Jeff,

As (IIUC), diseases are a mainly biochemical thing, maybe look towards
that direction for inspiration?

Frinstance, if two given human races are mutually interfertile, then
diseases could (probably) jump back and forth with little issue.

Further along that paradigm, the more similar analogous
systems/structures are, the lower the biochemical barrier would be.  For
example, various types of encephalitis would probably be a threat to
most sapient mammals.

As for to and between non-humans of Terran origin,hmm... I could see
Vargr (being uplifted wolves) having to worry about (variants of) canine
distemper.

Non-Terran non-humans is a heck of a lot harder to prognosticate about -
maybe (as a supposition) the small fraction of diseases that can cross
over between a given pair of such (or between one such and humaniti)
makes everyone very happy it's just a small fraction?

A la the Deathworlders universe, where humans and domestic cats are two
of the deadliest known predator species in that universe's Milky Way
galaxy, having evolved on the bioweapon lab known as Earth and got their
practice wailing on each other.  Most human diseases can't jump to other
species, but the ones that do are hellish.  Cat dander seems to be a
biological/chemical weapon.

Alex

On 22/3/20 9:43 am, Jeff Zeitlin wrote:

> <snippage>
>
> * To what extent do human diseases cross between any of the major human
>   racial goups, or between them and the more extreme minor-racial variants?
>   What about to non-humans of Terrestrial origin (e.g., Dolphins, Vargr,
>   uplifts)? What about to non-humans of non-Terrestrial origin (e.g.,
>   Virushi, Llellewyloly, Bawapakerwa-a-a-awapawab) or of geneered mix
>   (e.g., Luriani)? What about the reverse - minor-racial diseases crossing
>   into major human racial groups?
>
> <snippage>
--