Tracing the strain
Swine flu has spread across the world since emerging in Mexico and is now officially the first flu pandemic for 40 years.
It is a respiratory disease, caused by a strain of the influenza type A virus known as H1N1 and can be spread from person to person by coughing and sneezing.
As cases continue to multiply, Julian O'Halloran investigates the origins of the H1N1 virus and examines claims that it is linked to factory style pig farming in the United States.
Over the past 30 years, pig farming in America has been swamped by industrial scale methods.
Many environmental and animal welfare lobby groups have alleged that this has caused massive damage to the environment, intolerable smells, and health risks to farm workers and their families. They are now asking if it has played a role in the current world flu pandemic.
For years, American virologists have been studying the links between new and potentially risky flu viruses and farm animals.
Experts say that parts of the current flu virus can be traced back to outbreaks of swine flu, then affecting only pigs, in several US states in 1998.
Local people near the first known case in Mexico questioned the role of an American owned pig farm nearby, however this link was strenuously denied and the US pork industry soon helped persuade medical authorities to drop the term 'swine flu' - blaming the use of the term for a sharp drop in sales of pig meat.
With growing alarm and rising death tolls, Julian goes on the trail of the virus's origins, back to an outbreak in pigs in North Carolina, more than ten years ago.