Two serological tests--the virus-neutralization (VN) test in chicken embryo fibroblasts (CEF) using a cell-culture-adapted virus, and the
enzyme-linked
immunosorbent assay (ELISA)--were used for evaluating the immune response in chickens against fowlpox virus. The VN test was conducted in 96-well tissue-culture plates using a fowlpox virus that was adapted to induce cytopathic effects (CPE) in CEF in 48 hr. The ELISA was carried out with an
antigen prepared by precipitation of a cell-culture-propagated virus
suspension with
ammonium sulfate and concentration by centrifugation. A 0.1 M
acetate buffer, pH 5, was used as the sensitizing
solution for maximum specific binding of the
antigen to the microplate
plastic well. No
antibodies were detected by the VN test in 228 serum samples taken from chickens at irregular intervals between 1 and 39 weeks of age, even though the birds were vaccinated against
fowlpox at 13 weeks of age. However, in sera collected 4 weeks after a sample of laying hens was challenged with fowlpox virus, VN titers of 1/10 to 1/40 were detectable. On the other hand, significant antibody reactions were detected by the ELISA on sera from chickens during the growing period, following vaccination and challenge. Although no maternal
antibodies were found at 1 week of age, a continuous increase in the mean ELISA titers to
fowlpox was demonstrated during the entire experimental period. This study showed that the ELISA was considerably more sensitive and practical than the VN test.