An epidemiological study of Entamoeba histolytica and Entamoeba dispar infection using polymerase chain reaction

Abstract

The recent discovery of the existence of Entamoeba dispar (E.dispar) as an amoeba that is constitutively nonpathogenic but morphologically indistinguishable from Entamoeba histolytica (E.histolytica), has raised the question of the validity of most epidemiological studies on amoebiasis. This study was conducted in two villages. The presence of amoeba was determined by microscopic examination of fresh stools and formalin-ether-concentrated specimens. An improved colorimetric 'polymerase chain reaction' (PCR) method was used and ELISA assay was used to detect anti-E.histolytica antibodies in the serum samples. The combined frequencies of E.histolytica/E.dispar according to stool microscopy were 35% in village A, and 28% in village B. According to PCR results, E.histolytica was not detected and E.dispar was found in 21% and 18% of stool samples in A and B villages respectively. Thirty-five percent (92/260) of the sera reacted with E.histolytica antigen and 28% (72/260) of the sera reacted with E.dispar antigen. A correlation between antibody levels and the presence of E.histolytica/E.dispar in stool microscopy could not be detected. A significant correlation was found between antibody responses to E.dispar and E.histolytica antigen (p=0.001). According to our results, the prevalence of E.histolytica in our area seems to be very low. Serology is not helpful in distinguishing E.histolytica from E.dispar in asymptomatic cyst passers in an endemic area.