Water-borne Disease

Water-borne Disease any disease that is transmitted or spread through contaminated water. Pathogenic microbes (bacteria and viruses) and some parasitic organisms are responsible for various diseases of man and other animals. Such infectious pathogens survive and spread in the environment using various strategies. Three main routes of spread are recognised - air, water and person-to-person contact. Air serves as the vehicle for entry of pathogens of the respiratory tract while water is the route for those of the gastro-intestinal system. Person-to-person contact causes spread of superficial infections such as skin diseases, and sexually transmitted diseases including AIDS. These mechanisms are not, however, mutually exclusive. Many infectious agents, some viruses for example, enter the body using the gut as the port of entry but soon leave the gut to reach target organs. Poliovirus is an example, which enters into the body with food and water, and then attacks the target organs such as the nerves to cause the characteristic paralysis associated with the disease.

Human gut is the route through which the bulk of the exogenous material that we use for survival is made available to the body. As such it is also the target surface to be exposed to a large variety of pathogens that are carried by food and water. Pathogenic organisms that are predominantly carried into the human intestine through water, and as a consequence also food since we rarely eat food without it being mixed with water during preparation or during eating, are called water-borne pathogens. Diseases caused by water-borne pathogens are water-borne diseases.

The most common category of water-borne diseases is represented by diarrhoea. There are two major types, watery diarrhoea and dysentery. cholera is the prototype of severe watery diarrhoea caused by the bacteria Vibrio cholerae. Certain other bacteria (bacilli) such as shigellae cause dysentery type of diarrhoea commonly called bacillary dysentery.

A group of salmonella bacteria that enter the gut through water may or may not cause diarrhoea at the onset of infection but their actual clinical manifestation is a type of fever called enteric fever, the prototype of which is typhoid fever.

Diarrhoea and other gastro-intestinal diseases are caused by pathogens that are water-borne or are carried through the medium of water. These diseases account for nearly a quarter of all illnesses in Bangladesh - about 12% by diarrhoea, and 10% by other gastro-intestinal illness including enteric fever. Thus water plays a major role in the overall disease profile of the country; air being the second most important vehicle accounting for 11% of all illnesses which includes pneumonia and other infections of the respiratory tract.

Diarrhoeal and other gastro-intestinal diseases follow a transmission pattern that is called faecal-oral transmission. The pathogen is released into the environment with faeces where it stays until finding re-entry through the oral route with contaminated food and water. The overall sanitation and personal hygiene standard of the community or the country thus in a large measure determines the extent of re-entry of the pathogen into the body. In a situation where disposal of faeces is unhygienic, surface water will be readily contaminated by the offending pathogens released with faeces leading to high level of faecal-oral transmission. Bacteria, unicellular intestinal parasites such as amoeba and Giardia, and the infectious units (eggs and cysts) of intestinal worms are transmitted through this route.

Bangladesh is a country with about 130 million people living in an area of 148,393 square kilometre making the country one with the highest population density in the world. Economically Bangladesh is in a less than an enviable position; it is generally ranked among the world’s 10 poorest countries. Over 80% of the population of Bangladesh live in the 64,000 villages of this agrarian country. Villages lack good sanitation and clean drinking water, and are beset with numerous other problems such as poor communication, lack of electricity, inadequate health services, etc. Defecation in open air is common all over Bangladesh. Overall conditions in rural Bangladesh are highly congenial for rapid transmission of enteric pathogens through the faecal-oral route, which is reflected in the disease profile of the country. In cities there is usually some sanitation system in place but the system suffers from many inadequacies and cannot be regarded as intrinsically much better. Although cities provide water to its dwellers, which is supposed to be safe, the poorly maintained sewerage system often contaminates the water during distribution, and overflow of sewage during rain and flooding is a regular phenomenon releasing heavy load of germ on the surface.

Clean water is a pre-requisite for reducing the spread of water-borne diseases. It is well recognised that the prevalence of water-borne diseases can be greatly reduced by provision of clean drinking water and safe disposal of faeces. Bangladesh is fortunate to be able to make available hand operated tube-well water to over 80% of the village population. The programme, which was undertaken couple of decades ago, has been acclaimed as a major success story of its sponsors, the UN agencies. Furthermore, motor-operated deep tube-wells are common in the villages that are used to irrigate paddy fields, which also provide clean drinking water. But clean water is not alone of sufficient impact on water-borne diseases, concomitant improvements in disposal of faeces is also essential. The government has thus undertaken programmes to promote construction and use of low cost sanitary latrines in the villages. These ventures have already achieved some success. [Zia Uddin Ahmed]

See also diarrhoeal diseases; disease profile; dysentery; food-borne disease; health profile.