Connecting Global Priorities Biodiversity and Human Health

5. Waterborne and water-related
diseases
Long before the advent of modern medical care,
industrialized countries decreased their levels of waterrelated
disease through good water management.
Yet, even in these countries, outbreaks of waterborne
disease continue to occur, sometimes with lethal
consequences. In developing countries, water-related
disease blights the lives of the poor. Gro Harlem
Brundtland, former WHO Director-General, 2001.
Surface freshwaters are among the most altered
ecosystems on the planet and, coupled with
associated biodiversity loss, have been linked
to increased incidence of infectious diseases,
including waterborne illnesses (Carpenter et al.
2011; see also the chapter on infectious diseases
in this volume for a detailed discussion). Although
the global disease burden of many formerly
devastating waterborne illnesses (e.g. cholera,
typhoid fever) has declined considerably, others
continue to affect a significant proportion of the
global population, especially in the world’s lowestincome
regions, such as sub-Saharan Africa, where
the highest concentration of poverty occurs (Hotez
and Kamath 2009).
The presence of pathogenic (disease-causing)
microorganisms in freshwater can lead to the
transmission of waterborne diseases,¹⁰ many of
which cause diarrhoeal illness, a leading cause of
mortality in children under 5 years of age, and
among the most prevalent waterborne illnesses,
particularly in low- and middle-income countries
(Prüss-Ustün et al. 2014; WHO 2013; WHO and
UNICEF 2012; UNESCO 2009; Prüss-Üstün and
Corvalán 2006).¹¹ Unsafe drinking water itself
accounts for 88% of diarrhoeal disease worldwide
(including cholera, typhoid and dysentery) and
results in 1.5 million deaths each year, the majority
of them among young children (Prüss-Üstün et al.
2008; WHO 2003a).¹²
Factors that have been found to increase the
incidence of waterborne diseases include
urbanization and high population densities
of people, agriculture and industry (Patz et al.
2004). Habitat destruction or modification also
plays a major role. For example, dam-related
reservoir construction increases the prevalence
and intensity of human schistosomiasis in Africa
(e.g. N’Goran et al. 1997; Zakhary 1997) and
elsewhere (Myers and Patz 2009), as described in
Box 3. Climate change and the spread of aquatic
invasive species (see section 5.1) may facilitate
transmission of human pathogens (such as the
Asian tiger mosquito Aedes albopictus) and can
transmit viruses such as dengue, LaCrosse, West
Nile and chikungunya (Benedict and Levine 2007).
A strong relationship between the human
development index (HDI), access to drinking
water services and sanitation with mortality by
diarrhoea was found in some parts of the world,
particularly low-income countries. Almost half
of the population in these countries is at risk
of exposure to waterborne diseases, including
gastroenteric diseases such as dysentery,
giardiasis, hepatitis A, rotavirus, typhoid fever and
cholera. Less economically developed countries
such as Haiti, for example, had the lowest water
and sanitation coverage levels, coupled with the
lowest HDI values and highest child mortality
rates, in contrast to Chile, Costa Rica, Cuba and
Uruguay, among others, which had higher values
and coverage (PAHO 2012).
Human alteration of hydrological regimes has
often been motivated by concerns for human
health and well-being (Myers et al. 2013). While
altered waterways (e.g. dams, irrigation canals,
urban drainage systems) have indeed provided
¹⁰ The contamination of surface waters with fecal material from humans, livestock or wildlife has been identified as an
important (albeit not exclusive) pathway for the transmission of waterborne diseases (Prüss-Üstün and Corvalán 2006;
US EPA 2003; Ragosta 2010).
¹¹ See also http://www.who.int/mediacentre/factsheets/fs330/en/; http://www.cdc.gov/healthywater/wash_diseases.html
¹² Children under 5 years of age living in poor dwellings with inadequate access to health services are the most susceptible
to diarrhoeal disease and account for the overwhelming majority of all deaths attributed to these diseases (WHO 2004).
Relatively little is known about the pathogens that account for diarrhoeal disease themselves (Yongsi 2010).
56 Connecting Global Priorities: Biodiversity and Human Health