Class-specific antibody responses in pigs following immunization and challenge with sporocysts of Sarcocystis miescheriana.

Sixteen pigs were each immunized by oral inoculation with 1000 sporocysts of Sarcocystis miescheriana at 8 weeks of age. Four equal groups were then challenged with 3 million sporocysts per animal at 40, 80, 120 or 160 days post-immunization (dpi). Host antibody responses were monitored using the enzyme-linked immunosorbent assay (ELISA) and the indirect fluorescent-antibody test (IFAT). When using class-specific ELISAs, dramatic increases in specific IgM-antibodies were observed at 21 dpi and increasing levels of IgG-antibodies were detected at 34 dpi. IgM-antibody titres dropped relatively quickly to insignificant levels, whereas IgG-antibody titres persisted at high levels until the end of the experiment. Following challenge, elevated levels of IgM-antibodies were detected, whereas IgG-antibody titres remained unchanged. The dynamics of the antibody titres detected by the IgG-IFAT closely corresponded to those detected by the IgG-ELISA. Despite the presence of specific antibodies at the time of challenge and the continued production of IgM-antibodies after challenge, the protective immunity decreased after 40 dpi and had disappeared by 120 dpi. Furthermore, none of the techniques used were suitable for the detection of specific antibodies during the early phase of acute sarcocystosis around 12 days after challenge.