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[ INTRO ]
Eradication is the holy grail of disease control.
It means we’ve eliminated all infections of a disease on Earth,
and we generally don’t need to worry about it anymore
And we’ve managed to do it twice, with smallpox
and a cattle disease called rinderpest.
Despite having only eradicated one human disease,
most scientists think we can do it again.
There are major efforts underway to eradicate polio and malaria,
although neither quite have the finish line in sight.
But there other targets that might be a lot closer.
They just don’t have the same PR.
Neglected tropical diseases, or NTDs,
are a group of 20 conditions defined by the World Health Organization.
It’s a wide-ranging list, but there are some common themes.
They occur mostly in tropical areas, and are caused or worsened
when folks don’t have access to clean water and sanitation.
They’re often carried by insects or other animals.
And the effects of the climate crisis have a tendency to make them worse.
But of all the common threads,
the clearest is that they affect those living in poverty.
The “neglected” in the name refers to the fact that these diseases
don’t receive nearly as much funding, attention, or research as many others.
And it’s not a coincidence that they also affect the poorest people on the planet.
Because when one of them moves into a higher-income nation, boom,
suddenly it’s less neglected.
If you add all the NTDs together, they kill around 200,000 people per year.
But their impact is much larger when you consider the
disability, stigma, and economic burdens they cause.
At least 10% of the world is infected with one of these,
including virtually everyone living below the global poverty line.
So if we stop a few, it would make a big difference in many people’s lives.
The good news is, we know how to prevent or treat almost all of the NTDs.
In 2012, many organizations committed
to eliminating or controlling 10 of them by 2020.
That was easier said than done, and it didn’t quite happen.
But that doesn’t mean no progress was made.
Let’s look at the stories of five of these diseases to see how we’re doing,
and why we haven’t been able to end them for good…
at least just yet.
Yaws is caused by a bacterium that’s related to syphilis.
It begins when a minor injury gets infected,
so places without sufficient access to hygiene are more at risk.
Roughly 80% of those with yaws are children.
The infection starts with a wart that turns into a painful ulcer.
Over time it can progress to a secondary stage and form lesions
on a person’s face, limbs, and genitals.
Lesions on the bottom of the feet can make it difficult to walk.
Hopefully you can already see how a disease doesn’t have to be life-threatening to be
a significant global burden.
Eventually, painful swelling and damage can affect the bones.
The good news is all that’s needed to cure it is one dose of the antibiotic azithromycin.
Which only costs about 17 cents per tablet.
Because of this, the World Health Organization
set a goal of eradicating yaws way back in the 1950s.
And back then they’d already managed to reduce its prevalence by 95%!
But they didn’t close the deal,
and things have bounced back since then thanks to a lack of monitoring.
The approach is to give azithromycin to everyone in an area,
to eliminate as many infections as possible.
But many remaining cases are in those who live nomadically,
so they’re hard to reach.
And they’re far from medical laboratories,
so health workers rely on rapid tests to find asymptomatic cases of yaws.
The problem is, these tests detect antibodies that stick around even after treatment –
meaning they can’t distinguish between current and old infections.
The WHO recommends active monitoring and testing to stay on top of the disease,
which is harder to do without an accurate test.
A new type of rapid test looks for two different antibodies and can confirm active infections,
but these are more expensive.
Despite these challenges, the WHO still aims to eradicate yaws by 2030.
You may or may not have heard of Hansen’s disease,
but you probably know its other name, leprosy.
There are some good reasons for the rebrand.
“Leprosy” is one of the most stigmatized diseases in history,
going all the way back to ancient texts like the Bible.
Though it’s probably worth mentioning that the word translated as “leprosy”
in English versions of the Bible doesn’t refer to the disease as we know it today.
For one thing, Hansen’s disease is much less contagious
than what was described in ancient times.
Like our last example, Hansen’s disease is also caused by a bacterium,
and is most likely spread through respiratory droplets.
But you need a lot of prolonged close contact with someone who is both infected and not
receiving treatment.
Transmission is tough to track, since the time
between infection and clinical symptoms is an average of 5 years, and even as long as
20.
The disease mainly affects a person’s skin, nerves, and mucus membranes.
This means skin discoloration, lesions, and small growths.
Nerve damage leads to muscle weakness and numbness.
If untreated, and the wrong nerves are affected, it can lead to blindness.
That numbness means people with Hansen’s disease are more prone to injuries or burns,
because they might not feel the initial pain quickly enough to react in time,
leading to damage over time.
This has led to the misconception that “leprosy” can cause fingers to fall off.
There is a cure available.
It’s a combination of drugs,
but the course of treatment can be as long as two years.
The good news is patients aren’t contagious after starting drugs,
and the World Health Organization provides the medication for free.
Sadly, even though the disease can be cured,
the injuries and disabilities it can cause are permanent.
Cases have fallen by around 1% per year since 2010 by some counts,
though others have it holding steady.
But there were still roughly 200,000 new cases in 2019.
The goal is to reduce this number by 70% when 2030 rolls around.
A big challenge is detecting and treating new cases as soon as possible through contact
tracing and access to quick diagnoses.
This means you can get people medication as soon as possible,
which stops the spread of the disease and hopefully avoids it causing permanent disabilities.
The COVID-19 pandemic slowed down this effort,
as it did so many other things.
It caused a 37% drop in case detection.
But as of 2021, the WHO is still aiming for that 2030 goal.
Schistosomiasis is caused by a variety of parasitic worms.
One part of their life cycle occurs in freshwater snails,
while the other part requires them to spend some time in humans.
The larvae can enter directly through skin in contact with infested water.
