Imma Perfetto
Cosmos science journalist
Genetic evidence from long-dead squirrels has re-written our understanding of the history of leprosy.
New archaeological evidence from the medieval city of Winchester shows that English red squirrels were once infected with strains of Mycobacterium leprae, which causes leprosy in people.
“The history of leprosy is far more complex than previously thought,” says Verena Schuenemann of the University of Basel in Switzerland, senior author of a report in the journal Current Biology.
“With our genetic analysis we were able to identify red squirrels as the first ancient animal host of leprosy.”
Leprosy is one of the oldest recorded diseases in human history. It remains prevalent today in Asia, Africa, and South America with more than 200,000 cases reported each year.
Chronic infection in humans can lead to nerve damage, blindness, loss of smell, hair loss, dry skin, and lesions.
Scientists have traced the evolutionary history of M. leprae before, but Schuenemann says there has been no consideration of the role that animals might have played in the transmission and spread of the disease in the past.
“As such, our understanding of leprosy’s history is incomplete until these hosts are considered,” says Schuenemann.
To investigate historic interspecies transmission of leprosy, the researchers studied 25 human and 12 squirrel samples dating to between the 11th and 15th centuries.
The city of Winchester was chosen for its historical connection to the fur trade, as squirrel fur was widely used to trim and line garments in the Middle Ages. It also contains the site of one of the best-studied leprosaria – places to isolate and care for lepers – in the country.
The researchers sequenced and reconstructed four genomes representing medieval strains of M. leprae, including one from a red squirrel.
“The medieval red squirrel strain we recovered is more closely related to medieval human strains from the same city than to strains isolated from infected modern red squirrels,” says Schuenemann.
“Overall, our results point to an independent circulation of M. leprae strains between humans and red squirrels during the Medieval Period.
“This finding is relevant to today as animal hosts are still not considered, even though they may be significant in terms of understanding the disease’s contemporary persistence despite attempts at eradication.”
Today M. leprae is known to infect wild armadillos in the Americas, wild chimpanzees in West Africa, and red squirrels from Brownsea Island in the county of Dorset, England.
Greater insight into animal hosts’ contributions to the transmission of leprosy is essential to one day eradicating it.
