SLS

The name of the sickness from Marble Hornets...

The Slender Sickness is said to be contracted from contact with The Operator. 

I have a personal belief that SLS is also the natural decomposition of a Host over time. 

All Four of them have problems... Braxton and Lydia both have cardiac malfunctions (Like Tim).
While Gina and Andrew have the mental end of the bargain (Like Alex). They both suffer from anxiety, paranoia, and depression to some extent.

As you can see they're all pretty early in the process. And from the Marble Hornets videos, we can tell it takes quite a bit of time to get to a dangerous level. That level being the transformation into a proxy. I've noticed that, in the videos, eventually the coughing stops. Then the technology interference that clings to proxies starts to show up. That usually shows up when sh*t starts to get dangerous. The victim starts to become violent. They may or may not start to see hallucinations. Most are beyond reasoning.

I'm not worried yet... They might be a threat in the future but for now they're my friends.  

-Abyss