Once inside a person, the worms enter the blood vessels,
migrate to the intestines or bladder, and release their eggs.
This can cause immune reactions that damage many organs,
like the liver and kidneys.
The bladder-infecting variety can even cause bladder cancer
and increase the risk of becoming infected with or spreading HIV.
This means dealing with schistosomiasis is critical to addressing the AIDS epidemic.
Though schistosomiasis itself can’t be spread from person to person,
because the parasite’s life cycle needs a snail as the in-between step.
We need multiple strategies to fight this one.
First, we can treat it with a drug called praziquantel.
It can also be used preventively, and while it only costs a few dollars a person,
that’s more expensive than it sounds.
Around 105 million people received this treatment in 2019,
but over twice that number likely needed it, so we have a way to go.
For one thing, it can’t be given to preschool-aged children,
but a pediatric version is in the works and expected in 2024.
And the majority of infections are in children,
because they often spend time playing and swimming in water.
In addition to treatment, improved access to
clean water, sanitation, and hygiene education can prevent the disease,
and like, a whole lot of other issues in the bargain.
Finally, we can use pesticides that kill the snails.
Which is an important tool, though one with consequences for the ecosystem.
The pesticides can also kill fish,
which are often an important food source in affected areas.
The good news is that fish populations seem to bounce back after treatment,
and you can still eat the treated fish.
It’s just that blitzing an entire ecosystem with pesticides has some,
what you’d call off-target effects.
Total eradication of schistosomiasis isn’t on the horizon at the moment,
but the WHO does think we can eliminate transmission of the disease in 25 countries by 2030.
The climate crisis will be a factor, since where those snails live depends on temperature.
Some areas where the disease is prevalent may actually become too hot for the snails,
which would certainly be a silver lining.
But on the other hand, their range is expected to expand into regions
that are currently too cool,
which would spread the disease to places that don’t see it today.
Soil-transmitted helminth infections are the most prevalent neglected tropical disease,
infecting around 1.5 billion people.
That’s, um, nearly a quarter of all humans.
This is an umbrella term for a number of conditions caused by parasitic worms, including roundworms
and hookworms.
The worms spread via eggs in feces.
In areas where sanitation is poor, the eggs can end up in soil,
hence “soil-transmitted.”
They then infect people through unwashed food or contaminated water.
Hookworms can even infect people directly through the skin,
so walking barefoot or playing in the soil can put someone at risk.
Many people infected with just a few of these worms have no symptoms at all.
But as the old saying goes, more worms, more problems.
They can cause iron and other
nutrient deficiencies, general malaise, loss of appetite, and diarrhea.
They can also impair growth and development.
In extreme cases, the worms can obstruct intestines.
With these little worms living in over a billion people, we’re not going to eradicate them.
But we could stop the adverse effects from them.
The WHO six goals to that effect by 2030.
They include universal access to sanitation, and ending morbidity in children.
In 2019, 436 million children were given anti-worm medication,
but that’s less than half of those at risk.
And once again, we all know what happened in 2020…
Not only has COVID slowed things down,
but these infections can even make COVID-19 more severe.
So, that honestly seems a bit hopeless.
And at this point you might be wondering,
am I really just going to tell you that even though we really want to eradicate these diseases,
it’s just too hard to do in practice?
No!
Because we are on the verge of crossing one of the NTDs off the list for good,
and eradicating our second-ever human disease.
Dracunculiasis, also called Guinea Worm, is a parasite that can be up to a meter long…
and live inside you.
The larvae spread through contaminated water,
and after they mate inside of you,
the female worm grows for around a year.
There’s no vaccine or drug to prevent or get rid of the worm.
It needs to be ready to leave on its own.
And… skip ahead about 20 seconds if you don’t want to hear what happens next.
The worm eventually emerges from a painful blister, usually on the lower leg or foot.
Now, if you’ve got a painful blister on your foot
you’re probably going to find some water to soothe it in.
That’s exactly what the worm wants.
It releases thousands of larvae into the water and spreads the disease further.
Breaking the worm kills it, which can cause painful inflammation,
so it's best to pull it out alive.
Extraction involves wrapping it around a small stick to slowly and gently pull it out.
It’s a tedious and painful process that can take weeks.
In the 1980s, 3.5 million people were infected every year.
Amazingly, after decades of hard work, in 2020 just 27 cases were reported.
That’s not 27 thousand or anything, that’s just…
27!
How did we do it without drugs or a vaccine?
Organizations focused on access to
clean water, simple filtration systems to remove the crustaceans that carry the worm
larvae,
and chemicals to kill them.
The goal is to eradicate dracunculiasis before 2030,
though that’s after we missed our previous goal of 2020.
Even though cases are down to just dozens per year,
those tend to be in the most remote areas,
so in many ways the final few are the most difficult.
And recently, we discovered that dracunculiasis can also infect animals like dogs and cats.
This is a big new challenge for eradication,
since we now need to also watch animals closely for worms.
[Outro]
Each of the 20 Neglected Tropical Disease conditions
takes its own devastating toll on some of the most vulnerable people in the world.
You might have heard of some of the others,
like rabies, scabies, and sleeping sickness.
Even snake bites, despite not being a communicable disease, are technically included.
While different strategies are needed for each of these,
the common denominator is they all impact those already affected by poverty.
It’s a vicious cycle.
Poverty means a lack of access to things like healthcare and clean water,
which creates vulnerability to these diseases,
which can lead to loss of ability and productivity, and that worsens poverty.
So by investing in things that break this cycle,
like access to healthcare, clean water, and economic opportunities,
we can end some of these diseases for good
and help improve life for hundreds of millions of people.
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[ outro ]