Swine flu is a highly contagious respiratory disease that affects pigs. It is caused by one or more subtypes of type A swine flu virus. It is characterized by high morbidity rate and relatively low mortality rate (1-4%) in infected animals. The causative virus spreads among pigs through exposure to infected droplets expelled during breathing, direct and indirect contacts, and symptomless disease carrying pigs.
A pig may be infected by more than one type of the spine flu virus at the same time. This allows for gene unifications that may lead to gene modifications and emergence of new flu viruses including genes from different sources. The different swine flu viruses usually infect pigs, but they may penetrate the barriers separating the different species to infect humans as is the case in the current epidemiology. Once it develops the ability to spread effectively among humans, it may cause a pandemic. It is actually difficult to predict the outcomes of such a pandemic, since the outcomes depend upon many factors, including the severity of the infection, the immunity level, protection produced by acquired antibodies, and factors relative to the host.
Humans usually acquire the disease through direct contact with pigs, but in many cases no evidence of such contact has been traced. Human to human transmission has been recorded but such infections are confined to people with direct contact with infected cases.