SPREAD OF DISEASE AND
CLIMATE CHANGE
Direct effects of global warming
Rising temperatures have two opposing direct effects
on mortality: higher temperatures in winter reduce deaths from cold;
higher temperatures in summer increase heat-related deaths. The
distribution of these changes obviously differs. Palutikof et al
calculate that in England and Wales for a 1°C temperature rise the
reduced deaths from cold outweigh the increased deaths from heat,
resulting in a reduction in annual average mortality of 7000.
The European heat wave of 2003 killed 22,000–35,000
people, based on normal mortality rates (Schär and Jendritzky, 2004).
It can be said with 90% confidence that past human influence on
climate was responsible for at least half the risk of the 2003 European
summer heat-wave (Stott et al 2004). The 2006 United States heat
wave has killed 139 humans in California as of 29 July 2006.
Spread of disease due to climate change
Global warming is expected to extend the favorable
zones for vectors conveying infectious disease such as malaria.
A warmer environment boosts the reproduction rate of mosquitoes
and the number of blood meals they take, prolongs their breeding
season, and shortens the maturation period for the microbes they
disperse. In poorer countries, this may simply lead to higher incidence
of such diseases.
In richer countries, where such diseases have
been eliminated or kept in check by vaccination, draining swamps
and using pesticides, the consequences may be felt more in economic
than health terms, if greater spending on preventative measures
is required.
One of the largest known outbreaks of Vibrio parahaemolyticus
gastroenteritis has been attributed to generally rising ocean temperature
where infected oysters were harvested in Prince William Sound, Alaska
in 2005. Before this, the northernmost reported risk of such infection
was in British Columbia, 1000 km to the south (McLaughlin JB, et
al.).
Global warming has been implicated in the recent
spread to the north Mediterranean region of bluetongue disease in
domesticated ruminants associated with mite bites (Purse, 2005).
Hantavirus infection, Crimean-Congo hemorrhagic fever, tularemia
and rabies increased in wide areas of Russia during 2004–2005. This
was associated with a population explosion of rodents and their
predators but may be partially blamed on breakdowns in governmental
vaccination and rodent control programs. Similarly, despite the
disappearance of malaria in most temperate regions, the indigenous
mosquitoes that transmitted it were never eliminated and remain
common in some areas. Thus, although temperature is important in
the transmission dynamics of malaria, many other factors are influential.
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