Thinking symbolically, a plague sneaks up on people, one at a time, but with a networked approach. The hosts perpetuate it.
Communicable disease leaves people feeling helpless, disappointed in their inability to function, worn out, fearful of how long it will last. The disease germs are invisible, but take over so quickly, and are sometimes killed off without active intervention. Our bodies can fight some, medications and medical staff can take care of others, but there are also fatal plagues that people give up on.
There is also the unclean feeling that might not be in similar dreams. In ability to wash off the evidence or influence... feeling like something bad got under your skin.
If you think this might parallel something in your life, think affliction, loss of tangible control, spread from person to person through contact.
If it related to the church, it might be an unhealthy teaching or mindset that people take on.
If related to work, it might be talk of pink slips and budget cuts throughout every department.
If social, it might feel like too many people were taking on bad practices, vices, backbiting, or attitudes, and it was distorting who they really were. I feel plagued when I flip channels past those dating shows where people try different partners and then insult the ones who lost. The scum attitudes in society don't just sit in a puddle -- they breed. Hosts (people) take them on and incubate the germs, then spread them.