In a small pilot study the parasite cure rate (PCR) of non-invasive amoebiasis was compared after treatment with metronidazole 800 mg three times daily or tinidazole 600 mg twice daily for five days. Both treatment regimens were found to be highly unfavourable with PCRs of 44 and nil respectively, in contrast to previous published results showing PCR over 80%. Treatment of non-invasive amoebiasis--a comparison between tinidazole and metronidazole. Pehrson P, Bengtsson E. Ann Trop Med Parasitol 1984 Oct;78(5):505-8

One hundred and fifteen persons with asymptomatic Entamoeba histolytica or E. hartmanni infection, or both, were given metronidazole (750 mg three times daily for 5 days), tinidazole (1 g twice daily on 2 consecutive days), or a starch placebo. Three post-treatment stools were examined in the 2 weeks following initiation of treatment. Cysts of E. histolytica reappeared in the stools of 37% of 30 given metronidazole, 62% of 34 given tinidazole, and 70% of 31 given placebo. Cysts of E. hartmanni reappeared in the stools of 46% of 24 given metronidazole, 69% of 16 given tinidazole, and 90% of 10 given placebo. Rapid absorption and short duration of treatment make both drugs ineffective for the treatment of ameba carriers. Double-blind test of metronidazole and tinidazole in the treatment of asymptomatic Entamoeba histolytica and Entamoeba hartmanni carriers. Spillmann R, AyalaSC, Sanchez CE. Am J Trop Med Hyg. 1976 Jul;25(4):549-51.

Unique in that it is effective both in the bowel lumen and in tissues, metronidazole has been reported to eradicate only up to 50% of luminal** infections. This statement has support from a study of 36 patients with amoebic liver abscess for whom the hepatic lesions were cleared; but 20 were recolonized in the intestine, 16 asymptomatically. This was ascribed to the pharmacokinetics of metronidazole cycling in the liver and the action of metronidazole against trophozoites but not invariable eradication of cysts, creating E. histolytica carrier states.

Current recommendations suggest the use of metronidazole or tinidazole PLUS the luminal amoebicide diloxanide furoate or iodoquinol, with other combinations (including paromomycin, tetracycline, and chloroquine) depending on the severity of the infection and site, i.e., whether it is intraluminal, invasive, or abscessed .
Drug Targets and Mechanisms of Resistance in the Anaerobic Protozoa
Peter Upcroft* and Jacqueline A. Upcroft
Queensland Institute of Medical Research and The Tropical Health Program, Australia

Nitazoxanide was more toxic than metronidazole and albendazole against E. histolytica
In vitro effect of nitazoxanide against Entamoeba histolytica , Giardia intestinalis and Trichomonas vaginalis trophozoites. J Eukaryot Microbiol 2002 May-Jun;49(3):201-8
Cedillo-Rivera R, Chavez B, Gonzalez-Robles A, Tapia A, Yepez-Mulia L.

Thirty-eight (81%) of 47 patients in the nitazoxanide treatment group resolved diarrhea within 7 days (median, 3 days) after initiation of treatment, versus 17 (40%) of 42 in the placebo group (P=.0002).
Treatment of diarrhea caused by Giardia intestinalis and Entamoeba histolytica or E. dispar: a randomized, double-blind, placebo-controlled study of nitazoxanide.
Rossignol JF, Ayoub A, Ayers MS.. J Infect Dis 2001 Aug 1;184(3):381-4,

A study from Africa compared four amoebicide drugs treatments on 300 symptomatic patients over a 5 month period. Seventy-six percent submitted 3 follow up stool samples.
The results were: Metronidazole + Oxytetracycline (tetracycline) - 10.9% continued to excrete E.histo. cysts. Di-iodohydroxyquinoline (an older, more toxic version of Iodoquinol/Yodoxin) and Oxytetracycline : 25.5% continued to excrete E.histo. cysts.
This figure fell to 20% when *Dehydroemetine was added. Clioquinol and Oxytetracycline - 27.5% continued to excrete the parasite.

*Dehydroemetin can cause serious side effects and is usually reserved for dangerously ill patients


I can corroborate about the lack of knowledge doctors often have about parasites, symptoms, testing and treatment. I have heard many times that Eh is not pathological. I saw about 10 different doctors. It is remarkable the ignorance of this very serious infection." Gary. 2004. More below.

Entamoeba histolytica

E.histolytica is an invasive parasite capable of causing life-threatening intestinal and extra-intestinal disease. E.histolytica can invade the liver, lung and other bodily sites by penetrating the intestinal mucosal barrier.

