I can't prove it, but I think that the primary cause for the population explosion is that somehow feral hog populations developed an immunity to hog cholera.
In the late 1960s and early 1970s, I worked for Texas Agricultural Experiment Station--mostly in south Texas, but also for a couple of years in east Texas. At that time, feral hogs were not really abundant anywhere. Most of them in east Texas were ear-marked, meaning that they had been trapped and marked by someone who claimed ownership. In the early fall, hog traps would be set up and baited. The shoats that were captured would be earmarked and the adults culled for winter meat. It was unusual to encounter an adult hog "in the wild" that was not earmarked.
During this time feral hog populations in south Texas waxed and waned in a "boom and bust" cycle. They would get abundant everywhere for a two or three years, then hog cholera would spread through the populations like wildfire. After the resultant die-off, there wouldn't be many hogs anywhere for another few years, until the populations rebounded. These "boom and bust" population cycles were well documented.
I left Texas in 1977 for a job at Kansas State University, then subsequently worked in Nebraska for a few years. I went back to the Texas and worked for the General Land Office for a few years in the mid-1980s and then left again for a job in Colorado. I think that feral hogs in south Texas has begun to be a problem by about that time, but my responsibilities were with the management of State Lands in far west Texas, so hogs weren't really on my radar.
By 1990, articles about the "scourge' of feral hogs had started to appear in the technical literature. I spent several years reading these accounts, but I naively assumed that hog cholera would eventually make a comeback and the problem would subside until the next population "boom." As as often been the case, I was wrong.
After a few more years, I started corresponding with wildlife biologists in Texas with whom I had worked, and I realized that the "boom and bust" cycles were a thing of the past. Since then, I have made several abortive attempts to try and pinpoint when, where and how hog cholera had no longer become the factor controlling populations of feral hogs. However, I had a job that was more than full-time, so I never was able to even figure out exactly where to start. I figured that I would get back to it when I "retired", but my retirement years have been spent doing consulting on other natural resource issues and solutions outside of Texas, so I am no more knowledgeable about the subject now than I was 15 or so years ago.
Nonetheless, I am convinced that somewhere, somehow, feral hogs developed an immunity to hog cholera--one that could be genetically passed on--and I believe that is what has led to the problems that plague us today
