Diarrhoea Pathogens Set to Flourish as Cities Expand
Published on by Ashantha Goonetilleke, Professor, Water/Environmental Engineering at Queensland University of Technology in Academic
Research shows that the problem is likely to become significantly worse in developing countries over the coming decades, as population growth and urbanization increase pressure on sanitation systems, helping the pathogens responsible for diarrhoea to flourish
Cryptosporidium is one of the most common parasites responsible for diarrhoea. People who are infected with the parasite excrete it in their faeces. In locations where sanitation is poor, the parasite enters water courses and continues to infect new people, via drinking water, irrigated crops or swimming and bathing in the water. Only a small number of Cryptosporidium need to be ingested to cause infection.
Climate change, population growth and urbanization will all affect the life cycle of this parasite, potentially increasing the chances of diarrhoea outbreaks. With that in mind, Lucie Vermeulen from Wageningen University in The Netherlands and her colleagues developed a model of the parasite life-cycle and explored how changes in sanitation, urbanization and population growth might affect parasite numbers in Bangladesh and India.
Currently there are large areas in both these countries with poor sanitation. "In Bangladesh, hanging toilets are quite common – toilet facilities hanging above a stream or lake – leading to direct inputs of faeces into surface waters," said Vermeulen. "And in India a large part of the population has no sanitary facility (they practice open defecation), and the faeces of these people can be transported with runoff to surface water."
Cryptosporidium concentrations in water are highest in urban areas because people live in cities in such close proximity. In their model, Vermeulen and colleagues estimated that 53% of total Cryptosporidium emissions in Bangladesh and 91% in India come from urban areas. Looking ahead, the problem is only likely to become worse. "Under our 'business as usual' scenario, Cryptosporidium emissions will increase by a factor of 2 for India and 2.9 for Bangladesh between 2010 and 2050," said Vermeulen, whose findings are published in Environmental Research Letters (ERL). Most likely these increases in parasite volume will translate into increases in diarrhoea outbreaks.
Exactly how much the parasites increase in reality will depend on whether sanitation provision manages to keep up with population growth and urbanization. Adequate sanitation systems and sewage treatment plants will help to keep parasite numbers down, but these systems need to be robust. "Sanitation systems should be 'climate proof' and not regularly overflow during heavy precipitation periods," said Vermeulen. Animal manure can also be a source of Cryptosporidium parasites, so careful use of animal manure on fields is also important. Meanwhile, measuring water quality and awarding 'blue flags' to safe natural swimming areas could help to cut infection rates.
Many other developing countries are likely to face similar problems to Bangladesh and India in the future and, as this model showed, the increase in parasites is worrying. But tackling the problem now, by improving sanitation and treating sewage, could save many lives.
Source: Environmental Research