A longitudinal study of asymptomatic carriers of pathogenic zymodemes of Entamoeba histolytica.

The value of treating subjects who pass Entamoeba histolytica cysts in their faeces is currently in question. In the endemic Durban area iso-enzyme electrophoresis of E. histolytica isolates indicated that 1% of the asymptomatic population are infected with pathogenic zymodemes. The outcome of these potentially invasive infections was established by means of a longitudinal survey. All subjects had strongly positive serological responses--10% of them developed amoebic colitis while the rest remained asymptomatic and spontaneous cure occurred within 1 year. Infections with pathogenic zymodemes occurred in family units and closely related individuals. Since they were cyst passers, good evidence was obtained for the existence of a carrier state for pathogenic E. histolytica. The value of sero-epidemiological surveys in determining the prevalence of pathogenic E. histolytica in a community was highlighted. Treatment of asymptomatic carriers with pathogenic zymodemes of E. histolytica is as essential as treatment of patients with invasive amoebiasis, and in both cases all contacts of affected individuals must also be treated if they are found to harbour pathogenic zymodemes of E. histolytica in order to ensure control of disease transmission.