View Full Version : Why leprosy died out: Europeans developed mutations

06-25-2013, 10:19 PM
Why leprosy died out: Disease did not evolve but Europeans developed mutations that made them resistant to it
Britons and other Europeans thought to have built up resistance to leprosy

Disease still infects 225,000 people every year across 91 countries

Scientists believe they are closer to solving the mystery of why leprosy suddenly declined in Europe 500 years ago.
Leprosy used to be one of the biggest killers across the continent with victims being cast out of towns and villages.

It is still found in 91 countries worldwide and infects 225,000 people each year but in Europe it suddenly declined in the sixteenth century.

Remains: Skeletons which contained the leprosy pathogen uncovered at the excavation of the St Mary Magdalen leper hospital in Winchester

One of the most popular theories as to why it declines was that the pathogen evolved and lost its virulence.
But scientists have now been able to discard the theory after discovering that the pathogen found today in the Middle East and other parts of the world is virtually identical that that of medieval Europe.

The discovery, made after genetic analysis of Mycobacterium leprae, the leprosy pathogen, recovered from Medieval bones in Britain, Sweden and Denmark, suggests that Europeans developed a natural resistance to the disease.

In a study published in the journal Science an international team of researchers concluded: ‘The sudden decline of leprosy in 16th century Europe was almost certainly not due to the medieval European strain of M. leprae losing virulence.

‘Extraneous factors such as other infectious diseases like plague or tuberculosis, changes in host immunity or improved social conditions may have accounted for its decline.’
In Europe sufferers were outcasts and had to ring bells to warn others of their approach.
In 1873 Norwegian physician Gerhard Hansen identified Mycobacterium leprae as the pathogen that caused the disease.
In the 1970s multi-drug therapies were developed as a cure.
Symptoms can take 20 years to appear.

Of the 3.3 million chemical letters found in the modern pathogen’s genome, just 20 were different to the Medieval version, said Dr Johannes Krause, a paleogeneticist at the University of Tuebingen in Germany.

‘If the explanation of the drop in leprosy cases isn't in the pathogen, then it must be in the host, that is, in us; so that's where we need to look, said Dr Stewart Cole, director of the Global Health Institute in Switzerland.

‘In certain conditions, victims could simply be pressured not to procreate. In addition, other studies have identified genetic causes that made most Europeans more resistant than the rest of the world population, which also lends credence to this hypothesis.’

He said it remains unclear if leprosy was taken to the Middle east by Europeans or the other way around but it is likely it spread during the Crusades.
‘We didn't have the data to determine the direction in which the epidemic spread,” said Dr Cole.

‘The pathogen could have been carried to Palestine during the Crusades. But the process could have operated in the opposite direction, as well.’

The leprosy pathogen was especially well preserved in the bones of this 25-year-old woman from Denmark