Dr. Weyrich's Naturopathic Functional Medicine Notebook is a collection of information on topics of interest to Dr. Weyrich that may be of interest to the world wide audience. Due to limitations of time, not all information that Dr. Weyrich knows or would like to further research is published here. Dr. Weyrich welcomes financial contributions to support specific research topics, as well as copies of non-free access journal articles for him to review on a topic. Constructive criticism is also welcome.


Overview of Parasites

Parasites are any of a number of worms or microscopic organisms that can infect humans. Many are transmitted by ingestion of contaminated food or water, although other modes of transmission are also possible.

Parasites are made up of eukaryotic cells similar to their human hosts, in contrast to bacteria that have distinctly different cells. This makes treatment of parasitic infections harder than the treatment of bacterial infections, since it is harder to find chemical agents that are toxic to the infective agent without also being toxic to the human host.

Many species of parasites are uncommon in North American populations but common in third world countries where sanitary conditions are poorer. However, with increased international travel, many parasites previously associated only with third world countries are showing up in North America, requiring a higher level of suspicion of parasites than in years past.


Signs and Symptoms of Parasites

  • Gastrointestinal pain
  • Diarrhea
  • Nausea / reduced food intake
  • Pruritus ani (especially pinworm)
  • Intestinal obstruction (especially roundworm)
  • Appendicitis (especially roundworm)
  • Intestinal bleeding and anemia
  • Malabsorption of nutrients and micronutrients
  • Retardation of growth and cognitive development
  • Surgical complications such as obstruction, rectal prolapse and abscess

Diagnosis of Parasites

Isolation of parasites or their eggs (ova) from the patient's feces is the gold standard in diagnosing parasites. However, due to the complex life-cycles of many parasites, it is easy to fail to find parasites or ova in a single sample. For this reason, at least three samples are generally collected.

Colonoscopy and biopsy.


Differential Diagnosis of Parasites

  • Pinworm (Enterobius vermicularis, Oxyuris vermicularis): perianal itching, intestinal abscesses and bleeding. Nematode infestation of the large intestine. Eggs may be found in the perianal area; they can be transferred with a cellophane tape swab to a slide for microscopic inspection. Worms may also be seen in stools, and sometimes around the anus.
  • Roundworm (Ascaris lumbricoides): Nematode infestation of the jejunum. May cause intestinal, biliary, or pancreatic obstruction; appendicitis. Eggs may be diagnosed by a simple smear of stools.
  • Hookworm (Necator americanus, Ancylostomia duodenale, Strongyloidea): Symptoms include iron-deficient anemia, physical and mental retardation, cardiac complications. DX: stool analysis.
  • Balantidium coli: A ciliated protozoa that commonly infests the intestines of swine. May cause diarrhea, dysentery, vomiting, weakness, and occasional ulceration of the large intestine. DX: stool analysis.
  • Entamoebia histolytica: E. histolytica and other amoebas cause irregular ulcers in the rectum with red borders and gray bases. May also invade the liver. DX: stool analysis, biopsy of ulcer, detection of antibodies in the blood. CT scan or ultrasound may reveal abscess due to liver involvement.
  • Giardia lamblia: A flagellated protozoa that infests the small intestine. May cause diarrhea or dysentery. DX: stool analysis, stool antigen.
  • Strongyloides stercoralis: Roundworm that infests intestines and lungs. Most common in southern rural USA. Symptoms may include rash, pneumonia, diarrhea. May be life-threatening. DX: stool analysis.
  • Tapeworm (Taenia spp., Diphyllobothrium latum, Hymenolepis spp., Echinococcus granulosus): May be asymptomatic, but in some cases can cause intestinal obstruction, life-threatening liver and pericardium infestations, or seizures [Tabers2013]. DX: Eggs can be swabbed from perianal areas and examined, stool analysis.
  • Trichinella spiralis: Nematode worm found in undercooked meat, especially pork. Infestation may result in death within six weeks. DX: muscle biopsy to determine the presence of encysted larvae (stool analysis not useful).
  • Whipworm (Trichuris trichiura): Nematode infestation of the large intestine. Symptoms include blood-streaked stools, rectal prolapse, iron-deficiency anemia, malnutrition. DX: stool analysis.
  • Liver Fluke (Fasciola hepatica): Trematode worm commonly infesting herbivores (cattle, sheep, etc.). Causes enlarged and painful liver, fever. DX: stool analysis.
  • Lung Fluke (Paragonimus spp.): Trematode worm commonly infesting dogs, cats, swine, crabs, and crayfish. Presentation may resemble TB.

Treatment of Parasites

Re-infection is common in many parasitic infestations; therefore, all members of the household should be treated, and good hygiene is a must.
  • Pinworm (Enterobius vermicularis, Oxyuris vermicularis): Pyrantel pamoate, albendazole, mebendazole. Clean bed linens and house daily during treatment [Tabers2013].
  • Roundworm (Ascaris lumbricoides): Pyrantel pamoate is the drug of choice, mebendazole is also effective [Tabers2013].
  • Hookworm (Necator americanus, Ancylostomia duodenale, Strongyloidea): Mebendazole, pyrantel pamoate. Iron supplementation for anemia [Tabers2013].
  • Balantidium coli: Tetracyclines, metronidazole, paromomycin [Tabers2013].
  • Entamoebia histolytica: Asymptomatic patients: paromomycin (500 mg PO TID * 7 days) or iodoquinol (650 mg PO TID for 20 days). Dysentery and liver abscesses are treated with metronidazole (750 mg PO TID * 10 days) followed by iodoquinol (650 mg PO TID for 20 days) [Tabers2013].
  • Giardia lamblia: Metronidazole, albendazole [Tabers2013].
  • Strongyloides stercoralis: Thiabendazole or mebendazole. Repeated courses of treatment may be necessary [Tabers2013].
  • Tapeworm (Taenia spp., Diphyllobothrium latum, Hymenolepis spp., Echinococcus granulosus:
  • Trichinella spiralis):
  • Whipworm (Trichuris trichiura): Mebendazole is drug of choice, albendazole, ivermectin also useful [Tabers2013].
  • Liver Fluke (Fasciola hepatica):
  • Lung Fluke (Paragonimus spp.):

Prevention of Parasites

Improved sanitation, hygiene, boiling water, adequately cooking foods.

References for Parasites