Water-related diseases can be divided into four categories (105).
• Faecal-oral diseases can spread via water or food contaminated with faecal material. They include diseases transmitted by direct ingestion of the pathogen and those spread because of a lack of water for personal hygiene. Examples include cholera, typhoid, hepatitis A and diarrhoeal diseases.
• Certain diseases that spread from one person to another can be exacerbated by lack of water for personal hygiene. These include infections of the skin and eye (such as scabies and trachoma) and those carried by lice (such as epidemic typhus).
• Water-based diseases can be caused by pathogenic organisms that spend part of their life cycle in aquatic organisms and are often associated with standing water. In Europe, an example of such a disease would be cercarial dermatitis.
• Diseases can be spread by water-related insect vectors. These vectors breed in water and include mosquitos, which transmit malaria and dengue.
Waterborne outbreaks of disease are widespread throughout the WHO European Region. Since the early 1980s, organisms that had not previously been regarded as waterborne agents have been identified in outbreaks in the European Region: Campylobacter, Norwalk virus, Giardia and Cryptosporidium. In about 60% of the outbreaks, the causative agent is not identified (106).
Faecal-oral diseases are still a major public health problem in Europe. More than 12% of the population in the WHO European Region does not have access to safe drinking-water (83). The majority of these people live in countries in the eastern part of the Region, where acute diarrhoeal diseases are still a major cause of childhood sickness. Two thirds of infant deaths in Azerbaijan, Armenia, Belarus, Georgia and the Republic of Moldova are caused by acute respiratory infections and diarrhoeal diseases. Cholera outbreaks continue to be reported from Albania, the Russian Federation and Ukraine. Hepatitis A is endemic and has a high prevalence in central and eastern Europe and the countries of the former USSR.
The most significant waterborne disease associated with the public water supply in western Europe is cryptosporidiosis. Cryptosporidium is an intracellular parasite of the gastrointestinal and respiratory tracts of numerous animals. Cryptosporidium oocytes can survive several months in water at 4 °C and are among the most chlorine-resistant pathogens. When contamination occurs, it has the potential to infect very large numbers of people. This is illustrated by an outbreak in 1993 in Milwaukee, which affected more than 400 000 people (107). About 5000 cases of cryptosporidiosis are reported each year in the United Kingdom. A study in the United States has suggested a link between episodes of heavy rainfall and outbreaks of this disease, as the capacity of conventional filtration plants is often exceeded under such conditions (108).
Cercarial dermatitis is a water-based parasitic disease that is emerging in Europe (109). The intermediate hosts are snails of the genus Lymnaea, the abundance of which may increase in a warmer climate.
Controlling the disease is difficult, requiring strict maintenance of water bodies and the use of molluscicides.
The complex relationships between human health and problems of water quality, availability, sanitation and hygiene are extremely difficult to quantify. For example, there are multiple routes of faecal-oral transmission. Predicting the potential effects of climate change on water-related diseases therefore becomes even more difficult. Further, any attempt to do so must take into account water-management practices, the growth in demand for water and a number of other factors not related to climate.
Climate change could have a major impact on water resources and sanitation in situations in which water supply is effectively reduced. This could in turn reduce the water available for drinking and bathing and lower the efficiency of local sewage systems, leading to an increased concentration of pathogenic organisms in raw water supplies. In addition, water scarcity may necessitate using poorer-quality sources of fresh water, such as rivers, which are often contaminated. All these factors could result in an increased incidence of diarrhoeal diseases.
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