Comparison of conventional and immunofluorescent techniques for the detection of Entamoeba histolytica in rectal biopsies.

Two comparative studies of six staining techniques in detection of Entamoeba histolytica in rectal biopsies were performed. The techniques evaluated were direct and indirect fluorescent antibody technique, and four conventional stains: PAS, H & E, Trichrome, and PTAH). On ethanol-fixed tissue, the direct fluorescent antibody technique was the most sensitive, detecting amoebas in 84% of rectal biopsies from 19 aspirate-positive dysentery patients. PAS staining was specific, almost as sensitive, and amoebas could be rapidly detected. The other three conventional methods, however, detected amoebas in only 53--58% of the aspirate-positive patients and required considerable efforts to find the amoebas. The indirect fluorescent antibody technique performed on ethanol-fixed tissues was comparable to the direct technique. The same technique used on formalin-fixed tissues had high background staining, but amoebas could still be detected more efficiently than with conventional staining. Following 20 hr or more treatment with metronidazole, no patient had amoebas detectable in their rectal biopsies by any technique used. Patients with amoebic dysentery and necrotic ulcers on protoscopy had amoebas detected more frequently in rectal biopsy than did patients with mild disease as determined by proctoscopy. Entamoeba histolytica in rectal biopsies can be detected most easily in ethanol-fixed tissue stained with either a fluorescent antibody or with PAS. If amoebas are not detected in the rectal biopsy, amoebic colitis cannot be excluded.