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Scientists begin to unravel the secrets of leprosy

Leprosy has been striking dread in communities around the globe since ancient times, but fortunately for us, our defenses against the illness have evolved considerably over the centuries while the pathogen itself has not. That is the conclusion of a new study that compares the present-day alongside bacterium alongside the preserved genome of leprosy bacteria taken from Medieval-era grave sites and finds that both are remarkably alike.

Jesper Boldsen, a University of Southern Denmark biological anthropologist and study co-author, said that he and his colleagues exhumed the remains of several leprosy victims dating from the Middle Ages and extracted large amounts of well-preserved DNA from one skeleton. It subsequently made for a simple compare-and-contrast with present-day leprosy pathogens.

The leprosy bacterium, Mycobacterium leprae, had widespread notoriety back in biblical times, according to researchers. An ancient Egyptian papyrus written circa 1550 BCE records a description of leprosy, and the Bible’s earliest books include anecdotes of individuals exhibiting leprosy, as well as precepts for quarantining individuals who exhibit the symptoms. Communities throughout Europe suffered from leprosy outbreaks throughout the Middle Ages, with some of the worst concentrations of infections taking place in Scandinavia.

The disease remains deadly today, with around 250,000 new cases internationally each year and an estimated total of 10 million people living with it worldwide. Then, as now, the disease causes disfiguring sores and lesions to break out on its victims’ skin, followed frequently by severe disfigurations and loss of sensation and muscle strength.

That infection rate is just a small fraction of the infection rate of several centuries ago, however, following a precipitous decline in new infections starting in the 16th century. Also, doctors today have a suite of antibiotics that are able to treat most cases of it.

Leprosy’s history thus differs from the recent history of many other infectious diseases, whose pathogens tend to evolve very quickly. Epidemiologists are frequently frustrated in their attempts to develop new antibiotics fast enough to keep up with newly emerging pathogen strains, such as those responsible for staph, who exhibit immunities to older antibiotics and much more lethal potency than earlier generations of the same germs. It’s often a race between human innovation and bacterial mutation, and the bacteria frequently win.

Leprosy is an exception, however. Boldsen attributes this in part to communities since biblical times cordoning the infected off into leper colonies, away from the general population, and thereby slowing the disease’s spread. Additionally, as those individuals most susceptible died, they left behind survivors who possessed and passed down through their children varying degrees of immune resistance.

For the team of researchers, the discovery came at a cost. The DNA obtained from collected human bones contained less than 0.1 percent of the necessary DNA to reconstruct the disease. As a result, scientists were forced to create an extremely sensitive new method of separating the two kinds of DNA, before reconstituting the target genomes with unparalleled precision.

Among the most surprising findings: the medieval strain of Mycobacterium leprae discovered in the U.K. and Sweden is nearly identical to strains currently found in the Middle East.

According to the U.S. Centers for Disease Control and Prevention (CDC), in 2012 the number of new cases of leprosy detected worldwide remained well above 200,000. The CDC estimates that upwards of 249,007 people continue to suffer from the disease. In 2012 alone, 109 cases occurring in the United States were reported to CDC. Worldwide an estimated 1 to 2 million people are currently permanently disabled as a result of leprosy.