Serological differentiation between past and present infection in hepatic amoebiasis

The indirect fluorescent antibody (IFA) test and the amoebic gel diffusion (AGD) test were assessed as tools for differentiating between past and present infection in invasive amoebiasis; in the case of the IFA test the Entamoeba histolytica-specific IgG and IgM were monitored. In a pilot study in which sera from 56 patients with suspected invasive amoebiasis were tested the IgM was positive in 40% of confirmed intestinal and 83% of confirmed hepatic cases, the IgG and AGD were positive in all confirmed cases. A subsequent study was then carried out, in which the tests were used to monitor longitudinally antibody levels of patients with confirmed amoebic liver abscess, from the time of admission to hospital, to one year after successful treatment. The specific IgM levels became negative sooner than the IgG or AGD, with more than half the subjects giving negative results at six months and all cases becoming negative 46 weeks after treatment. The results of this study suggest that the presence of specific IgM, together with specific IgG and a strongly positive AGD test, is indicative of an active infection; conversely, when the IgM is negative, while the other tests are positive, active disease was usually absent.