The present invention relates to an isolated polypeptide which has sialidase activity, selected from the group consisting of: (a) a polypeptide which has an amino acid sequence which has at least 60% amino acid sequence identity with amino acids 1 to 407 of SEQ ID NO: 3; (b) a polypeptide which is encoded by a polynucleotide which hybridizes under low stringency conditions with (i) the nucleic acid sequence of SEQ ID NO: 1 or 2 which is at least 80% or 90% identical over 60, preferably over 100 nucleotides, more preferably at least 90% identical over 200 nucleotides, or (ii) a nucleic acid sequence complementary to the nucleic acid sequence of SEQ ID NO: 1 or 2.