I could be mistaken, but I believe that many diseases are regional in severity. For example, FMD was a major deal in Britain and Europe a while back, and although it created a scare here, there was no disease incidence in North America. For world-wide disease, perhaps the World Health Organization would have statistics.
In my area, the biggies are BVD, Rota/ Coronavirus, Hemophilus and I guess E-coli. There are vaccines for all, and antibiotics can work on the latter two, but animals still die from them.