Globalisation and industrialisation are causing diseases to spread from humans to animals, a study has shown.
Researchers from The Roslin Institute of the University of Edinburgh have shown that a strain of bacteria has jumped from humans to chickens.
It is believed to be the first clear evidence of bacterial pathogens crossing over from humans to animals and then spreading since animals were first domesticated some 10,000 years ago.
The study identified a form of the bacteria Staphylococcus aureus - of which MRSA is a subtype - in chickens, and found that the bacteria originally came from humans.
Genetic testing showed that the bacteria crossed over from one species to another around 40 years ago, coinciding with a move towards intensive poultry farming practices.