Some species don’t easily cross-over to humans, and in fact most diseases don’t easily cross-over (influenza and SIV are major exceptions but the pattern is that cross-over is itself pretty rare). We could maybe look at species which don’t cross-over to humans due to much different biology, like say in cephalopods. I’m not sure we know enough about disease in such species though, or that they are similar enough to mammals to be a useful comparison.
Some species don’t easily cross-over to humans, and in fact most diseases don’t easily cross-over (influenza and SIV are major exceptions but the pattern is that cross-over is itself pretty rare). We could maybe look at species which don’t cross-over to humans due to much different biology, like say in cephalopods. I’m not sure we know enough about disease in such species though, or that they are similar enough to mammals to be a useful comparison.