The most common intestinal parasite is a threadworm. These worms live in the intestine and rectum and can cause itching around the anus, especially at night.
Doctors diagnose threadworm infection by finding worm segments or worm eggs in a stool sample. They may also ask you to do a tape test. Place a piece of clear tape over the skin around your anus, and then pull it off. Any pinworm eggs stuck to the tape will be identified under a microscope.
Tapeworms, or flukes, are parasites that attach to the intestines. They grow slowly and usually cause no symptoms. But they can be dangerous, especially in children who eat undercooked meat or fish from developing parts of the world. A tapeworm has suckers and hook-like portions that can get stuck in the intestines. They leave the body in a fecal matter called a segment, which can be passed with bowel movements. The segments contain eggs, which can be seen in a stool sample that’s been viewed under a microscope.
If newly hatched tapeworm larvae escape the digestive tract, they can grow in the liver and develop cysts. Those cysts reduce the blood supply to the healthy parts of the liver, which can cause jaundice (yellowing of the skin and eyes) or pancreatitis. The cysts can also move to the brain, where they can cause seizures and other problems. Doctors treat tapeworm infections with prescription medicines. They may also order a CT scan or MRI to find the cysts in the liver, lungs, and other organs.
Pinworms are tiny, thread-like worms that live in the colon and rectum. They cause intense itching, especially at night. Sometimes the worms migrate into the vagina or urinary tract, and this itching is more severe. Itching in this area is called peri-anal itching or pruritis vaginalis.
The worms lay eggs on the skin around the anus. The eggs look like little pieces of cotton thread, so a doctor can sometimes see them with a flashlight and a mirror when checking the perianal area. The best time to check for pinworms is first thing in the morning — before a person bathes or uses the toilet. The doctor can also use the tape test, which involves placing a piece of clear tape sticky side up against the skin near the anus and looking for eggs under a microscope.
A pinworm infection is treated with medicine that kills the worms. A doctor may prescribe the drug pyrantel pamoate (Reese’s Pinworm Medication, Pin-X) for the infected individual and any family members who have symptoms. A second dose of the medication is often needed 2 weeks later to kill any worms that have hatched.
Giardia is a tiny parasite that can cause diarrhea. It spreads when you touch germy things with dirty hands, like a toilet flush handle or salt shaker, and then put them in your mouth. Giardia can also be spread by drinking water that has been contaminated with feces (poop) from people or animals. This can happen if you travel to places where the locals don’t boil their drinking water or if you swallow water while swimming in lakes, rivers, springs or streams. Giardia can also be spread when a person has unprotected anal sex.
Diarrhea, bloating, gas and fatigue are common symptoms of this parasite. If you have severe, bloody or greasy diarrhea, see your doctor. Some giardia infections may be difficult to detect with a stool test. Often, the best way to check for these infections is with a direct smear of your stool or a special zinc sulfate flotation test. You might have giardia cysts that are not visible on a fecal smear, however, and these will need a different test to detect.
Ascariasis, caused by the roundworm Ascaris lumbricoides, is common in areas with poor sanitation. People can become infected by swallowing Ascaris eggs found in soil, food or water that has been contaminated with human feces. The eggs remain infectious in the soil for years. People can also ingest the eggs when they don’t wash their hands thoroughly before eating contaminated food or vegetables.
The infection can be asymptomatic or cause abdominal pain, diarrhea and nausea. Heavy infestations can lead to intestinal blockage and impair growth in children.
Your family doctor may examine you for symptoms and order a stool exam. If you have a bowel obstruction, your doctor may refer you to a gastroenterologist. If you have a severe infestation, surgery may be needed to remove the worms and repair any damage they’ve caused. Your doctor can also order a blood test to check for any damage to your liver or bile ducts. If these are impacted, you might need a cholecystectomy or biliary removal procedure.