Influenza A strains (of which the so-called "bird flu" is one) are constantly circulating between birds, swine, and humans. So yes, strains of influenza A may originate in pigs and then be transmitted to birds. However, new strains generally begin in birds and then travel to pigs and humans. This is because, of the different types of antigens that may be found on the outside of the virus particle, there is the greatest number of different antigens circulating in the bird population.
That the H5N1 strain is now being found in pigs indicates that the strain is increasing in its capacity to jump species. The close interaction of birds, swine, and humans that often occurs in various places in Asia is the reason that the pandemic influenza strains almost always originate in Asia.
Thanks....I think.