It has a worldwide distribution and is the third leading cause of death by parasitic infection. It was first documented in 1875 and is estimated to cause between 50,000 and 100,000 deaths every year. Ninety percent of those infected have no symptoms.


Symptoms range from mild diarrhoea to hemorrhagic dysentery.

Cases of mild diarrhoea caused by E.histo. are often misdiagnosed as Irritable Bowel Syndrome (personal data).

Many infected individuals are asymptomatic but can infect others via intermittent shedding of cysts in the stool.

Symptoms may include:

Rare complications:

Amoebic colitis including necrotising (fulminant) colitis (approx. 0.5% of patients) which has a mortality rate of 40%. Nectrotising colitis can occur in the malnourished, during corticosteroid use (steroids used to suppress inflammatory response), in young children & during pregnancy.

Individuals with liver abscess may not excrete the organism in the stool. In these cases stool antigen tests may not be suitable for the diagnoses of amoebic liver abscess.

Although blood tests for antibodies against E histolytica are approx. 80% accurate, the detection rate drops dramatically after treatment with metrondazole. In one study of 75 patients all positive for amoebic liver abscess, only 15% tested positive after treatment with metronidazole (Flagyl). ( J Clin Microbiol. 2000;38:3235-3239) .

Vaginal infection:


Genital amebiasis is a rare complication of infection with Entamoeba histolytica, even in areas where the pathogen is endemic. We describe a patient who apparently contracted intestinal amebiasis on a trip to Mexico and who presented with ulcerative vulvovaginitis 2 months later. Her condition rapidly progressed to severe necrotizing vulvovaginitis that required a radical vulvectomy. Histopathologic examination of the surgical specimen revealed the presence of E. histolytica trophozoites. The patient recovered after surgery and antiamebic therapy. Infect Dis 1995 Mar;20(3):700-2 Cl


Severe vaginal infection with Entamoeba histolytica in a woman who recently returned from Mexico: case report and review. Citronberg RJ, Semel JD. Section of Infectious Disease, Rush Medical College, Chicago, Illinois, USA.


Exposure to E.histolytica cysts is similar to that of D.fragilis and B.hominis:


By stool testing:

Examination of a single stool specimen is approx. 33% accurate.

Because the cysts of E.histolytica shed intermittently in the stool and may not be present at the time of testing at least three to six stool examinations are recommended.

The following may interfere with recovery of the parasite and should be avoided for three weeks prior to submitting samples for testing. Discuss with your doctor before stopping any medications.

Tetracyclines, sulfonamides, antiprotozoal agents, laxatives, antacids, castor oil, magnesium hydroxide, barium sulphate, bismuth kaolin compounds and hypertonic salts, anti-parasitic herbs, certain laxatives & mineral compounds, antibiotics, antacids, antidiarrheals.

STOOL TESTING BY ELISA (Enzyme-Linked Immunosorbent Assay):

Parasites are composed of cell surface molecules called lectins, which enable the parasite to adhere to the bowel. ELISA detects the lectins specific to E.histolytica and is performed on fresh, unfixed samples. Most labs around the world perform antigen testing on request.


The Centre for Digestive Diseases in Sydney, Australia prescribe a combination of

Secnidazole 400 mg (30 Capsules) 3 times a day
Diloxanide Furoate 500mg (30 Capsules) 3 times a day

Download the CDD's treatment sheet here.

Other treatments:

METRONIDAZOLE/TINIDAZOLE - See sidebar and case histories below.

NITAZOXINIDE - See side bar as well as case histories below.

The experiences of people infected with this bug:

Garey endured symptoms typical of a bowel infection for four years before E. histolytica was diagnosed.

Garey's attempts to find a doctor who believed that E.histolytica was causing his symptoms proved challenging. The result came from a lab much maligned at the time by orhodox medical practitioners. The lab Great Smokies (now Genova), stood accused of reporting unimportant parasites - specifically D.fragilis and Blasto. Any patient in receipt of a positive result from a non-standard source could expect short shrift from their doctor - if you got to see them at all that is. Garey couldn't even get an appointment:

"We have a fairly sophisticated infectious disease clinic at the medical school complex here in Portland. At one point I tried to make an appointment about my infection via a naturopathic doctor based on a positive lab test through Great Smokies Diag. I was refused to be seen. The reason given was that I was not thought to be sick enough to require the services of a specialist".

After four years of searching Garey found a specialist endocrinologist interested in treating parasites. To Garey's relief he was a dr "who thinks outside the square".

Under the guidance of this doctor Garey made a complete recovery after being prescribed a combination of Humatin and Nitazoxinide.

