A process in which a symbiont interferes with, inhibits or disrupt a JAK-STAT signal cascade in the host organism by reducing the activity of host IRF9 (interferon regulatory factor-9), a transcription factor involved in the innate immune response. For example, viral infection triggers binding of IRF9 to phosphorylated STAT1 and STAT2, forming the ISGF3 complex. The ISGF3 complex migrates to the nucleus and activates transcription of IFN-responsive genes.
disruption by virus of host JAK-STAT cascade via inhibition of host IRF9 activity