It’s damn effective, harder to believe pain is felt by most (all?) animals than that it isn’t. The default assumption should be that they feel pain, not that they don’t.
I think creatures that don't feel pain would not survive long in the wild. If they don't feel pain they would not have any reason for avoiding dangerous situations.
Viruses and bacteria avoid harm and death if they can help it, but that doesn't necessarily mean they can "feel pain".