Cold prohibits growth
Hot promotes growth.
Bacteria cause disease and need heat to live
Viruses cause disease and heat.........do viruses spread the same rate in cold conditions as warm?
Ok, some viruses have evolved for colder temps and some for warmer, but the ways the ones for colder temperatures evolved was to form a icey coat around it so it can survive longer in the cold temperature, then once it makes itself into someone's body, the coat melts from the heat and it does its job. (check here for more details)
This shows that both need a warm environment to grow. because they grow from hijacking the DNA of something that does need warm temps to grow. They cannot be anything more than a slightly better or worse version of whoever they hijack.
That is some crazy sci-fi shit right there!!