mutation depends on the human body containing the virus. the virus does not mutate outside an infected body. therefore terrian will have no effect on mutation. and the mutation is done. human-human flu exists in vietnam. the vietnamese strain is also resistant to treatment and is liable to infect more while still keeping a very high mortality rate.

and breeding of the virus also occours within the body and so is totally seperate from the climate in the same way terrain is. unless you meant of the bodies containg it but i can't see the relevance of that.