Blastocystis Species: Guilty or Innocent?

Abstract

Blastocystis spp. was previously considered to be a member of normal intestinal flora; it is now receiving increased attention as a potential causative agent of human intestinal disease. The present study attempts to investigate the pathogenicity of Blastocystis spp. in clinically symptomatic patients. Eighty-six immunocompetent patients with intestinal Blastocystis spp. were evaluated clinically. Two consecutive stool samples were examined by wet mount, modified formol ethyl acetate concentration method and trichrome and Kinyoun acid-fast staining. Presence of more than 10 various morphological forms of Blastocystis spp. under 40× magnification was taken as a criterion for the presence of protozoan. Patients with other pathogens were excluded from the study. Metronidazole was administered for five to seven days. After treatment, stool sample of patients were re-examined for Blastocystis spp. There were 39 males and 47 females with a mean age of 39.8 years ± 18.8 (range 19–62 years). Abdominal pain was the most frequent symptom (77.9%) followed by diarrhea (65.1%). A second stool specimen was obtained from 61 (70.9%) patients after metronidazole therapy. Consecutive investigation revealed no intestinal protozoa in 56 (91.8%) patients. Symptoms persisted in five patients. Out of 56 patients who complained of diarrhea, 51 showed improvement in symptomology with no protozoan found. If all other pathogens and factors causing intestinal pathologies are ruled out and only Blastocystis spp. is present in symptomatic patients, it is logical to consider them as pathogenic rather than commensals and treatment can be initiated in such cases. However, further studies for genetic association and prevalence are needed to strengthen this view.