18 February 2014

Schistosomes: beware the water

Over 700 million people worldwide are at risk from parasitic worms called schistosomes (blood flukes), which are transmitted via swimming in contaminated water. The worms are a major problem and can cause a severe debilitating disease called schistosomiasis in their hosts, which, sadly, kills nearly 200 million people each year.

This is an adult male blood fluke. Note its highly developed mouth piece on the right, which is uses to 'clamp' onto the inside of blood vessels and anchor itself against the blood flow. Once secured, it feeds on the nutrients carried in the host's blood. The fold that you can see running through the centre of the worm is called the gynacophoric canal, in which the much smaller female worm lies in permanent copulation.

Due to the large distribution of the schistosomes and their prevalence in third world countries that have very little infrastructure, they are of huge concern to the World Health Organisation, who is trying to reduce the levels of infection by educating people in endemic areas of the dangers, improving sanitation and by ensuring that the drug praziquantel is readily available to as many patients as possible.

Unfortunately, praziquantel treatment is extremely unpleasant and results in a range of negative side effects in humans, including: dizziness, somnolence, seizures, arachnoiditis and diarrhoea. To make matters worse, the parasites themselves actually worsen these side effects and patients undergoing treatment can also suffer from urticaria, rashes and pruritus. This is due to the sheer volume of dead parasitic material that is released into the blood at any one time, which can also cause eosinophilia in leukocytes.


Schistosomes are waterborne and infect human hosts when they swim in contaminated water. As the host swims, they leave a trail of fatty acids from their skin in the water behind them. The parasite is attracted to these fatty acids (L-arginine inparticular) and then attaches itself to the host's skin. Once attached, schistosomes secrete acids and enzymes from acetabular glands and literally burn through the skin until they enter the bloodstream! The distinctive and unpleasant rash that results is often called 'swimmers itch'.

Due to the problems associated with praziquantel, many health agencies are beginning to acknowledge that the best way to combat schistosomiasis is to prevent human infection in the first place. The easiest way to do this is to treat infected waters with insecticides that kill water snails – another vector that is essential to the schistosome life cycle. Without water snails, schistosomes will be completely unable to infect humans and the problem of schistosomiasis is thereby solved!

Like most parasites, schistosomes have an extremely complicated life cycle where they morph through a range of different forms and, at different stages, live in more than one host.

One of the reasons schistosomes are such a major problem is because males and females live in permanent copulation with each other inside the human body so can literally release thousands of eggs in a very short space of time. Rather than the parasites themselves, it is actually these eggs that cause the symptoms of schistosomiasis – a chronic, severely debilitating disease that is usually fatal. The exact symptoms of schistosomiasis vary (depending on the species that has infected the host and where the worms prefer to take up residence), but the most common symptoms are given below:
  • Intestinal schistosomiasis is caused by the bowel-living species of blood flukes Schistoma mansoni and S. japonicum, and is associated with abdominal pain, diarrhoea and bloody faeces. Liver enlargement is frequently seen in advanced cases, which leads to gross abdominal swelling as fluid is forced into the host's peritoneal cavity as a side effect of abnormally high blood pressure
  • Urogenital schistosomiasis is caused by S. haematobium, which lives in the bladder, and is commonly characterised by haematuria (blood in the urine); lesioning and scarring of bladder tissue; ureter and kidney damage; genital lesions that lead to pain during sexual intercourse; and, in advanced cases, can lead to infertility and a variety of cancers

Liver enlargement is one of the most debilitating symptoms of schistosomiasis and is fatal in almost all cases. This is due to the large-scale, irreversible damage it causes to the host's body.

What makes schistosome eggs so problematic is the large spike that protrudes from their surface. This spike is designed to slice through the walls of blood vessels so the eggs can pass into their hosts urine or faeces (and thereby be passed back into water where they hatch and infect more snails), but can become caught in the host’s tissues upon occasional. Once an egg has become lodged, the host’s immune system identifies it as 'foreign material' and a type of leukocyte called a macrophage activates in response. Macrophages quickly form a granuloma around the egg, which is essentially just a tough wall of inert proteins that prevents the egg from interacting with the body’s tissues. Ordinarily, granulomas are beneficial and are eventually removed from the body, but this cannot happen with the trapped egg. Due to this long-term presence, the surrounding tissue begins to inflame and no longer functions correctly. This problem is exacerbated as an ever increasing amount of eggs build up in the organ and are themselves enclosed by granulomas! Eventually, the organ becomes so blocked and damaged that it is unable to function correctly - leading to the symptoms of schistosomiasis!

