Why Snails Kill 200 000 People Every Year

Why Snails Kill 200 000 People Every Year

Most people probably wouldn’t believe it
if they heard that snails kill around 200,000 people every year, making them the second
deadliest animal on the planet. But it is true – sort of. One thing that many people are aware of is
that Mosquitos are the deadliest animals. That is of course because they transmit the
deadly single celled parasite which causes Malaria. It is often said that Malaria has killed half
of all the people who have ever lived. And while this is probably no longer true
today it was most likely true for most of mankind’s history. Even today there are an estimated 200 million
new malaria cases every year and between 300.000 to 1.000.000 malaria related deaths. This means Malaria is still the most socioeconomically
devastating parasitic disease. What has that to do with snails? Well, similar to mosquitoes snails also transmit
a deadly parasite: A parasitic flatworm which causes Schistosomiasis, which is the second
most deadly parasitic disease in the world. This is however, far less know, which is probably
why you are here. So what exactly is Schistosomiasis? The disease is the result of an infection
with what is commonly called blood flukes. These are water bound parasites that you can
find in all kinds of freshwater habitats like lakes, swamps and rivers, rice fields, puddles
or roadside ditches. Many parasites need to go through a complex
lifecycles, with morphological distinct generations and one or more intermediate hosts before
they can infect their final hosts and these worms are no exception. They begin their life as tiny larvae free
floating in water. Almost immediately after hatching they start
actively looking for their intermediate host (fresh water snails) which they need to develop
further. Once they find one they penetrate the soft
body of the snail and begin to reproduce asexually. They do this multiple times during the 1-2
months inside the snails and as a result their numbers quickly grow exponentially. A process that started with a single larva
will end up producing thousands of offspring. These so called fork-tail cercariae then break
out of the snail into the water and start looking for their final host for which they
are now specifically adapted for. They have around 48 hours to do so before
they die. There are dozens of different species of blood
flukes, each specialized on a specific set of vertebrate hosts – birds, mammals and reptiles
all fall victim to these parasites – and of course humans. There are 5 species that are responsible for
the major forms of human Schistosomiasis. Once a cercaria comes into contact with its
host the larva penetrates the skin, sheds it tail and transforms into the juvenile form. It then starts to bore through the flesh until
it reaches the blood vessels. Here it will spend the next couple of weeks
migrating through the circulatory system via the heart into the liver at which point it
will have matured into an adult male or female worm around 1-2cm in length. Next the worms begin to join together in pairs
to reproduce (this time sexually). For that the more slender female is held permanently
in a groove in the front of the male’s body. The two worms usually remain jointed together
like this for life although it can happen that a female divorces a male to look for
a more genetically distinct mate. From the Liver the pair eventually migrates
to their final destination, either in the veins of the walls of the intestine or the
bladder – depending on the species. They will remain here for the rest of their
lives feeding on the red blood cells and the dissolved nutrients inside the blood, hence
the name blood flukes, while the female continuously produces eggs. Although all this sounds like something straight
out of a horror movie, the worms themselves are essentially harmless. What cause the problem are the eggs they produce. A single female lays multiple hundred eggs
per days for on average 5 but sometimes as long as 20 years. Only about 50% of these eggs penetrate the
walls of the veins, make their way into the bladder or intestines and are released with
the faeces or the urine to start the cycle again. The rest remains embedded in the body. Transported around by the blood stream they
will cause a host of long-term chronic problems in many organs. Which brings us to the disease itself: Schistosomiasis
can have a wide range of symptoms depending on the species of worm or the individual. Common symptoms are abdominal pain, diarrhoea,
and blood in stool or urine, the accumulation of fluid in the peritoneal cavity and hypertension
of the abdominal blood vessels, long-term kidney liver and bladder damage as well as
an increased risk of bladder cancer and HIV infection (the latter particularly in women). In children which are most commonly affected
by the disease it can also cause anaemia and impact the body development and the ability
to learn. In most cases these symptoms impair and disable
rather than kill but with over 78 countries affected and nearly 800 million people that
live in areas where infections with blood flukes can occur, the raw number of deaths
even if they are comparatively rare is obviously still extraordinarily high. It is estimated that currently over 230 million
people are infected and in need of medical treatment. The disease is only endemic to subtropical
and tropical regions and is mainly a rural problem. It affects mostly those who are unable to
avoid contact with water, either because of their profession (agriculture, fishing) or
because of a lack of a reliable source of safe water for drinking, washing and bathing. Children between age 10 and 15 are due to
their careless nature and low level of resistance most heavily infected. Impacted regions are South America, South
Asia, the Middle East, the Caribbean Islands and most notably Africa which has around 90%
of all known Schistosomiasis cases. The impact this disease can have not just
on the people but also on the economy of entire countries is serious. In areas that are most severely affected like
north-eastern Brazil and much of sub-Saharan Africa the working ability of large portions
of the population is severely reduced as a result of the weakness and lethargy causes
by the disease. That’s why, in the past few decades, health
organisations have begun to work relentlessly on limiting the impact of Schistosomiasis,
but the process is difficult and complex and while successful in some regions on a global
scale it was relatively unsuccessful thus far. That’s why the disease now ranks second
on the list of the 18 neglected tropical diseases issued by the world health organization. The biggest issue is the lack of an available
vaccine or any other reliable form of immunization. Merely the infection itself can be treated
through the use of drugs. Normally Praziquantel is used, which is effective
against all forms of Schistosomiasis, kills the parasites and even helps to reverse some
of the damage done by the infection. But while this treatment has helped to overcome
many of the long term problems of the disease and thereby reduced its mortality rate it
doesn’t prevent reinfections. That means that the ultimate goal – the
elimination of Schistosomiasis – is likely not reachable through medical means alone
– at least not at the moment. Instead it needs an integrated approach – So
a multi-component approach that targets the entire life cycle of the parasite: for instance:
preventive chemotherapy using praziquantel, improved detection and treatment of sick people;
improvement of sanitary facilities for safe and acceptable disposal of human excreta;
provision of safe drinking-water; reduction of contact with contaminated water; health
education; and snail control. But such an approach is of course very difficult
to realize and requires a long-term well-structured control program. What makes matters worse is that each region
is unique. The areas affected differ in part significantly
both socially, geographically, and economically and in terms of their flora and fauna. Each control measure must therefore be applied
and adapted specifically for each area to be effective, which explains why the elimination
of Schistosomiasis is such a challenge. Even in China where the disease has been actively
battled for more than 60 years now it still couldn’t be eradicated completely. But China’s example also demonstrates what
is possible through a long-term well-coordinated effort. Since their program was initiated in 1956
the number of detected cases of Schistosomiasis has dropped from more than 12 million to under
100,000 One country that could successfully eradicate
the disease is Japan. Here Schistosomiasis was endemic as far back
as the 16 hundreds. The southern, sub-tropical regions of the
country were most affected. After the cause of the disease was finally
identified in 1904, Japan as one of the first countries to do so, began to implement a series
of control measures to combat the disease. To kill the eggs, human faecal matter was
stored for 2 weeks or more before using as fertiliser. Handpicking, snail pesticides and other chemicals
where used to reduce the snail population and to kill the cercariae and susceptible
cows were replaced with horses as the animal of burden for agriculture, which were more
resistant to infection. To further control the snail population wetlands
were drained, river bottoms were dredged and ditches around the rice fields were cemented
destroying much of the snail’s habitats. All this was undertaken with government support
and performed by the affected communities. And it worked. In 1970 after 50 years of continuous effort
the number of infections had been reduced from around 10000 to a few hundred and no
new cases have been reported since 1977. In 1996 Schistosomiasis was then officially
declared eradicated. As a consequence of the program the freshwater
snail responsible for disease in Japan was largely eradicated with it. But a small population of them survived. They are now living a life free from the parasite
as well.


