Climate Change and the European Water Dimension - Agri ...

VI.E. Climate change and waterborne and vector-borne
diseases
VI.E.1. Introduction
Climate can influence the emergence and transmission of infectious agents and the
specific mechanisms underlying the linkages between climate and infectious
diseases vary widely. Many diseases are clearly sensitive to changes in humidity,
temperature, precipitation and ultraviolet radiation intensity (Rose et al., 2001).
Among them are some of our planet’s greatest killers, such as malaria and cholera;
others (e.g. Lyme disease, hantavirus, Dengue fever), although less deadly, are still
dangerously debilitating. A first step is thus to define which characteristics make a
disease or pathogen “climate sensitive”. Climate change can influence the
epidemiology of infectious diseases by affecting the replication and movement of
disease agents and vectors or can influence transmission dynamics indirectly
through its effects on ecology or human behavior. As global temperatures continue to
rise, there are growing concerns that climate change may produce serious adverse
health effects. From 1889 to 1990, the global average temperature rose by 0.4-0.8°C
(Patz et al., 2001) and there is a nine out to ten chance that global average
temperatures will rise 4-7°C by 2100, with longer and hotter summers and milder
winters. However, to date, it is unclear to which extent climate change affect public
health through waterborne infectious diseases.
VI.E.2. Waterborne Diseases
Both water quality and quantity can be affected by ecological changes and
waterborne diseases (e.g. cholera, leptospirosis, schistosomiasis, giardiasis,
criptosporidiosis, human enteric viruses induced diseases, campylobacteriosis) are
or are suspected to be associated with weather-related components. Pathogen
concentration in surface waters may rise due to drought or increased precipitation
leading to enhanced runoff of pathogens with manure from the land. Coastal and
oceanic waters are known to harbor and transport pathogenic microorganisms and to
influence indirectly their distribution and disease patterns. El-Nino-Southern
Oscillation (ENSO) has been proposed to influence cholera outbreaks (Colwell,
1996) and has been associated with dynamics of the disease (Pascual et al., 2000).
ENSO has also been associated with levels of diarrheal disease in Peru’ (Checkley
et al., 2000). As a consequence of higher temperatures the geographic range of
many Vibrio spp. would be expected to increase with warming water. For a review of
the potential El Nino associated health effects (Kovats et al., 2003).
Heavy rainfall mainly causes storm water overflow thereby increasing pathogen
concentration in surface waters. Extreme precipitation also causes flooding of urban
and rural areas with wastewater contaminated by fecal pollution. Outbreaks are not
limited to countries with poor sanitation systems. In developed nations, heavy rains
overburden water treatment facilities and sewage systems: with spillovers of raw
sewage and animals waste from farms, high level of enteric pathogens are released
into local water supplies. More than half of the waterborne diseases outbreaks in the
US in the past 50 years have been preceded by heavy rainfall (Patz, 2004). With
climate predictions suggesting a greater intensity of storms and average
precipitation, waterborne diseases are likely to increase. Floodwaters and storm
waters can carry 1000 times the normal amount of disease-bearing microorganisms
(Ford et al., 1998) and have been associated to high incidence of gastrointestinal
disease. In a longitudinal cohort study, the rates of gastrointestinal illness during a
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