The term symbiosis needs to more explicitly cover distant relationships - such as between human and strawberry. Predation and some forms of direct competition such as combat should probably be included.
We need a term for the start of a symbiosis. Symbiogenesis should probably be that term. Most attempts at a current definition of that term appear to be a mess.
We need a term for a symbiosis that forms a functional organism - such as a Portuguese Man o'War. I propose "symbiorganism". The term "symbiome" has been previously used in this context - but it doesn't seem up to the job to me.
"Transmissible" and "transmissibility" are quite a mouthful and is even worse. "Infectious"/"infectiousness" and "virulent"/"virulence" are pretty parasite-specific. It isn't clear what to do about this. Perhaps we could use "spreadable" and "spreadability".