There are a lot of points about what diseases could be roaming on that planet but that isn't really any problem nor are things we are immune to a problem.
A few people who replied here have included problems that don't exist in this hypothetical thread!
When there is a place free of a lot of sicknesess plague's and diseases and you were to have all of them you would still go to that planet and possibly infect them with it? While without you there would have never been any problems because you find it unfair not to go?