Medieval Mystery Solved: Red Squirrels Likely Source of Leprosy in England

Researchers discovered leprosy-causing germs in people's DNA, as well as a red squirrel found in medieval UK locations, shedding light on the disease's spread.

Scientists found leprosy-causing Mycobacterium leprae in UK red squirrels (Sciurus vulgaris) in 2016. Some strains matched those discovered in humans living in England 700 years ago, per Gizmodo.

Based on this discovery, Sarah Inskip and her University of Leicester team investigated 25 skeletons from a medieval leprosy hospital site in Winchester and 12 red squirrels from a local fur business from the 11th to 13th centuries.

Here's What Experts Discovered

Most human bones had leprosy-like lesions, whereas squirrel bones showed inflammation, suggesting the condition. After a genetic examination of the bones, M. leprae DNA was found in three humans and one red squirrel, making it the first non-human carrier of leprosy.

The three medieval humans and the medieval red squirrel's M. leprae strain were more closely related than they are to modern red squirrels, suggesting a transfer between squirrels and humans in medieval England.

Medieval Winchester's leprosy hospital, fur trade, and squirrel pets allowed transmission, according to Verena Schünemann of the University of Basel, Switzerland.

Modern squirrel leprosy strains and medieval specimens may be unrelated, suggesting multiple transmission episodes between humans and squirrels.

According to former US Public Health Service official Richard Truman, certain present red squirrel populations contain leprosy, although the danger of transmission to people is low, underscoring the need to understand M. leprae's ecological history.

Today, few people are vulnerable to leprosy, and prolonged contact with an infected animal is needed to get infected, according to Dr. Sarah Inskip.

Britain's natural red squirrel population is just 160,000, limiting the risk of illness.

(Photo: Jeff J Mitchell/Getty Images) A red squirrel feeds in the Trosssachs on September 28, 2018 in Aberfoyle, Scotland.

The crew investigated Winchester's St. Mary Magdalen's leprosarium, a medieval leprosy hospital. Their investigation established a link between red squirrels and human strains.

Modern Red Squirrels Are Safe

Senior author Verena Schuenemann, an archaeologist at the University of Basel in Switzerland, told Cell, "With our genetic analysis, we were able to identify red squirrels as the first ancient animal host of leprosy."

As per a New Scientist report, she said that medieval red squirrel disease is genetically closer to Winchester's medieval population than current red squirrels.

Schuenemann and her team, who investigate ancient pathogen genomes, found that medieval England kept squirrels as pets and used their fur in European clothes. The fur frequently arrived via trade channels. In 1384, squirrel skins outnumbered other animal skin imports to England.

English norms did little to reduce the flood of squirrel goods, which may have spread leprosy in the region.

According to the World Health Organization, leprosy appears in over 120 countries annually, with over 200,000 new cases. Less than 1 case per 10,000 people are targeted to eliminate leprosy as a public health hazard worldwide.

Per World Health Assembly decision 44.9, this milestone was accomplished internationally in 2000 and in most countries by 2010.

Lowering new instances has been gradual worldwide and in WHO areas. Brazil, India, and Indonesia reported over 10,000 new cases in 2019.

Additionally, 13 nations, including Bangladesh, Ethiopia, and Nigeria, reported 1,000-10,000 additional cases. However, 45 nations had no instances, and 99 had fewer than 1,000.