Observations on the interpretation of amoebic serology in endemic areas

Antibody to Entamoeba histolytica antigen was evaluated in cases of proven and suspected intestinal amoebiasis as well as in extra-intestinal cases from an endemic area. Screening methods included the gel diffusion precipitation test (GD), counter immunoelectrophoresis (CIE) and the indirect haemagglutination test (IHA). Control populations consisting of asymptomatic cyst passers, non-amoebic individuals, patients with giardiasis and cases of enteric fever were also screened using the above tests. All (100%) cases of amoebic liver abscess and 75-80% of hepatic amoebiasis without overt abscess formation could be detected by serology, with good correlation between the tests used. However, the interpretation of serology in cases of proven and suspected intestinal amoebiasis posed two main problems. The presence of low antibody levels even in proven cases and the persistence of antibodies due to past infection was found to reduce the diagnostic efficiency of serology for acute intestinal amoebiasis. There was no statistical difference between intestinal cases and controls when comparing either percentage of cases detected or titre of antibody obtained. The results of this study indicate that serology for acute intestinal amoebiasis can be unreliable; however, it is of undoubted value as an adjunct to clinical diagnosis in cases of hepatic amoebiasis.