This is all above my pray grade but I suspect that is tradition and not commandment.
Now I'll sit back to await my flogging.
The researchers did not find a significant difference in effects from the 1918 and 1930 viruses in infected pigs. This was surprising, since the 1918 virus killed more than 20 million people and was lethal to ferrets, mice and macaques. Another surprising finding from the study was the rapid antibody response in the animals infected with the 1918 virus, which is not typically reported for the swine influenza virus.
This supports the alternate theory that it was not the virus that killed but a co-infection of strep for which we did not have antibiotics in 1918. The strep coinfection would not have occurred in the 1930 cases.
They were unclean under Old Testament law and then were made fit to eat under New Testament law (Peter and the animals lowered on a cloth vision). Not sure why...but, with modern handling methods and cooking, we can eat them without an issue. However, one must remember the disease factor when handling pork.