VALUE OF MICROSCOPY IN THE DIAGNOSIS OF DYSENTERY ASSOCIATED WITH INVASIVE ENTAMOEBA-HISTOLYTICA

Aims-To assess the reliability of the detection of erythrophagocytic a moebic trophozoites in stool samples in the diagnosis of dysentery ass ociated with invasive Entamoeba histolytica. Methods-Amoebic culture w as carried out on single stool samples collected from patients from Me xico, Colombia, and Bangladesh. The stools had been examined by light microscopy. Amoebic dysentery was diagnosed when erythrophagocytic E h istolytica trophozoites were observed in a case of bloody diarrhoea. E histolytica isolates were characterised by isoenzyme electrophoresis and results correlated with microscopical findings in stools. Statisti cal analysis was performed using the chi(2) test. Results-Where erythr ophagocytic amoebae had been observed in dysenteric stool specimens th e E histolytica phenotype was invariably invasive (p < 0.0001). Observ ation of erythrophagocytic amoebae in dysentery is 100% specific and p redictive of infection with invasive E histolytica. When amoebic cultu re-positive cases only are considered it is 96% sensitive. In this stu dy E histolytica of zymodeme XIV was more commonly associated with amo ebic dysentery than zymodeme II. There was no significant difference b etween the carriage rate of invasive and non-invasive E histolytica in non-dysenteric diarrhoea. Asymptomatic subjects carried non-invasive E histolytica more frequently than invasive E histolytica. Patients wi th non-amoebic dysentery, when shown to be infected with E histolytica , carried non-invasive strains (12%). Conclusions-Sensitivity and spec ificity of microscopical examination of a single stool specimen for di agnosing amoebic dysentery is very high; intestinal carriage of invasi ve E histolytica detected by culture is not necessarily an indication of active disease as patients with diarrhoea and asymptomatic subjects shed invasive and non-invasive E histolytica. There are possibly two subpopulations of invasive E histolytica with different pathogenic pot ential which can be differentiated by zymodeme analysis.