Worliczek et al. [41] demonstrated an antigen-specific IFN-ɣ response of splenocytes from weaners upon challenge, and Schwarz et al. [29] showed an increase of specific antibodies in blood serum and colostrum of pregnant sows after high-dosed infections, indicating that the infection of immune-competent animals can induce an immune response, despite the absence of oocyst shedding [29, 41]. Here, IFNA1 is linked to infection.