SLC20A1 and infection: Two subtypes of KoRV (KoRV-A and KoRV-B/KoRV-J) are now recognised, as defined by sequence differences and by the cellular receptor used during infection [30]: KoRV-A uses the sodium-dependent phosphate transporter encoded by the Pit-1 (SLC20A1) gene [31], whereas KoRV-B uses the thiamine transporter encoded by the THTR1 (SLC19A2) gene [25, 32].