Now, a different team of researchers has found another animal harboring the leprosy bacteria: red squirrels in the UK. There hasn't been a leprosy case in the UK in centuries, which had lead to the belief that the disease had been eradicated in the region.
However, researchers at Global Health Institute at the Swiss Federal Institute of Technology examined approximately 110 red squirrels from the UK. Some squirrels displayed symptoms of leprosy while others did not. All squirrels with symptoms tested positive for a strain of bacteria that can cause leprosy in humans. Of those without symptoms, about 20% carried the bacteria.
Based on comparing the pathogen found in squirrels with leprosy found preserved in human remains from the middle ages, the researchers were able to determine a close association with a version of leprosy that circulated widely among people in the region around 1283.
This likely indicates that the pathogen has been harbored by squirrels for hundreds of years -- including the recent centuries in which no cases originating in the UK have been identified. This suggests that squirrels have not been and are unlikely to be a source of transmission to humans.
However, it does point to the possibility that other animals across the world also harbor the disease and may be responsible for the higher rates of transmission seen in other countries.