Parasitic Infections


Parasites are organisms that live inside humans or other organisms who act as hosts. They are dependent on their hosts because they are unable to produce food or energy for themselves. Parasites are harmful to humans because they consume needed food, eat away body tissues and cells, and eliminate toxic waste, which makes people sick.

Because of sanitary living conditions in America, parasites do not cause widespread life-threatening infections. In other parts of the world, however, parasitic infections are epidemic. They kill and disable millions of people every year. Parasitic infection cases in the United States are on the rise due to increased travel to and from underdeveloped countries. In addition, parasitic infections can cause severe infections in AIDS patients and other patients with weakened immune systems.

Because parasites can live inside the human body for years without making their presence known, they are more common than one might think. According to a recent study, approximately half of all Americans have at least one form of parasite. Their presence causes a variety of chronic diseases and conditions such as chronic fatigue, weakness, low energy levels, skin rashes, pain, constipation and frequent colds and influenza.


There are two types of parasites: large and small. Large parasites such as intestinal worms are easily seen with the naked eye. These are roundworms, flukes, and tapeworms. They usually lay their eggs on the intestinal walls. As they hatch, the young larvae feed on the food in the intestinal tract. Then they grow, reproduce, and start the cycle all over again. They sometimes dig through the digestive tract to get into the bloodstream, muscles, and other organs where they cause even more havoc. These types of parasites most often cause malnutrition and anemia because they tend to rob the body of essential nutrients it needs.

Small parasites—mostly protozoa and amoebae—are so tiny that they can only be seen with a microscope. These tiny parasites are even more dangerous to the body than the large ones. Although they usually stay in the intestines, they can migrate virtually anywhere in the body: into the bloodstream, muscles, and even vital organs such as the brain, the lungs, or the liver, where they do substantial damage.

Because parasites are everywhere, it is not difficult to become infected. People can become infested through:

  • insect bites
  • walking barefoot
  • eating raw or undercooked pork, beef or fish
  • eating contaminated raw fruits and vegetables
  • eating foods prepared by infected handlers
  • drinking contaminated water
  • contact with infected persons (including sexual contact, kissing, sharing drinks, shaking hands, or sharing toys)
  • inhaling dust that contains parasitic eggs or cysts
  • playing with or picking up pet litter contaminated with parasitic eggs or cysts

In 2002, the Centers for Disease Control (CDC) announced the first documented cases of transplant patients contracting a dangerous parasitic disease from infection with T. cruzi from organs harvested from a Central American donor. The infection caused Chagas disease, causing two of the three donor recipients to die. The CDC was studying additional precautions to screen for parasitic infections like T. cruzi, explaining that even blood donors were not currently screened for the parasite. However, the agency also stressed that tissue graft surgery was still a safe procedure.

Causes & symptoms

Risk factors for getting parasitic infections include:

  • an immune system weakened by disease or long-term exposure to toxic chemicals or environmental pollution
  • prolonged antibiotic use
  • alcohol and/or drug abuse
  • smoking
  • emotional and/or physical stress
  • diet high in fat and sugar and low in fiber
  • food allergies
  • malabsorption syndrome
  • obesity


There are more than 100 types of human parasites. The following describe some of the most common species in America.

ARTHROPODS (INSECTS). In the United States, because of high sanitary standards and a temperate climate, parasitic insects do not flourish. Common bugs such as ticks, mites, fleas, lice, and bedbugs may cause intense itching in affected areas. They are a nuisance but not a major health risk. One exception is the deer tick, which is associated with the debilitating Lyme disease. Other parasites, spread by mosquitoes, cause more serious diseases like western and eastern equine encephalitis, malaria, Dengue fever, and yellow fever.

