Bird flu or otherwise known as avian influenza is caused by a virus found mainly in birds. But it can also infect humans. In fact, there have been more than 200 confirmed cases of human infections since 2004. Most of these cases resulted from close human contact with infected birds. Infected human beings display symptoms such as fever, muscle aches and cough which are typical influenza symptoms. However, they may also suffer from respiratory distress and other such complications.
The virus in question, influenza A, has many subtypes such as H2N2 and H1N1. The current strain that has been spreading is H5N1. Although it spreads quite easily in birds, its still, thankfully, not prevalent among humans. Human to human transmission of this strain are still quite rare though there have been some widely reported cases. In Thailand in 2004, there was a suspected case of human to human transmission between an infected child and her mother. And as recent as 2006 in Indonesia, there was a family of 8 where the virus was suspected to have spread from human to human. Fortunately, the infection was contained within the family and outsiders were not affected. Scientific details on how this virus spreads from person to person are still murky and thus, there are those who question if the virus can indeed spread from one person to another. Though research is being conducted in this area, it may be awhile till we know for sure if human to human to transmission is possible.
There is however a note of concern. Influenza A, being a virus, is capable of mutating. Through a process known as antigenic drift, H5N1 has mutated into various strains, some pathogenic to one species but not affecting others whilst others affect a variety of species. Through such a process, H5N1 might mutate into a strain that easily infects and spreads among humans. That might then cause a worldwide pandemic which would end in the death of up to 150 million humans.