maxima APGA could induce cross-protection

to heterologous species, E. tenella and E. acervulina, as well as E. maxima infections (68,69). At this point, it was believed that this cross-reactivity was most probably due to conserved epitopes of the major gametocyte antigens in the different species and, thus, led to the hypothesis that a vaccine of E. maxima gametocyte antigens could possibly be used to control coccidiosis caused by at least the three predominant Eimeria species. In floor pen maternal immunization trials, the resistance of chicks from APGA-immunized breeder hens was compared to that of hatchlings from control parent flocks by introducing oocysts to the pens via infection of ‘seeder’ birds infected with 50 oocysts of E. maxima, Maraviroc E. tenella and E. acervulina. Analogous to the laboratory trials, a reduction of 60–80% in oocyst shedding into the litter was observed; comparable to the reduction observed using coccidiostats (59). These Staurosporine trials were repeated three times under the same conditions, showing that there was an average reduction of 60–70% oocyst output in vaccinated groups up to 4–6 weeks in age (59,70). These results were encouraging, as they supported the idea that the highly conserved E. maxima antigens could provide good levels of protective immunity against at least three major species

that cause coccidiosis in broilers. Despite this, questions still remained about whether this vaccine could provide maternal protection against all Eimeria species (and strains) encountered in the field and if maternal immunity was applicable in controlling coccidiosis

within industry management schemes and climatic conditions. To further assess the efficacy of maternal immunization with APGA, testing was undertaken in a multi-centred, multinational field trial involving five countries from four different continents: Israel, Brazil, Argentina, South Africa and Thailand (71,72). The safety and immunogenicity of the vaccine in breeding hens were assessed on a large scale, with birds vaccinated twice prior to the start of their laying period (15 and 20 weeks respectively). Immunizations were found to have no deleterious effect on the hens (72): no adverse reactions; no damage at the site of injection; and no affect on hen mortality or on the number before of eggs produced (e.g., in the Argentine trials, 119 eggs were produced per immunized hen vs. 116 per control hen). In all four countries, IgG antibody titres remained at a presumptive protective level throughout the life of the laying hens. The maintenance of highly specific IgG antibody levels in vaccinated flocks is thought to be due to the boosting effect that is naturally acquired from exposure to infection with oocysts in the environment (72). It is even conceivable that maternal antibodies may increase due to this natural exposure. However, in the absence of immunization, these titres are variable and, therefore, do not necessarily provide protective levels of maternal immunity (72).