I always assumed that just like they search for the formulae that represent matter, they also search for formulae to tear it apart. I figured that Bio, Miasma etc were just formulas that deconstruct the body from within, causing harm to the target over time, until the spell has no more go-power and the aetherically-summoned "virus" ceases. So you enact a mathematical formula that doesn't actually "infect" your opponent, per se, but wracks them with a slowly growing destruction from the inside out, as their tissues unwrite themselves.

I guess it makes sense from a more fluff-based perspective. Each of the different spells [Miasma, Bio, Virus] target a different part of the enemy. That cell destruction causes them harm until the spell itself wears off and/or their bodies are mended.