When we talk about diseases, related to the water cycle, they are generally divided into four different categories, waterborne, water washed, water-based, and water related vector diseases. Waterborne diseases, such as cholera and typhoid, occur when water is contaminated by an infective agent, as shown in this picture. What we mean by an infective agent, in this case, are micro organisms, including viruses, bacteria, and protozoa. A key aspect to this type of disease is that no development of the organism takes place within the water until the organism is ingested by a human. This provides the perfect conditions for the organism to multiply rapidly again, thus causing the illness.
These disease causing organisms are contained in the faeces of infected people, and so are strongly associated with poor sanitation. So to control against these diseases, the challenge is to improve sanitation, and improve the quality of water. Cholera, for example, a major public health problem in many countries, is caused by a rod shaped bacterium. There have been several epidemics that have been spread through many countries over the past 30 years. For example, in 2015, there were over 172,000 reported cases worldwide. Other examples of such waterborne diseases include polio, giardia, amoebic dysentery, and hepatitis A and E. Water washed diseases, on the hand, are directly related to poor sanitation, lack of personal hygiene, and a lack of water or washing facilities.
These diseases include trachoma, typhus, and ascariasis. Trachoma is an infectious disease caused by a bacterium that affects the eyes, leads to pain and breakdown of the outer surface or cornea, and eventual blindness if not treated. The bacteria can be spread by both direct and indirect contact with an infected person. In contrast, ascariasis is caused by a roundworm that infects people who eat food or drink water contaminated with ascaris eggs contained in faeces from infected people.
The worm has a fairly complicated life cycle inside the body, whereby the eggs hatch in the gut, and then burrow through the gut wall to migrate to the lungs, where they break into the alveoli and pass up the throat, where they’re then coughed up and swallowed. The larvae then passed through to the stomach for the second time and into the intestine, where they become adult worms. A third type of disease, that occurs in the water cycle, are water-based disease. These are caused by parasites, who enters a host who has contacts with water. Water is therefore an integral part of the life cycle of the parasite. These parasites include Guinea worm and bilhazia.
The host animal then perpetuates the cycle by contaminating water with urine and faeces. The control measures for preventing these types of diseases are to improve sanitation, reduce contact with infested water, and to protect the water supply. This slide shows the life cycle of schistosomiasis parasites that causes bilharzia, as an example. The parasite flatworm breaks through the skin and then heads through the blood to the lungs, where it develops further before heading to liver, where it feeds on the red blood cells. Eventually, it gets to the kidneys and the bladder, where it is excreted in urine and faeces.
Finally, there are water related infected diseases which require a vector, typically a mosquito, that carries or transmits a disease pathogen and undergoes part of its life cycle in water. Examples of water related infected diseases include dengue fever, yellow fever, Onchocerciasis which is river blindness, and malaria. In 2015, there were estimated 212 million cases of malaria and 429,000 deaths, causing massive amounts of health care costs and human suffering. Malaria is caused by a protozoa, which is carried by the female anophelene mosquito, which breeds in clean standing water. Dengue fever, meanwhile, is caused by a virus, which is caused by the aedes mosquito, which likes to breed in water storage containers.
Other mosquitoes, such as the culex mosquito, that carries disease that causes the swelling of the lymph system, known as elephantiasis, breed in dirty stagnant pools. Hence, in order to control these types of diseases, it is necessary to maintain a reliable water supply, improve water storage, carefully dispose of sullied water, and improve drainage. So having looked at the different diseases caused by poor sanitation and water supply, how can we best prevent infectious diseases? How can we reach Goal 6, and what is its impact on public health, the environment, and society?
This clearly requires an understanding of how such pathogens are spread from infected humans into the local environment from where they can then re-inject individuals, as has been shown in this video. In most cases, the key actions need to prevent the organism from infected individuals being able to spread directly or indirectly, which means the provision of effective sanitation systems. Equally, water sources need to be protected from the pollution of such organisms. And finally, hygiene education needs to be promoted such that people understand the importance of using sanitation facilities, accessing clean water, and responsible use and storage of water in the home. If all three areas are tackled at the same time, then the aims of Goal 6 can be realised.
We will be looking at each of these preventative measures in the next steps, by looking at different technologies that are available to tackle these objectives, and then considering some case studies in both rural settings and urban environments in Ireland, Africa, and India.