Observations on the duration of the acquired immunity of chickens to Eimeria maxima Tyzzer, 1929

Young chickens given an infection of 5000 oocysts of E. maxima were highly resistant when they were given a 2nd dose 3 weeks later. Immunity in these fowls was not apparent when they were again infected 10 weeks after the 2nd infection. The same fowls given a final dose 26 weeks after the 3rd infection became heavily infected. These observations suggest that immunity developed to this infection is short-lived, and this finding is discussed in relation to the duration of acquired immunity to E. tenella infection in the fowl and E. stiedae infection in the rabbit.