From the text:" One of their difficulties is that the large, complex DNA virus that causes African swine fever has some 170 genes and 80 proteins, many of them specialized in evading different aspects of the pig immune system. "

So it is evolution, probably facilitated by certain conditions.

A huge amount of genes is also a weakness and might be targetted with specialized measures (like a proteine/gene-blocker). But the usual tricks wont work as well.