Distribution of antigens of Fasciola gigantica at various stages of development.

An indirect immunofluorescent antibody test on the serum of a Fasciola gigantica-infected rabbit, showed specific fluorescence on the tegumental surface of miracidia, sporocysts, rediae, cercariae, metacercariae and juvenile worms aged between one and seven weeks. The same reaction occurred in the gut cells of cercariae and metacercariae and in the gut caeca of juveniles in the liver. The results of the absorption test indicated that stage-specific antigen(s) in metacercariae and seven-week-old worms existed mainly in the gut cells and the gut caeca, respectively. The precipitating antibody reacting to metacercariae antigens occurred at a very early stage of infection, but the titre dropped much earlier than that against the juvenile antigen.