But it is true, sort of.

One thing that many people are aware of is that mosquitoes are the deadliest animals.

That is of course because they transmit the deadly single cell parasite which causes malaria.

It is often said that malaria has killed half of all 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 and 1 million malaria related deaths.

This means malaria is still the most socio-economically devastating parasitic disease.

What has this to do with snails?

Well, similar to mosquitoes, snails also transmit a deadly parasite, a parasitic flatworm which is the second most deadly parasitic disease in the world.

This is however far less known 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 complex life cycles with morphological distinct generations and one or more intermediate hosts before they can infect their final host and these worms are no exception.

They begin their life as tiny larvae floating in the water.

Almost immediately after hatching they start actively looking for their intermediate host, freshwater 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 larvae quickly grow exponentially.

A process that started with a single larva has now produced thousands of offspring.

These so called Fog-tailed Sacarii 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 the Sacaria comes into contact with its host the larva penetrates the skin, sheds its 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 1-2 cm 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 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 warts 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 causes the problems are the eggs they produce.

A single female lays multiple hundred eggs per day for an average of 5 but sometimes as long as 20 years.

Only about 50% of these eggs penetrate the warts of the veins, make their way into the bladder or intestines and are released with a feces or urine to start the cycle again.

The rest remains embedded in the body, transported around by the bloodstream and 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, diarrhea and blood in stool or urine, the accumulation of fluid in the peritoneal cavity and hypertension of 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 anemia 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 infection with blood flukes can occur, the raw number of deaths, even if they are comparably 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 or fishing, or because of a lack of a reliable source of safe water for drinking, washing or bathing.

Children between age 10 and 15 are, due to their careless nature and their low level 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 northeastern Brazil and much of sub-Saharan Africa, the working ability of large portions of the population is severely reduced as a That's why, in the past few decades, health organizations 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 80 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 snare 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 flora and fauna.

Each control measure must therefore be applied and adapted specifically for each area to be affected, 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 1600s.

The southern, subtropical 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 fecal matter was stored for two weeks or more before using it as fertilizer.

Handpicking, snare pesticides and other chemicals were used to reduce the snare population and to kill the cercariae, and susceptible cows were replaced with horses as the animal of burden for agriculture, which were more resilient to infection.

To further control the snare population, wetlands were drained, river bottoms were dredged and ditches around rice fields were cemented, destroying much of the snare'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 10,000 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 the disease in Japan was largely eradicated with it, but a small population of them survived.

They are now living a life free from the parasites as well.