Rivers globally carry deadly pathogens: study
A global study on pathogens in rivers finds that rivers harbour dangerous levels of diarrhoeal disease-causing pathogens
Diarrhoea is one of the leading killers of children under the age of five in developing countries. Diarrhoea is rampant in India, with diarrhoeal diseases being the most prevalent of all waterborne diseases in the country. Diarrhoea leads to the third highest proportion of child deaths in South Asia.
Cryptosporidiosis, leading cause of diarrhoea among children
A study titled ‘Cryptosporidium concentrations in rivers worldwide’ published in the journal Water Research informs that one of the important causes of diarrhoea is cryptosporidiosis, a parasitic infection which is a leading cause of diarrhoeal disease among children under the age of two in developing countries.
For example, cryptosporidium related deaths in children under two are estimated to be as high as 202,000 in both Sub-Saharan Africa and South Asia. Community based studies in India show that cryptosporidium alone contributes to 3.9 to 7.1 million diarrheal episodes and 58,000 to 146,000 deaths each year in children under two years of age.
What is cryptosporidiosis?
Cryptosporidiosis is a diarrhoeal disease caused by a parasite named cryptosporidium. The parasite completes its lifecycle in humans and animals. The disease spreads from person to person after the parasites are shed into the environment; and their oocysts are found in soil, food, water, or on surfaces that have been contaminated with faeces from infected humans or animals. Oocysts are essentially thick walled and sturdy cysts or spores released by the parasite that are highly infectious and can infect a person through water and food.
Infection often occurs through water, such as drinking or bathing in river water contaminated with faeces. Cryptosporidium oocysts can tolerate various environmental conditions and can survive in water and soil for many months. They can be transported long distances in the air and also flushed quickly into water sources because of their small size. The common symptoms of cryptosporidiosis include watery diarrhoea, stomach cramps and pain, dehydration, nausea, vomiting and fever.
Cryptosporidium in rivers
The study attempts to estimate the concentration of cryptosporidium parasite oocysts in rivers by using a global model that assesses and computes pathogen concentrations in rivers. The study takes into consideration human and animal sources of infection, the impact of factors such as the role of surface runoff in transport of oocysts from land to rivers, the impact of temperature and seasons on oocyst survival and spread, and the impact of soil, river sedimentation and river characteristics on the spread of infection.
The study finds that:
- Rivers are one of the important sources of infection. Oocysts reach rivers directly through point sources such as sewer pipes or indirectly through manure transported through surface runoff. Monthly average oocyst concentrations fall in the range of 10-6 to 10 2 oocysts L-1 (monthly load) in most places.
Critical regions with high concentrations mainly include India, China, Pakistan, Bangladesh, Nigeria, Algeria, South Africa, Mexico, Venezuela, coastal areas of Brazil and some countries in Western and Eastern Europe and the Middle East.- Human faeces are a dominant source of pollution, more so than animal faeces.
- High counts of oocysts are found in untreated sewage in very large cities in developing countries.
- Parts of India and South East Asia, West Africa, Brazil and parts of the west coast of South America show high seasonal variability in presence of oocysts. India, China, Mexico and Nigeria show more concentration of oocysts in January than in July.
The paper calls for the need to conduct more studies to gain insights into the transmission of cryptosporidium oocyst through rivers that can help in:
- Evaluating disease risk and gaining insights into risk factors
- Identifying sources and pathways of infection
- Devising effective control and management strategies to prevent further spread of infection among high risk communities.
Download a copy of the paper:
Cryptosporidium in rivers worldwide_Water Research_2019
SixDegreesNews note: The heading has been changed to reflect article content that highlights pathogens presence across global rivers
