Re: Mixing Species, or Let's create a novel pathogen!
I don't think the hobby needs to worry about that. People have been in contact with animals for as long as the two have been together and whatever will naturally occur has and will.
In the US we have 20 open trades per year (just throwing out a number) with vendors selling animals from the same original breeding sources.
The worlds wild caught animal markets (for eating or local pet trade) have been an ongoing event every day for hundreds or thousands of years.
I think the likeliness that we unleash a killer virus from our tanks is low to none.
I also keep fish and birds. Lots more sources and mixed wild caught specimens in those than frogs.