Garey wrote to his first primary care physician outlining the extent of his search for a treatment, enduring misdiagnoses and inadequate treatment for four years until he finally found a dr who did not dismiss the positive result. The doctor replied, by registered mail, to inform Garey that "he would no longer be willing to see me for any reason".

"I can corroborate about the lack of knowledge doctors often have about parasites, symptoms, testing and treatment. I have heard many times that Eh is not pathological. I saw about 10 different doctors. It is remarkable the ignorance of this very serious infection."

Here is what cured Garey:

Nitazoxanide 600mg 4 x daily for four days
Paromomycin (Humatin) 250mg 3 x daily for five days.*

March 2004

*If this treatment helps you please please drop me a line. Your experience will help others make an informed decision about their own treatment.


P. was diagnosed with both E.histolytica and B. hominis. Two lots of Flagyl failed to help. Post treatment stool testing was negative for both E.histolytica and Blasto.

The result of other tests, including a colonoscopy and barium meal x-ray, were all normal.

P. questioned whether the parasites could still be around, despite not showing up in stool samples. He was assured that "the amoebic dysentry could not be still be around in my gut".


In 2001 S. became unwell after a food poisoning incident. Luckily for her a rheumotologist recognised her symptoms as similar to his wife's who had been recently diagnosed with E.h.:

"My symptoms were severe, excrutiating pain at times, in my back. A constant lower back pain, which eventually became debilitating. I could barely walk, and could not lift my son. I also had extremely heavy period, later becoming irregular. Fatique, sleeplessness, frequent urination, skin rashes, as well as extreme itching of my skin. Alternating bouts of diarrhea and constipation. Constant feeling of bloating and gas. My husband, after the inital "food poisoining" incident, had the extreme back pain and was misdiagnosed with sciatica. He was given pain medication for approximately three months.

Every doctor we saw always quickly dismissed our suspicions of acquiring a parasite from shrimp we had from Ecuador, as impossible. Finally, one doctor decided to test for it by ELISA but the test was negative.

Finally, a rheumatologist I went too, talked to me for 45 minutes and recognized my symptoms as being the same as his wifes. She recently had been diagnosed with an amoeba.(Little did he know we were infected with the exact same bug.) He sent me to a parasitologist on fith avenue in NYC., NY. Within two days, after biopsy, he had a diagnosis! The medicine, humatin and doxycyline, had to be shipped from the city, but three months later we are negative and on the road to recovery! (US. 3 Sept 02)


D. had been ill for 6 years. His health problem started after a holiday in Mexico. His symptoms included chronic fatigue and digestive symptoms severe enough to interfere with his ability to work. He was never tested for parasites, despite being a visitor to a country where parasites are endemic, and ending up with symptoms typical of a parasitic infection.

Great Smokies Diagnostics (now Genova) diagnosed E.histolytica:

"Good news - in a way, anyway. I just found out that my stool tested positive for entamoeba histolytica! Probably from the trip to Mexico almost 6 years ago." Feb 02


"My symptoms are upper bloating, reflux, heartburn, bad taste in mouth, and sinus trouble. I have been to many docs and have tried many meds. I even had surgery for the reflux which did not work. I have been dealing with this for 4 years. I probably burp 100 times a day. Well last week I decided to see a tropical disease expert in NYC. He did a sigmoinoscopy ( I think that is what it is called). He called me today to tell me that he found mucous, inflamation, and charcoal crystals**??? He says that these are signs of parasitic infection and he is 99% sure I have an ameba called Histelica? He wants to treat me with a 2 week dose of flagyl. I think I may go back for another sig, to see if he can find the bug for sure. Any opinions or advice is greatly appreciated.
P. 13 March 02

Further investigation by sigmoidoscopy confirmed infection with E.histolytica.

**Charcot-Leyden crystals are formed from the breakdown of immune eosinophils and may be seen in the stool or sputum of patients with parasitic diseases. 


Entamoeba histolytica Schaudinn, 1903 and Entamoeba dispar Brumpt, 1925: differences in their cell surfaces and in the bacteria-containing vacuoles. J Eukaryot Microbiol 2002 May-Jun;49(3):209-19. Pimenta PF, Diamond LS, Mirelman D.

Amebiasis, Robert Swords, MD. eMedicine Journal, February 22 2002, Volume 3, Number 2 on-line

Molecular cloning of a 30-kilodalton lysine-rich surface antigen from a nonpathogenic Entamoeba histolytica strain and its expression in a pathogenic strain. Infect. Immun. 63: 917-925. Bracha, R., Nuchamowitz, Y. and Mirelman, D. (1995)