IgG antibody response to ES or somatic antigens of Dicrocoelium dendriticum (Trematoda) in experimentally infected sheep

The ELISA technique was used to study the kinetics of IgG antibodies against excretory-secretory (ES) and somatic (So) antigens of Dicrocoelium dendriticum in the sera of 32 lambs: 12 experimentally infected with 1,000 metacercariae, 12 with 3,000 and 8 controls. Both antigen types were used at a 2 mu g/ml concentration. Dilutions of sera and the anti-sheep IgG peroxidase conjugate were: 1:200 and 1:6,000, respectively. Optical density values for each type of antigen in the two infected groups were higher than the cut-off point from day 30 post infection (p.i.), showing positive infection. Maximum antibody levels were observed 60 days p.i. and remained high until the experiment ended 180 days p.i. This pattern was similar for both ES and So antigens, although with slightly lower figures in the latter. Antibody kinetics were very similar for each of the two doses, except on day 30 p.i. No correlation between the antibody level and parasite burden could be established.