The present invention relates to an active polypeptide comprising the amino acid sequence of SEQ ID NO: 3, or having at least 50%, preferably 70%, more preferably 90% identity with the amino acid sequence of SEQ ID NO: 3, or fragments thereof having at least 21 contiguous amino acids, or peptides having at least 50%, preferably 70%, more preferably 90% identity with the amino acid sequence of said fragments, provided that said polypeptide is not SEQ ID NO : 2, variants and antigenic fragments thereof, SEQ ID NO 16 or SEQ ID NO 17.