  1. Post
    Facts in Motion

    Because so many people commented about this under my last video I thought I make a video about it. Hope you like it.

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    Maintenance Renegade

    Considering how many perfectly harmless or even lovable species we've driven to extinction by accident or stupidity it blows my mind that we've never made a concentrated effort to completely exterminate the common mosquito or other such pests like these worms. As a species we're so good at killing. We need to apply ourselves better.

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    Oh baby give me one more chaaaance……

    The second deadliest animal sings as it mercilessly attacks a cucumber.🐌🥒

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    Tage Åkerström

    the production quality of these videos is truly astounding, every time you post im blown away. You deserve millions of subscribers and i love your channel. KEEP IT UP!

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    Ecboss C

    Thank you for this video! I had so many unanswered questions after watching the last video and seeing how many snails kill people

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    Tizona Amanthia

    This makes me wonder; do parasites and infectious "Creatures" deserve to live? is there any harm in their utter eradication? the snail is not at fault, so I wouldn't want to see them extirpated, But…are the blood worms beneficial to anything? are they prey of anything at any stage in their life? Leeches are gross parasites, but they're still part of the food web. same with mosquito. get rid of them, and you deprive other creatures of food sources. But what if there is nothing that would miss or be harmed by the removal of a parasite? That…means there's no real reason to not destroy it, live and let live…unless it's a useless parasite, right?

