PIR and infection: Pir genes of the S7 clade within particular loci called acute-associated loci (AAPLs) are more highly expressed in the acute-phase of infection and are associated with avirulent infection, whereas a more restricted number of pirs from the L1 clade that are associated with the chronic-associated loci (ChAPLs) are highly transcribed during the chronic-phase of infection and are associated with a more virulent course of infection (Brugat et al., 2017).