INTESTINAL PARASITES. Some of the most common intestinal parasites include:

  • Pinworms. This is the most common parasitic infection in the United States. The worm resides in the colon, yet it lays eggs outside the body, usually near the anus, a process that causes severe itching. The disease can be transmitted from one individual to another through dirty hands, clothing, bedclothes, and toys.
  • Tapeworms. The two most common tapeworms are Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm). Taenia solium infestation is caused by eating undercooked pork while Taenia saginata (pork tapeworm) infestation is associated with consuming raw beef. Adult tapeworms may become quite big, some as long as 20 feet (6.1 m). Pork tapeworm is the more harmful. It often causes anemia and weight loss. More seriously, when adult pork tapeworm eggs, excreted in human feces, are ingested by other people (which can happen with poor hygiene and sanitation), the parasitic life cycle that occurs in pigs and cattle takes place in the human host. Once in the human digestive system, the tapeworm eggs, called proglottids, develop into an embryonic form of the parasite called onchospheres that burrow through the intestinal wall and into the bloodstream. From there they migrate into the muscles, eyes, and the brain, a condition called cysticercosis. Cysts in the brain often cause epileptic seizures.
  • Protozoa (one-celled organisms) such as Giardia lamblia, Entamoeba histolytica, or Cryptosporidium. These organisms are some of the most common and infectious parasites in the world. They can be transmitted through contaminated food and water. They can also be spread from one person to another. Protozoa may spread throughout the body, causing abscesses in the lungs, liver, heart, and brain. Cramps, watery diarrhea, abdominal pain, and serious weight loss are common symptoms of Giardia infection. Entamoeba histolytica can cause dysentery, a severe form of intestinal infection, as well as liver and lung damage. Cryptosporidia can cause severe diarrhea in AIDS or cancer patients who have weakened immune systems.

CNS PARASITIC INFECTIONS. Toxoplasma gondii is the most common parasite that invades the central nervous system (CNS). Humans become infected with this organism by eating raw or undercooked meat or by handling infected cat litter, which can contain eggs. Pregnant women who are infected may miscarry or deliver stillborn babies. Infected babies are born with congenital toxoplasmosis, and have symptoms that include eye inflammation, blindness, jaundice, seizures, abnormally small or large heads, and mental retardation. In people with weakened immune systems, such as AIDS patients, toxoplasmosis can affect the whole body, causing inflammation, convulsions, trembling, headache, confusion, paralysis in half of the body, or coma.


Parasitic infections are difficult to diagnose because many patients exhibit only vague symptoms or no symptoms at all. The following symptoms, however, may indicate parasitic infections:

  • Diarrhea with foul-smelling stool that becomes worse in the later part of the day.
  • Sudden changes in bowel habits (e.g. constipation that changes to soft and watery stool).
  • Constant rumbling and gurgling in the stomach area unrelated to hunger or eating.
  • Heartburn or chest pain.
  • Flulike symptoms such as coughing, fever, and nasal congestion.
  • Nonspecific food allergies.
  • Itching around the nose, ears, and anus, especially at night.
  • Losing weight with constant hunger.

Other symptoms of parasitic infections include anemia, blood in the stool, bloating, diarrhea, gas, loss of appetite, intestinal obstruction, nausea, vomiting, sore mouth and gums, excessive nose picking, grinding teeth at night, chronic fatigue, headaches, muscle aches and pains, shortness of breath, skin rashes, depression, and memory loss.


The following tests may be used to help doctors diagnose parasitic infections:

  • Ova and parasite (O & P) test. Three to six stool samples are collected every one or two days to look for eggs and parasites.
  • Cellophane tape (applied to the anal area). Ova (eggs) that stick to the tape prove pinworm infestation.
  • Endoscopy. This procedure is used to obtain samples from the duodenum (the upper part of the small intestine), which are then analyzed for the presence of parasites.
  • Urine sample and vaginal swab to detect Trichomonas, a parasite that causes vaginitis.
  • Blood tests. High levels of eosinophils (a type of white blood cell) indicate infections. Antibodies against the parasites may also be detected.
  • X-ray, MRI, and CT scans. X-rays detect lesions in internal organs. Computed axial tomography (CT) scans and magnetic resonance imaging (MRI) are used to diagnose CNS parasitic infections.

Infected patients who are treated with antiparasitic drugs or herbal remedies should be retested twice at the end of the treatment program; the two tests should be given one month apart.


Alternative therapies for parasitic infections reduce parasitic infections by improving nutrition and strengthening the immune system through herbal therapy and Ayurvedic medicine. Some herbal remedies are directly antiparasitic, and actually eliminate the organisms that cause disease. Patients taking allopathic antiparasitic remedies should consult their doctor before using any of these herbs. Care should be taken before giving them to children as they easily overdose.