Scientists are currently working on a waterproof cream that mask the fatty acids on our skin when we swim (which will help prevent schistosomes from invading our body), but this research is still in its early stages and doesn't look likely to have a practical application anytime soon. For now, you should simply avoid swimming in any water where schistosomiasis is prevalent (no matter how inviting it may look). If you are travelling aboard, such as to Africa (where schistosomiasis is a particular problem), I strongly recommend that you consult your doctor and travel professionals to familiarise yourself with the risks of the area before you head out.

5 comments:

  1. Hi all,

    Anyone who was interested in reading this post might also like to listen to latest podcast by The Life Sciences Podcast. The podcast talks about helminths (the family of worms that schistosomes belong to) in general and discusses how the human immune system acts to fight off an infestation. The link can be accessed below:

    http://lifesciencespodcast.com/2014/03/03/episode-9-the-helminth-and-its-host-are-parasitic-worms-helpful-or-harmful/

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  2. your amazing thank you

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  3. Interesting, but factually incorrect in one respect: It is only the NON-human-specific species which cause this prominent, long-lived 'swimmer's itch', e.g. bird- or sheep-specific schistosomes. These can cause a nasty, red, papular rash for up to 21 days, like in your picture, as the schistosomulum is attacked and destroyed by your body's immune cells...
    However, the 'penetration rash' of those species which have co-evolved with us over time in Africa to elude our immune systems and to cause invasive disease (e.g. S. mansion, S. haematobium etc.) only lasts up to and hour max, if present at all.

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  4. Ejakulasi dini merupakan kesukaran seksual buat cowok yg ditandai bersama ketidakmampuan bersi teguh kedaluwarsa diwaktu bersambung intim. Ejakulasi yg terlampaui serta-merta nyaris tentu senantiasa menciptakan pasangan kecewa. kalau tak diatasi ganjalan ini mampu menghalangi keharmonisan hunian tangga.

    Kali ini kita bakal mengulas sekian banyak rahasia mengalahkan ejakulasi dini yg semesta dilakukan wong, alamat pemakaian remedi, gel, krim hingga dgn latihan-latihan pernafasan perut.

    hingga diwaktu ini tak ada remedi instan yg dapat mengobati ejakulasi dini. justru penyebab terjadinya ejakulasi dini serta belum didapati dengan cara tentu. beraneka ragam resep dan obat-obatan dibuat dan disebut-sebut dapat mengobati dan melebihi ejakulasi dini tapi terus tidak sedikit cowok yg kecewa.

    mengungguli Ejakulasi Dini bersama Cepat

    perihal ini yg menerbitkan ejakulasi dini jadi salah tunggal momok yg ditakuti seputar laki-laki, mampu dimaklumi dikarenakan factor ini tentang kesulitan keperkasaan dihadapan perempuan. sekian banyak jalma laki-laki lebih pilih kehilangan tugas daripada kehilangan kemampuan membebaskan pasangan.

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  5. please admin help me share this to those who still suffering of this ailment.
    . As a sign of gratitude for how my wife was saved from Schistosomiasis, i decided to reach out to those still suffering from this.
    My wife suffered Schistosomiasis in the year 2013 and it was really tough and heartbreaking for me because she was my all and the symptoms were terrible, she always complain of abdominal pain and swelling , and she always have skin itching. we tried various therapies prescribed by our neurologist but none could cure her. I searched for a cure and i saw a testimony by someone who was cured and so many other with similar body problem, and he left the contact of the doctor who had the cure to Schistosomiasis . I never imagined Schistosomiasis . has a natural cure not until i contacted him and he assured me my wife will be fine. I got the herbal medication he recommended and my wife used it and in one months time she was fully okay even up till this moment she is so full of life.Schistosomiasis has a cure and it is a herbal cure contact the doctor for more info on drwilliams098675@gmail.com on how to get the medication. Thanks admin for such an informative blog.

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