Intestinal worms (helminths) are infectious parasites that typically inhabit the gastrointestinal tract and lead to gastrointestinal symptoms. They are often spread via oral-fecal contamination. The most common types of worms include tapeworms, round worms (nematodes), hook worms, and pinworms. These parasites typically affect individuals from high-risk or endemic areas such as India, South America, and Africa. Travelers to these regions are also at increased risk of disease.
Most parasitic infections are asymptomatic; however, individuals can experience non-specific gastrointestinal symptoms such as abdominal discomfort, nausea, vomiting, and diarrhea. Severe cases may be complicated by hepatobiliary or liver disease, rectal prolapse, and malnutrition.
Intestinal worms are caused by a variety of parasitic species including:
- Ascaris lumbricoides (giant roundworm)
- Tapeworms (cestodes) including Taenia saginata and Diphyllobothrium latum.
- Hookworms including Ancylostoma duodenale and Necator americanus
The majority of these organisms are transmitted by the fecal-oral route. This means that infected individuals soil their hands and contaminate food that is ingested by other individuals.
For example, Ascaris lumbricoides (giant roundworm) is transmitted by oral ingestion of eggs through contaminated food or water. The eggs subsequently hatch in the intestines and release larvae that enter the lungs through the blood circulation. In the lungs, the larvae eventually make their way up the respiratory tract and then become swallowed. Next, the larvae enter the small intestinal again, where they grow into mature adults that may be up to 35 cm in length. Eggs of these mature larvae are subsequently passed into the stool.
Intestinal tapeworms (cestodes) include Taenia saginata and Diphyllobothrium latum. Taenia saginata most often occurs in parts of Europe and Asia and is usually transmitted via undercooked beef. Diphyllobothrium latum is seen in northern Europe and Japan and is usually transmitted by consumption of raw freshwater fish.
Hookworms such as Ancylostoma duodenale and Necator americanus are typically spread through a different mechanism. As opposed to the fecal-oral route, the larvae of these parasites penetrate the skin and eventually make their way to the gastrointestinal tract through the blood stream.
Intestinal worms are uncommon in the United States – however, endemic areas in parts of the Mediterranean, South America, Africa, and Asia have a high prevalence of disease. The condition may require referral to an infectious disease and gastroenterology specialist if first-line treatment was unsuccessful.
Worldwide, Ascaris lumbricoides infection affects about 800 million people. Most of these individuals are from Asia, Africa, and South America. Infection rates are up to 95% in some of these populations. Ascariasis is most often seen in children age 2-10. The disease is less likely in individuals age >15.
Symptoms of intestinal worm infection frequently depend on the specific organism responsible for infection and the stage of infection.
Pinworm infection (Enterobius vermicularis) is often asymptomatic but may result in anal itching at night. Rarely, patients experience gastrointestinal symptoms including abdominal discomfort, nausea, and vomiting. Trichuris trichiura (whipworm) infection is usually asymptomatic but severe infection can lead to rectal prolapse. Patients may experience loose stools with mucous and blood, particularly at nighttime.
Ascaris lumbricoides is also frequently asymptomatic but can cause intestinal obstruction, hepatobiliary disease, and symptoms of pancreatic obstruction. Early on, individuals may experience respiratory symptoms due to larval migration in the lungs.
Diphyllobothrium latum is frequently associated with megaloblastic anemia due to vitamin B12 deficiency. Anemia often leads to fatigue, low energy, and exertional shortness of breath.
The diagnosis of intestinal worms is suggested based on symptoms, history, and physical examination, but typically confirmed with laboratory studies. The condition is usually suspected in high-risk individuals (eg, exposure to a high-risk area) with non-specific gastrointestinal symptoms. These symptoms may include nausea, vomiting, abdominal discomfort, or diarrhea lasting > 2 weeks.
If your doctor suspects infection, they will typically request a stool sample for various tests including a fecal occult blood test, stool white blood cells (WBC), and analysis for ova and parasites with stool microscopy. Most intestinal parasites are detected this way. Commonly ordered blood tests include a CMP (comprehensive metabolic panel), lipase, and CBC (complete blood cell count). Individuals with intestinal worms often have an elevated eosinophil count on CBC.
Pinworm infection with Enterobius vermicularis is typically diagnosed with the “scotch tape test” in which tape is placed on the anal mucosa. The eggs of the pinworm typically adhere to the tape, allowing for a visual diagnosis. These worms are not usually detected on stool microscopy for ova and parasites.
Less commonly, intestinal parasites require upper endoscopy or surgical abdominal exploration to confirm the diagnosis and treat infection.
Intestinal worms (helminths) are treated with antiparasitic medications. The entire household often needs to be treated due to high rates of disease transmission. The most commonly prescribed drugs include:
- Albenza (albendazole)
- Vermox (mebendazole)
- Pin-X (pyrantel pamoate)
T. Saginata and D. latum are typically treated with Biltricide (praziquantel). Niclocide (niclosamide) is an alternative option.
Stool should generally be reexamined for eggs once treatment is completed to ensure disease eradication. Approaches to disease prevention in endemic areas include sanitation improvements, education, and widespread antiparasitic therapy. Sanitary practices include treating water and handwashing with soap, particularly after using the restroom.
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- Drugs for Parasitic Infections, 3rd Ed, The Medical Letter, New Rochelle, NY 2013. – https://www.uab.edu/medicine/gorgas/images/docs/syllabus/2015/03_Parasites/RxParasitesMedicalLetter2013.pdf
- World Health Organizaton. Preventive chemotherapy in human helminthiasis: Coordinated use of anthelminthic drugs in control interventions: A manual for health professionals and programme managers. WHO, Geneva 2006 – https://apps.who.int/iris/bitstream/handle/10665/43545/9241547103_eng.pdf;jsessionid=6232FF343704A45592E4A72182BB9EF6?sequence=1