Nutritional therapy

The following dietary changes may help prevent or treat parasitic infections:

  • Eating a well-balanced diet with lots of fiber, vegetables, fruits, whole grains, nuts, and seeds. Fiber helps eliminate worms from the intestines; good nutrition improves immune function and protects the body against parasitic invasion.
  • Limiting dairy foods, sugar, and fat. Parasites thrive on these foods.
  • Avoiding raw or undercooked fish, pork, or beef.
  • Take daily multivitamin/mineral supplements to prevent malnutrition and improve immune function.
  • Supplementing the diet with probiotics such as Lactobacillus acidophilus, Bifidobacteria, and other beneficial intestinal bacteria that cultivate normal intestinal flora and suppress the spreading of parasites.

Herbal therapy

Herbal treatment should be given in combination with supportive dietary treatment and continued until the worms are completely eradicated. The following herbs are helpful in treating parasitic infestations:

  • Melaleuca alternifolia (tea tree) oil. First discovered by Australian aborigines, tea tree oil has many uses, including treating intestinal parasites, lice, and ticks.
  • Artemisia annua (wormwood herb) and citrus seed extract. These can be used together to help eliminate intestinal parasites such as Giardia lamblia.
  • Berberine-containing herbs. Berberine is an antimicrobial alkaloid that can prevent parasites from attaching to the intestinal walls of human hosts. One study found that berberine was as effective against amoebal Giardia lamblia as metronidazole, the standard treatment. Herbs that contain berberine include goldenseal (Hydrastis canadensis), barberry (Berberis vulgaris), Oregon grape (Berberis aquifolium), and goldthread (Coptis chinensis).

Ayurvedic medicine

Momordica charantia (bitter melon) is a very safe remedy for pinworm infection. The melon is a vegetable shaped like a cucumber with a bitter taste. It can be found in most Oriental markets. It should be sliced thinly and eaten raw with other vegetables to reduce its bitter taste. Daily consumption of one to two bitter melons per day for seven to 10 days can eliminate pinworm infection. Patients may want to repeat the regimen after several months to prevent reinfection. Chinese herbal combinations also help treat parasitic infections by supporting the gastrointestinal system, stimulating immune response, and killing parasites.

Insect infestations

Infestations with lice, ticks, fleas, or bedbugs can be controlled by insecticides and attention to hygiene and household or environmental conatct.

Intestinal parasites

Treatment for intestinal parasites usually involves antiparasitic drugs. Depending on the severity of the condition and the species involved, drug treatment may include one (or more) of the following drugs: albendazole, furazolidone, iodoquinol, mebendazole, metronidazole, niclosamide, paromomycin, pyrantel pamoate, pyrimethamine, quinacrine, sulfadiazine or thiabendazole. To prevent reinfection and transmission of disease, thorough cleaning of hands, clothes, sheets, and toys is recommended. Treatments should involve all members of the family and repeated treatments may be necessary.

CNS parasitic infections

Babies or AIDS patients with toxoplasmosis are often given spiramycin or sulfadiazine plus pyrimethamine. Treatment may be continued indefinitely for AIDS patients to prevent recurrence.

Expected results

Though parasitic infections are difficult to diagnose, complete recovery from infestation can be effected with appropriate herbal therapy or antiparasitic drugs. Because reinfestation is common, multiple treatments may be necessary.


The following measures can help prevent parasitic infections:

  • Washing hands before eating and after using the restroom.
  • Wearing gloves when gardening or working with soil or sand because soil can be contaminated with eggs or cysts of parasites.
  • Pregnant women should avoid handling cat litter.
  • Not allowing children to be licked or kissed by pets that are not dewormed regularly.
  • Washing fresh vegetables carefully. Many people get Entamoeba histolytica by eating contaminated raw fruit and vegetables.
  • Avoiding eating raw meat, which may contain Giardia lamblia.
  • Wearing long-sleeved shirts, long pants, and boots when walking in the woods. In addition, spraying insect repellent on clothing to prevent tick bites.


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Mai Tran

Teresa G. Odle