As I understand it deer655, there are a number of factors involved. First off, there are several strains of the epizootic hemorrhagic disease virus. I guess that, like many viruses, it can mutate over time. Second, the virus is transmitted to deer by gnats which are worse when there's a rainy spring followed by a dry summer. Then, the scientist say that that the deer that survive the disease develop resistance to it and pass on that resistance to their offspring. But I suspect that fades over generations and/or may not protect them from a different strain.

Last year we had the warmest winter in years. I don't think it got below freezing more than a half dozen nights over the course of the winter. At no time did we have freeze levels during daytime hours. I'm sure that was a factor for us.