Strikingly, the protection conferred against M. robertsii by the prior ingestion of PAO1 was abolished in the ΔPPO1-ΔPPO2 and Hayan mutants (Fig 5D and 5E), but not in the Sp7 mutants (Fig 5F), even though the latter are much more sensitive than Hayan to the PAO1 latent infection protocol (Fig 3C). This evidence concerns the gene SP7 and disease arising from reactivation of latent virus.