Are there any good rules on disease in Dark Heresy? I have a situation where the PCs will likely be infected with a deadly disease (knowing their shoot first and ask questions later mentality). Any good home brew?

There's always Nurgle's Rot

Or, the Obliterator Virus I converted from =][= I've linked in my sig

A creative GM could modify the Toxin rules from the GM Screen into good disease rules without too much trouble.

That's how I would do it.

WHFRP also has some nice diseases that converts nicelt to DH.

Yeah, I use the rules from WHFRP for diseases.