Swine influenzas epidemics are actually caused by several strains, spreading across swines populations with more or less visible symptoms. The Swine influenzas are likely to have existed for thousands of years, probably millions, coevolving together with swine immune system as a traditional arms race opposing them too.
In human farms, swine influenzas are likely to have caused difficulties since the beginning of swine taming, in terms of productivity, as well as in term of rare interspecies virus transmissions. That's only in recent centuries, and especially in recent decades, that humans got the knowledge need to record, study, understand and soon create vaccines and look at the genetic code of swine flus.
The first isolation occurring in 1930. The swine flus have been mainly an economic concern, especially within intensive pig farms (pork industry) which increasingly looked for ways to keep their herds alive, healthy, and growing faster
