MATERNAL TRANSMISSION OF IMMUNITY TO EIMERIA-MAXIMA - ENZYME-LINKED-IMMUNOSORBENT-ASSAY ANALYSIS OF PROTECTIVE ANTIBODIES INDUCED BY INFECTION

Vaccination of broiler chickens against Eimeria infection is problemat ic because of the need to ensure that birds are protected from the tim e of hatching. We have therefore investigated the feasibility of prote cting hatchling broilers via maternal transfer of protective antibodie s from hens to their offspring. Oral infection of broiler breeder hens with 20,000 sporulated Eimeria maxima oocysts caused production of an tibodies which were passed into the egg yolk and subsequently to hatch lings. The level of specific antibodies in the yolks to unsporulated o ocysts, sporulated oocysts, merozoites, and gametocytes was assessed b y enzyme-linked immunosorbent assays. The Levels in yolks of antibodie s to all developmental stages peaked 3 to 4 Weeks after infection of t he hens. Groups of 10 hatchlings were challenged at 3 days of age by o ral infection with 100 sporulated E. maxima oocysts. In the first expe riment, the mean 4-day (days 6 to 9 post-infection) total number of oo cysts excreted in the feces of chicks from eggs collected 3 weeks afte r infection of the hens was (0.6 +/- 0.4) X 10(6) (mean +/- standard e rror) compared with (9.9 +/- 1.4) X 10(6) for the progeny of uninfecte d hens, which represents a greater than 90% reduction. However, oocyst excretion by chicks from eggs collected 7 or 8 weeks after infection of the hens was only 47 or 68% lower than control values, reflecting d eclining levels of protective antibodies. In a second experiment, in w hich the hens were somewhat older and pretreated by intramuscular inje ction of saline in the emulsifying agent, Arlacel A, the period for wh ich protective antibodies were transferred to hatchlings was prolonged . Thus, oocyst excretion by challenged hatchlings from eggs collected for an 8-week period after infection of the hens was more than 90% low er than oocyst excretion by control chicks, and even hatchlings of egg s collected 19 weeks after infection of the hens showed a 60% reductio n in oocyst output.:In both experiments, the levels of immunoglobulin G (IgG) antibodies to all developmental stages in yolks or hatchling s era were very strongly correlated with maternally derived immunity to E. maxima. In contrast, parasite-specific IgM or IgA was not detectabl e, either in egg yolk or egg white. These results demonstrate the abil ity of IgG antibodies to protect against E. maxima in poultry, thus ra ising the possibility of using protective maternally derived IgG antib odies to identify potentially protective parasite antigens and indicat ing the feasibility of using maternal immunization as a means for para site control.