Swine flu is a respiratory disease, caused by a strain of the influenza type A virus known as H1N1. H1N1 is the same strain which causes normal seasonal outbreaks of flu in humans on a regular basis. Seasonal influenza viruses circulate continually among human populations and despite the use of vaccines they are responsible for illness and deaths every year, particularly among people who are immune-compromised, or have underlying health problems.
Influenza viruses also circulate continuously among animals, especially birds, and whilst they may pose a theoretical threat to humans, they normally only lead to isolated, sporadic human infection (usually as a result of close direct contact or through faecal matter) and do not develop the ability for human to human transmission.
However, the concern for health experts is that a new influenza type virus, originating from animals, does develop the potential to spread from human to human and with little or no immunity present in the population, spreads rapidly until appropriate vaccines are created and made available.
This latest version of H1N1 is different from what we have previously encountered in that it contains genetic material that is typically found in strains of the virus that affect birds and swine, as well as humans. Although this strain may have originated in pigs, it had the ability for human to human transmission and is now a wholly human disease.
According to the World Health Organization: “This is a new influenza A (H1N1) virus that has never before circulated among humans. This virus is not related to previous or current human seasonal influenza viruses....most people have no or little immunity and, therefore, this virus could cause more infections than are seen with seasonal flu....With the increase in global transport, as well as urbanization and overcrowded conditions in some areas, epidemics due to a new influenza virus are likely to take hold around the world, and become a pandemic faster than before.”
The European Centre for Disease Prevention and Control (ECDC) explain that the present influenza A (H1N1) virus “contains segments of genes from pig, bird and human influenza viruses in a combination that has never been observed before anywhere in the world”.