"And the Lord spoke to Moses and Aaron, saying: When a man has on the skin of his body a swelling, a scab, or a bright spot, and it becomes on the skin of his body like a leprous sore, then he shall be brought to Aaron the priest ... The leprous person who has the disease shall wear torn clothes and let the hair of his head hang loose, and he shall cover his upper lip and cry out, Unclean, unclean" (Leviticus 13, on how to diagnose leprosy and what to do about it.)
Leprosy is mentioned dozens of times in the Bible. Though at least some cases could have been mange, the disfiguring, seemingly incurable disease was apparently common in the Levant during Old Testament times, more than 3,000 years ago. It also terrified Eurasia: the earliest-known case in India dates to 4,000 years ago, and the Atharva Veda, written in Sanskrit over 3,000 years ago, seems to describe this very condition.
Skeletons with apparently leprous malformations have been identified in Bronze Age Europe too, and Chinese literature written on bamboo in around 250 B.C.E. describes the suffering in detail.
For all these ancient accounts, we still don't know when the disease originated, let alone where. Comparative genomic analyses place its origin in East Africa or the Near East. Other theories suggest it began in southern Asia. Now a new international study, published Thursday in PLOS Pathogens, has looked into the genetics of the bacteria in medieval European skeletons, and discovered much more diversity in Europe than expected.
This leads the scientists to suspect a European or Eurasian origin for leprosy, because greater genetic diversity in an organism means it has had more time to evolve. This is true for bacteria, as well as for human populations, which show greater genetic diversity in Africa, where they all originated.
Also, in a startling aside, the scientists suggest that red squirrels – of all animals – were involved in at least part of leprosy's spread.
The squirrel, pet to some and pest to others, was fingered as a possible vector for Mycobacterium leprae bacteria in ancient England. No need to lay out squirrel traps: even though about 200,000 people a year still get leprosy today, it is treatable with antibiotics, and squirrels will not by choice go anywhere near you.
Don't kiss your squirrel on the lips
For their study, scientists from the Max Planck Institute, the University of Tübingen, EPFL Lausanne, the University of Zurich and the University of Cambridge sequenced 10 ancient genomes from Mycobacterium leprae extracted from 90 medieval bodies that, judging by the distortions left on the bones, had leprosy. All the bodies were European and dating between 400 C.E. to 1400.
It's really hard to extract usable DNA from ancient bones; that's why only 10 of the 90 bodies yielded suitable DNA. The 10 newly sequenced medieval leprosy bacteria genomes enabled the scientists to trace 1,500 years of the disease's history in Europe. The diversity they found startled them.
The earliest of the tested skeletons came from Great Chesterford, Essex, England, and dates to between 415-545 C.E. "This is the oldest M. leprae genome sequenced to date," write the scientists. And this is where the postulated squirrel connection comes in.
It turns out that ancient Chesterford Man and the latter-day Red Squirrel had the same strain of leprosy. So did three skeletons from Denmark.
One's mind leaps to bats possibly being the origin of Ebola virus, or birds being the source of SARS, and let's not even get into dogs and zoonotic malaises - but first of all, leprosy is a bacteria, not a virus. Secondly, if anybody infected anybody, we probably gave it to them.