Various researches consider that the two main events that lead to infection of swine flu in the human beings include firstly the influenza viruses that are the enveloped RNA viruses featured with segmented genome. This further means that the viral RNA code is not the single RNA strand but is available as the 8 different segments of RNA in influenza viruses. As the human virus can actually infect the pig respiratory cell at similar time like the swine virus, some of replicating strands of RNA from human influenza virus can basically get enclosed in the enveloped swine virus by mistake.
The overall amount of RNA kinds in one cell could be 16, like 4 swine and 4 human RNA segments that can be included into one single particle. The different blends of RNA segments can then result in new subtype of influenza virus that can have the capacity to infect humans but highlight the characteristics that are excusive to swine influenza virus infection. It is also possible to incorporate the RNA strands from swine, human and bird influenza viruses into a single virus in case the cell becomes all infected with three kinds of influenza. Formation of the all new viral kinds is taken to be the antigenic shift, tiny changes in the particular RNA segments in the flu viruses are known as antigenic drift thereby resulting in minor alterations in virus.
Second, the pigs can play exclusive role as intermediary host to latest flu kinds as the pig respiratory cells may be infected directly with the human, bird or other flu viruses. Also, the pig respiratory cells are capable enough to get infected with various types of the flu and may function as the mixing pot for RNA flu segments. The pigs may pick such viruses from environment and tend to be the main method that the bird virus RNA segments go into the mammalian flu population.