When there was a plague in Surat, did you catch all the rats and test them? Did you study them for the virus that carried the plague and killed those who had it? And let go those rats who, as impossible as it may seem, did not carry the disease. No! You just went ahead killed all the rats. Even if there was a rat which did play host to the virus, it got killed – just because it was a rat. That’s how things work.
Many thanks to Mr. Promod Mutalik for providing the germ of the analogy. (no pun intended)