The use of cyst antigen in the serodiagnosis of amoebiasis.

The choice of a specific and pure antigen is one of the many problems in the serodiagnosis of amoebic infection. Microbial associates in amoebic cultures have often given rise to confusing results in these tests. Entamoeba histolytica trophozoites grown axenically provide a useful source of antigen but the axenic medium is expensive and cumbersome to prepare.The authors have successfully investigated the use of E. invadens cysts as a relatively inexpensive source of bacteria-free antigen which can be employed in routine diagnostic work. Indirect haemagglutination tests using the easily prepared cyst antigen show remarkable sensitivity and reproducibility in detecting anti-amoebic antibody levels in patients suffering from amoebiasis. The cyst antigen appears to be superior to E. histolytica trophozoite antigen in detecting cases of acute amoebic dysentery.