Make Biology Great Again 2
Stealing blatantly from guns, germs and steel when I say this, but bacteria and viruses have been a pretty useful weapon and tool in colonial enterprises, both intentionally and unintentionally
I think this could be implemented in three steps
Biological Similarity
We already have stats about gravitational preferences, temp preferences etc, which are essentially descriptions of biological requirements.
Using these a similarly score from 0 - 1 could be made, with two species with identical colonisation preferences sitting at 1.
Diseases cannot pass between sufficiently different species (say, 0.8), but, if you bring your dirty humans onto a planet of near-humans, expect there to be transition between the populations
Disease severity could be more-or-less random, but should decrease over time. The new population would eventually be carriers (I.e. asymptomatic yet infectious).
Therefore, if species a carries disease x to species b, species b will eventually also be able to infect species c with disease x
Passive infection
If a diseases jumps from one species to another, we could expect unrest and reduced population growth. Severe diseases could send a population into decline
Obviously genetic centres can protect populations from this effect and bring about immunity far faster
Active infection
Bioweapons are actively engineered versions of the passive infections, with enhanced transmissibility / lethality /resistance to immunity (researched in biology)
Can be designed to target species with certain habitability preferences, so you could infect a group very different from yours and put yours at no risk
Conclusion
Have more thoughts on the details but first and foremost wanted to hear if this was an interesting idea or a bit too grim?
I hope, however, that this would bring the long-neglected field of biology into the limelight!