The present invention concerns a use of strains of Toxoplasma gondii having at least an adhesin MIC-1 and/or an adhesin MIC-3 inactivated by a genetic modification relating to at least one of the mic-1 and/or mic-3 genes, in the preparation of a medicament for preventing or treating cryptosporidiosis associated with Cryptosporidium parvum in a neonate mammal in need thereof.