So what's the difference between "highly contagious" and "highly infectious", as the CDC ascribes to leprosy?
This CDC summary doesn't say anything about "highly infectious". It's bacterial, yet they've NEVER managed to get it to grow outside a living animal, so you can be pretty sure it's not growing on public toilet seats. Transmission is difficult (a lot like getting warts) and appears to require prolonged exposure. And about 95% people are flat-out immune to it (i.e. they can get technically "infected", but will never develop any symptoms of the disease). It is curable, but that takes a long time. Making it go dormant (and thus non-transmissable) is much quicker (about 3 months).