D. fragilis and B. hominis: neglected human protozoa.
J. J. Windsor.
The Biomedical Scientist. July 2007. Pages 524-27.

"Many of the clinical symptoms associated with IBS are non-specific and have also been reported in patients infected with D. fragilis and B. hominis. Irritable bowel syndrome is usually diagnosed clinically according to the Rome II criteria. Many laboratories in the UK would not be able to exclude D. fragilis and B. hominis, therefore it is possible that some patients infected with these parasites could be misdiagnosed as having IBS. Anecdotal evidence suggests that many patients infected with these parasites are indeed being misdiagnosed as having IBS"

Blastocystis hominis and bowel diseases.
Turkiye Parazitol Derg., 2006;30(1):72-76

"The clinical consequences of B. hominis infection are mainly diarrhea and abdominal pain as well as nonspecific gastrointestinal symptoms such as nausea, anorexia, vomiting, weight loss, lassitude, dizziness, and flatulence. Case reports and series have suggested a pathogenic role of B. hominis in causing intestinal inflammation. Also some studies have suggested that inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are associated with B. hominis infection. The investigators indicate that the stools of all patients presenting with IBD or IBS should be examined, and culture methods for B. hominis carried out. Invasion and mucosal inflammation of the intestine with B. hominis have been observed in studies of gnotobiotic guinea pigs."

Blastocystis hominis infection in irritable bowel syndrome patients.
Tungtrongchitr A
Southeast Asian J Trop Med Public Health.
2004 Sep;35(3):705-10.

IBS and control cases positive for B.hominis were treated with 1,200mg of metronidazole daily for 7 days and the stool was reinvestigated for B.hominis. The results show that B.hominis infection in IBS patients could not be fully cured using standard treatment (1,200mg of metronidazole daily for 7 days).

Br J Biomed Sci. 2004;61(2):75-7.

"B. hominis resistance to furazolidone, metronidazole and ciprofloxacin at 0.01 mg/mL was 32% (8/25), 40% (10/25) and 100% (25/25), respectively. B. hominis isolates varied in their degree of susceptibility to the three drugs studied, being greater with furazolidone than with metronidazole, and complete resistance with ciprofloxacin."

April 2002 - Biomedical Scientist.

In patients diagnosed with chronic irritable bowel syndrome (IBS), faecal samples are placed directly into fixative and then stained with an iron haematoxylin. Using this technique, 40% of IBS patients were shown to be infected with B. hominis.

Blastocystis hominis modulates immune responses
and cytokine release in colonic epithelial cells
by H.Y. Long et al
(Parasitology Res (2001) 87: 1029-1030)

It might be speculated that B.hominis downregulates the host immune responses in the early phase of the infection, in order to improve its survival. This seems to be a common evasion mechanism of parasites, as it has also been demonstrated for Toxoplasma gondii (Denney et al. 1999). Further it may also be expected that this effect of B.hominis could indirectly facilitate the progress of infection by other opportunistic pathogens. The results presented here indicate that B.hominis is able to induce and modulate the production of inflammatory cytokines in intestinal epithelial cells.

Establishing Cultures of Entamoeba in vitro
London School of Hygiene & Tropical Medicine, 2000

Blastocystis hominis may be the most common parasitic infection of humans. This organism is often missed on stool examination but grows luxuriantly in all the media used to cultivate xenic Entamoeba.

Isolate resistance of Blastocystis hominis to metronidazole.
Haresh K, Suresh K, Khairul Anus A, Saminathan S.
Trop Med Int Health. 1999 Apr;4(4):274-7.

The study shows that isolates of B. hominis of different geographical origin have different levels of resistance to metronidazole. The search for more effective drugs to eliminate th parasite appears inevitable, especially since surviving parasites from metronidazole cultures show greater ability to multiply in subcultures than controls.
[Ineffectual treatment with drugs increases the strength of the culture in the patient.]

Urticaria by Blastocystis hominis.
Armentia A, et al.
Allergol Immunopathol (Madr) 1993 Jul-Aug;21(4):149-51

Urticaria and angioedema are easily recognized disorders, but in at least 70 percent of individuals, chronic episodes of urticaria are of unknown causes. We present 10 cases of chronic urticaria associated parasitation by Blastocystis hominis. This parasite has not been previously related with urticaria.
[Urticaria (hives) consists of localised swelling on the skin often accompanied by an itchy rash. The symptoms usually last for a few hours before eventually fading away.]

Blastocystis hominis - Past and Future
C.H. Zierdt
Clinical Micro. Reviews. Jan 1991 Vol 4, No 1; 61-79