Climate change futures: health, ecological and economic dimensions

Health is the final common pathway of the natural systems we are part of, and climate instability is altering the
patterns of disease and the quality of our air, food and water. The following case studies integrate the multiple
dimensions of diseases whose range and prevalence are affected by climate. The studies are approached from the
perspective of a disease or condition (for example, malaria and asthma), a meteorological event (for example,
a heat wave and flood) or from the view of natural and managed Earth systems (agriculture, forests, marine
and water). The cases are organized according to background, the role of climate, health and ecological impacts,
economic dimensions, scenario projections and specific recommendations to reduce vulnerabilities.
Primary prevention for all the illnesses and events addressed include measures to stabilize the climate.
INFECTIOUS AND
RESPIRATORY DISEASES
extremes can work alone and in combination to influence
the prevalence and dynamics of a tropical vectorborne
disease, and, by extrapolation, how changes
may occur in temperate regions at the margins of
malaria’s current distribution.
THE ROLE OF CLIMATE
32 | INFECTIOUS AND RESPIRATORY DISEASES
CASE STUDIES
MALARIA
Kristie L. Ebi
Nathan Chan
Avaleigh Milne
Ulisses E. C. Confalonieri
BACKGROUND
Malaria is the most disabling vector-borne disease
globally and ranks number one in terms of morbidity,
mortality and lost productivity. Some 40% of the
world’s population is at risk of contracting malaria,
and roughly 75% of cases occur in Africa, with the
remainder occurring in Southeast Asia, the western
Pacific and the Americas (Snow et al. 2005). Up to
75% of cases occur in children, and over 3,000 children
die from malaria each day (WHO 2003).
Plasmodium falciparum is one of four types of malaria
and is responsible for the majority of deaths. While
advances in antimalarial drugs and insecticides in the
first half of the 20th century led to the optimistic view
that malaria could be eradicated, widespread drug and
pesticide resistance, and the subsequent failure of control
programs, proved this optimistic view wrong and the
world is currently experiencing an upsurge in malaria.
The three facets of this case study examine the impacts
of flooding on malaria in Mozambique, the indirect
impacts of drought on malaria distribution in northeast
Brazil, and the projected impacts of warming and
altered precipitation patterns affecting the potential
range of malaria in the highlands of Zimbabwe. These
studies serve as examples of how warming and weather
Climate constrains the range of malaria transmission while
floods (and sometimes droughts) provide the conditions for
large outbreaks. Warming, within the viable range of the
mosquito (too much heat kills them), boosts biting and
reproductive rates, prolongs breeding seasons and shortens
the maturation of microbes within mosquitoes.
For malaria transmission to occur, a mosquito must
take a blood meal from someone with malaria, incubate
the parasite, then bite an uninfected person and
inject the parasite. Warmer temperatures speed up the
maturation of the malarial parasites inside the mosquitoes.
At 20°C (68°F), for example, Plasmodium falciparum
malarial protozoa take 26 days to incubate;
but, at 25°C (77°F), the parasites develop in half the
time (McArthur 1972). Anopheline mosquitoes that
can transmit malaria live only several weeks. Thus
warmer temperatures permit parasites to mature in
time for the mosquito to pass it on to someone previously
uninfected.
Malaria is circulating among populations living at low
altitudes and increasingly in highland areas in Africa.
Heavy rains create mosquito breeding sites along
roadways and in receptacles (though flooding can
sometimes have the opposite effect, washing mosquito
eggs away). Droughts can lead to upsurges of malaria
via another mechanism: encouraging the migration of
human populations into (or out of) malarious areas.
Climate change is compounding other changes influencing
the distribution of malaria. Population migrations, deforestation,
drug and pesticide resistance also contribute and
public health infrastructure has deteriorated in many
countries (Githeko and Ndegwa 2001; Greenwood and
Mutabingwa 2002). But, as climate changes, warming
and weather extremes are likely to play expanding roles
in the spread of malaria (McMichael et al. 2002).