Circulating antibody response to Eimeria tenella oral and subcutaneous infections in chickens

Immune responses in chickens to Eimeria tenella using oral and subcutaneous routes of infection were investigated. The results obtained indicated that sporulated oocysts inoculated subcutaneously in doses up to 50 000 oocysts per bird were not fatal to 21-day-old chicks. Subcutaneous inoculation of oocysts was found to be less immunogenic than oral administration. The dynamics of the antibody responses were different for the two routes of infection. Orally administered oocysts stimulated a dramatic primary increase in the serum antibody titre with a tendency towards a decrease in the titre 14 days post infection irrespective of second infections at that time. However, a third oral dose of oocysts stimulated a slight increase in antibody titre. Two doses of oocysts injected subcutaneously induced only a slight increase in serum antibody titre. Such a low titre was dramatically increased following a subsequent oral dose of oocysts. Antibodies specific to E. tenella are IgM and IgG immunoglobulins. IgA immunoglobulin was not investigated.