When the G7 met in Bavaria, Germany recently, one of the main items on their agenda was the threat posed by snails; freshwater snails. Surprising though it may sound, these tyrants are complicit in a disease that affects more than 249 million people worldwide, yet which few people can claim to have heard of.
Schistosomiasis is a debilitating, parasitic disease, whose symptoms include progressive damage to the bladder, ureters, genital tract and kidneys, progressive enlargement of the liver and spleen, intestinal damage, and portal hypertension. It is responsible for over 200,000 deaths per year and is second only to malaria in terms of economic impact.
So, why is it still such a big problem? Is it incredibly expensive or challenging to treat?
No. Treatment for schistosomiasis, with a single dose of the safe and effective drug Praziquantel, costs as little as 50 pence per person per year, plus it is progressively available free of charge through drug donation programmes. What’s more, given that a necessary part of the life cycle of the parasite is in the human body and that humans are the reservoirs of the African schistosomes, elimination of schistosomiasis is totally achievable.
It is welcome, then, that neglected tropical diseases (of which schistosomiasis presents the greatest burden and impact of the 17 identified by the WHO) featured on the agenda for the recent G7 meeting.
In the leader’s declaration, the G7 claimed:
"As part of our health system strengthening efforts we will continue to advocate accessible, affordable, quality and essential health services for all. We support community based response mechanisms to distribute therapies and otherwise prevent, control and ultimately eliminate these diseases. We will invest in the prevention and control of NTDs in order to achieve 2020 elimination goals."
We have commitment from seven of the worlds most advanced economies to tackling the diseases endemic in 149 countries and which affect around 1.4 billion people worldwide.
Praziquantel is the current most effective treatment for schistosomiasis. It is administered in a single oral dose, can be used safely during pregnancy and lactation, and with the aid of a dose pole can even be administered without the need to weigh patients. It was developed in a collaborative effort involving Merck in the late 1970s. Since 2007, Merck has supported the WHO in its effort to eliminate NTDs – specifically, it has pledged to donate 250 million doses of Praziquantel by 2016. They are committed for as long as it takes to achieve elimination.
The requirement of a human host in the life cycle of the schistosoma parasitic worms makes elimination possible. If the population at risk of infection are regularly treated early in life, the disease caused by the infection immediately disappears, improving health and development of an entire generation and creating the conditions for interruption of transmission of this scourge of humanity.
Given that the means to eliminate schistosomiasis already exist, priority should be given to making accessible the available safe, quality assured single dose treatments. This should work closely with disease control implementation programmes and in a constructive dialogue to assure continuous drug efficacy.
An acknowledgement from the G7 of the severity of neglected tropical diseases is progress, and a commitment to act against them is welcomed. But in the interest of maximising the benefits in the minimum possible time, the GSA believes the priority should be to increase the provision of Praziquantel and other preventive chemotherapy treatments, donated by the pharmaceutical industry, in the affected areas. Additionally we must empower and equip health ministries and communities in endemic regions to successfully implement large scale regular treatment programmes to reduce disease and prepare the conditions to interrupt of transmission. Coupled with education about sanitation and clean water, progress will be guaranteed. Many countries in Asia, Latin America and the Middle East have already demonstrated how schistosomiasis can be eliminated.
The G7 faces many challenges. But we should not underestimate the challenge posed by the fresh water snail. The GSA brings together all of the players that can help make this challenge a thing of the past. The time is now. Together we must, just say the word: GO!
Within the next decade we stand the chance of eliminating a disease which has existed for at least five hundred times that long. In 2013 it affected 8 times more people than HIV and 26 times more people than tuberculosis – and yet, you’ve probably never heard of it.
Schistosomiasis is the world’s foremost neglected tropical disease, whose symptoms include progressive damage to the bladder, ureters, and kidneys, progressive enlargement of the liver and spleen, intestinal damage, and hypertension. It is responsible for over 200,000 deaths per year and is second only to malaria in terms of economic impact.
But where does it come from and how has it evolved as a disease? Schistosomiasis probably developed around the time of the agricultural revolution, when communities settled in close proximity to a single water source. It has been suggested that schistosomiasis first evolved around the river Nile. Indeed, paleoparasitic techniques identified the schistosome circulating antigen in mummies of multiple Egyptian eras, up to 5,200 years old.
Prior to the discovery that the cause of schistosomiasis was a parasitic worm, preventative measures were taken to avoid contracting the disease - healthcare relied upon maintaining good sanitation and avoiding waters associated with the disease. In 1853, Theodore Bilharz identified the schistosome worm (hence the disease was called bilharzia – a name it carries by many to this day). Identification of the responsible parasite initiated a switch from preventative measure to scientific solutions.
The late nineteenth century is when schistosomiasis research became more focussed. It was motivated in large part by colonial ambitions of the European powers in northern Africa. Between 1893 and 1914 Great Britain, Italy, France and Germany sent commissions to investigate the disease.
In the early 1900s John Christopherson had noticed the absence of schistome eggs from the urine of patients treated with tartar emetic. He carried out a clinical trial on a group of 13 patients over the course of 2-3 weeks and found it to be remarkable effective although substantial side effects were recorded before therapeutic success.
In 1920, the treatment was given to 1634 patients suffering with schistosomiasis, and this number doubled the following year. By the 1930s, the freshwater snail was widely accepted to be the intermediate host, and henceforth a program of chemical intervention was used to kill the snails, though it is unclear how effective this was.
The first World Health Assembly was held in 1948, two months after the founding of the World Health Organisation. A committee was assembled to target schistosomiasis. At the time, consensus was that control would be best achieved through targeting the snail population, despite a lack of evidence evidence that this was effective in controlling the incidence of the disease in humans.
The difficulty of maintaining snail control measures, combined with increasing concern for the environment, paved the way for development of a new treatment for schistosomiasis. In 1979, a drug co-developed by Merck and Bayer, Praziquantel, was approved for human use. Large scale school or community based treatment with Praziquantel, now defined as preventive anthelminthic chemotherapy, was initiated in the early 1980s proving that morbidity due to schistosomiasis could be reversed even in spite of continuous transmission and exposure to reinfection.
Fast forward to 2013 and four countries (Iran, Lebanon, Morocco and Tunisia) have eliminated schistosomiasis, with a further seven (Egypt, Iraq, Jordan, Libya, Oman, Saudi Arabia and Syria) having now reached low schistosomiasis endemicity. Between 2006 and 2013 the proportion of people treated for schistosomiasis increased from 5-13%.
The GSA pursues the treatment and elimination targets as outlined by the WHO.. Though achievable, a few key challenges remain. Primarily, adequate supply of Praziquantel needs to be ensured. This has been aided by Merck who have increased their Praziquantel donation up to 250 million tablets by 2016. A clear window of opportunity therefore exists to maximise this drug donation programme and make as great an impact as possible over the next few years.
But Praziquantel doses alone will not tackle the problem. In order to achieve transmission control and disease elimination a multi-faceted strategy including education on disease control and prevention, WASH, and vector control is required.
Schistosomiasis has debilitated many hundreds of millions of people over its known 5000 year history. Now it’s time to resign it to the history books.
 Lewin, 1977; Reyman, Zimmerman & Lewin, 1977; Miller et al., 1992:555; Bouchet et al., 2002
 Reports on the results of the bilharzia mission in Egypt, 1915. Part I: transmission', J. R. Army med. Cps, 1915, 25: 1-55.
 Schistosomiasis progress report 2001–2011 and strategic plan 2012–2020