Sorry, a correction - “the disease does not necessarily kill off the host population or it would NOT still be a plague reservoir 100+ years after it (the plague) came here.” I should proofread better, apologies.
True...works the same in a virus like ebola in Africa.
They have found it carried by bats and some primates but it does not kill them very frequently.
My own impression is that it’s carried, like a lot of other diseases by bats, in the case of ebola, but they have yet to prove this.
In any case, the disease ebola or a closely related strain like Marburg has been around for thousands of years, so it cannot be killing the hosts..