It's an electrified plasma cannon. It fires a charged bolt of energy. I found that the Veronica virus responds very poorly to electricity-- the current can disrupt the virus' natural regenerative abilities, which causes the virus to fly into overdrive trying to compensate. This results in a massive, uncontrolled mutation that can end in the organism exploding, or at least enough important parts of it being damaged that it dies.

It's... messy.

I found, though, that a mild electrical current interrupts the regeneration without triggering that defense mechanism. Then a suppressant can be injected that will stop the virus' progress. That was what we were trying to do to save the boy when... something went wrong.