced gastroenterologists at Cary Gastro specialize in diagnosing and treating a wide range of digestive disorders, providing comprehensive care that addresses both immediate symptoms and long-term digestive health. Our team uses advanced diagnostic techniques to identify the root cause of your symptoms and develop personalized treatment plans tailored to your specific needs. Contact our team today to request an appointment and take the first step toward better digestive health.




      1https://pmc.ncbi.nlm.nih.gov/articles/PMC2754014/
      2      https://www.cdc.gov/parasites/caring/index.html
      3https://www.cdc.gov/parasites/testing-diagnosis/index.html