for some, to have all but disappeared into the history books.

But leprosy stills haunts many parts of the world and there’s an absurd amount that

we don’t know about the disease.

Leprosy has been around since at least 2000 B.C. but, after all this time, we still don’t

really know how the disease is transmitted.

We don’t know where it starts in the body.

Oh, and we can’t grow leprosy bacteria in a culture.

But... maybe we should start with what we do know.

My name is Cressida Madigan.

I'm an assistant professor at UC San Diego in the molecular biology section.

And I work on leprosy and other neurological infections to try to understand how these

infectious agents are damaging our nervous system during infection.

I love micro-bacteria which is the kind of bacteria that causes leprosy.

They're very unusual organisms.

And part of what makes leprosy bacteria, or mycobacterium leprae, so unusual is that it

is thought to only be able to replicate inside a living cell.

These bacteria can't be grown in the lab the way that we grow other bacteria.

We don't know why.

We don't know if maybe we're just missing a key component of the recipe that it needs

to grow.

Could also be that leprosy simply can not grow outside of an animal.

So, scientists like Dr. Madigan study leprosy inside living animals like mice, armadillos,

and zebrafish.

But this still makes the bacteria difficult to observe and run tests on, especially since

it occupies a unique part of the body - the nerves.

It’s the bacteria invading the nerves and the immune system’s response that eventually

causes the major symptoms of the disease.

So, while we aren’t really sure how the disease gets into the body or how it travels

to the nerve cells, we know it infects what are called Schwann cells, which produce the

protective myelin sheath that covers neuronal axons, helping to conduct electrical impulses

along the nerves.

So there's some evidence that when leprosy infects Schwann cells, it stops those cells

from being able to make myelin which is this sort of insulating wrapping that surrounds

the axons of our nerves.

Something about the infection causes the protective myelin to die.

And this is because the bacteria is destroying the small, but mighty mitochondria in the

nerve cells.

So mitochondria are sort of like the batteries within cells.

They produce the energy for the cell so that it can function.

So, as a cell, if you don't have mitochondria you will essentially die at some point, right?

Over time, the nerve axons also become damaged by the immune system’s response to the bacteria,

which is why people with leprosy can lose feeling in their skin.

But the immune system isn’t activated immediately and that’s because leprosy bacteria is notorious

for moving at a snail’s pace.

While other bacteria like e. Coli can replicate in as short of a time as 20 minutes and disseminate

quickly, leprosy bacteria replicates only once every two weeks or so.

So someone could be infected for years and not experience any symptoms because the bacteria

isn’t setting off any alarms.

This also makes the bacteria difficult to treat.

Many antibiotics work by targeting bacteria that are replicating.

So if you're a bacterium and you're not replicating, then you will be naturally resistant to several

classes of antibiotics.

To treat the disease, you’d have to take a cocktail of various antibiotics daily for

up to two years to make sure the drugs hit the bacteria at the exact moment it’s trying

to replicate.

And you would need to take multiple antibiotics at one time to ensure that the bacteria doesn’t

become resistant to the treatment.

Which is not ideal.

But the good news is, leprosy really isn’t that contagious compared to other diseases.

So part of the stigma of leprosy is that this disease is very contagious.

But that's actually not true.

In fact, you need to be around someone with leprosy for a long time to catch the disease.

It also helps that 95% of people are naturally immune to leprosy.

So in order to contract leprosy you have to be living with a family member who has the

disease who is infectious and you have to have close intimate contact with that person

for a period of years.

And while the symptoms are undesirable, leprosy doesn’t directly cause death.

In some patients, the symptoms take decades to manifest.

So… like we said earlier about the leprosy bacteria.

They're very unusual organisms.

The Byzantines knew about leprosy.

They knew that it was infectious.

And so to try to stop the spread of leprosy throughout the Byzantine Empire, the Byzantines

would assign leprosy patients to leprosaria which were like very posh leper colonies essentially

and the leprosarias were actually really nice places for patients to live.

They got free medical care, free food, housing and so life was so good within the leprosaria

that people started trying to fake the symptoms of leprosy in order to be admitted.

Oh, to be a leper in the Byzantine era… am I right?