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    Kyle Stanley

    Shame people had to resort to habitat destruction to manage a disease as well as they had, but c'est la vie. At least the snails, the targeted species, survived all that. Tough fuckers, those mullusks :^)

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    Gotta love hearing German accents when it comes to learning something new. They're some of the smartest in the world.

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    again and again africa. all time there helping to health billions dollars/euro. Anyway this continent still stay a killzone: poverty, hunger, wars and illnes. when annihilate this shithole? even in poverty south america and south eastern asia dont have such epidemia and wars continuing for decades. Do they really not know about basic hygiene for so many years or are they masohist?

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    Why are these deaths attributed to the snails and mosquitoes instead of the parasites? What idiot came up with that idea.
    Also those parasites are a horror show.

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    So snails kill no people, rather worms kill 200k people. Also please dont glorify Japams systemic destruction of freshwater ecosystems, the disease was used as a scapegoat and the land was drained for profit.

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    the big takeaway from this is and frankly everything I've ever seen is that africa is unimaginably fucked and humans should absolutely not live there

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    One of the many reasons why worms are the most terrifying creatures on earth. Vermiphobia is 100% rational.

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    If malaria is the number one mortal disease by parasites and mosquitoes transmit the disease. Why don't we eradicate them just like they did those snails ?

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    Why not just kill the parasite through "natural" means?
    It must have a predator so let's introduce/increase the natural predator for the little fucker and run it out of existence while keeping and maintaining samples of it to increase their numbers should we need to reintroduce it to nature. Something akin to an engineered bacteriophage.

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    Livid Imp

    After watching this, I've decided to stop shitting in my drinking water!

    It was painful sitting on the opening on the jug anyway.

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    Stefan Oswald

    Besides the great, informative content and the spot-on presentation… WTF what is going on with the GCI on this channel?! The quality is absolutely amazing. Have not seen anything comparable anywhere else on Youtube. Fantastic!

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    Shiro Amada

    So paricites are the most and second most deadly thing. The masquito or snail doesnt have intent to kill and therefore isnt the "deadliest animal". I get english might not be your first language but click bait is still clickbait.

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    Ryan Stewart

    I do a lot of longer-term third world travel, and I always take de-worming pills of various types every 3-6 months in order to prevent long-term infection. These pills are extremely cheap in-country and if you don't have worms I don't think any have notable side-effects, but I don't think 99.9% of tourists are even aware of the danger.

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    Ry P

    Finally someone is talking about those silent, slow, sneaky serial killers.
    If the French and the German can agree on a thing, it must be true,
    boil the monsters and serve them with a delicious butter sauce!

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    First time in a while that I didn’t know anything about a topic discussed on a YT video. Thanks for the great explainer

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    Anis Optera

    Killing a disease by destroying habitats of the host species.
    That's the kind of method that could only be done in the 60s. Today there are riots if you drain marshes and concrete drainage canals and rivers.

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    Angelika Skoroszyn

    I've never understood why mosquitoes are considered the killers since malaria parasite are responsible for the deaths

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    I don't think you should blame the hosts of parasites like these as both the snails and mosquitoes suffer from the parasite. Technically with schistosomes we serve the same role in the life cycle of the parasite as mosquitoes serve in Malaria namely the primary host where sexual reproduction occurs. In Malaria we serve as the asexual reproductive host which means the parasites mass replicate inside the host in order to boost populations until they can readily infect their reproductive host. In summary we serve the same role as these poor snails do with Malaria.

    Eradicating the snails and wetlands is not the right solution as that comes at the cost of an entire ecosystem. Wetlands are highly important for controlling run off, flooding and supporting wildlife such as birds.

    Stop victim shaming wildlife >_<

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    Raymond Gonzalez

    Soooo I like traveling to visit family in the tropical lands of Mexico.. swimming and being near naked… should I be worried?? Haha

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    Amy Carter

    Well, some snails actually have some serious toxins in their excretions, but that's different from a free-roaming parasite that used the snail as an incubator. One of the snails I speak of that has some really harsh toxins in their excretions is the Blue Ridge snail, and despite the name, it's green in color, and has an average length of five inches (yeah it's a big snail). It has a very small amount of tetrodotoxin in its' excretions, about 1/1,200 that of the average bloat fish. It won't soak through the skin, but if ya have an open wound…yeah; just wear protective gloves when handling these snails. I actually have a few of these in my garden back home; they're good at maintaining plants and love Rafflesia.

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    Its very warming that some snails survived in Japan and are now parasite free. I would hate for them to be eradicated alongside the accursed parasite

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