The invention relates to a novel oocyst sporocyst protein (EtOs22) belonging to the parasite of the species Eimeria tenella and to the polynucleotide encoding this protein, to vectors which contain this polynucleotide, to cells which are transformed with these vectors, to antibodies which are directed against the protein, to vaccines which comprise the polynucleotide, the protein, or fragments thereof, the abovementioned vectors or antibodies directed against the protein, and to the use of polynucleotide or of polypeptide for finding active compounds for treating an infection with Eimeria and active compounds which are suitable for the therapy of an infection with Eimeria.