What is the Rot?

Canon Information:

TAPE 4: BROADCAST ANOMALIES - WELCOME TO GLOAMING COUNTY
How to protect yourself from the Rot
1. Identify the threat (a glitched image of a deer is shown)
2. Isolate (a glitched image of a deer is shown)
3. Exterminate (a glitched image of fire is shown)
4. Defend your land (regular image of guard dog and gun are shown)
There is a State Quarantine. (this is likely due to the rot)
Images that Flash on screen after the protect yourself segement