Indeed an increase in mucus secretion is a characteristic feature of AGD, and although the fold changes were modest, the increase in the expression of several mucin protein isoforms observed in this study may pre-empt much larger expression increases at later stages of infection as suggested by results obtained from a genomic study showing up-regulation of mucin gene expression at 14 and 21 dpi [18]. This evidence concerns the gene MUC5AC and infection.