Australia’s Dengue Risk: Human Adaptation to Climate Change - Recent Advances and Issues in Environmental Science - page 134

Today, epidemic dengue is limited to regions of Queensland where Ae. aegypti
is extant, and the frequency of outbreaks has increased constantly over the past de-
cade [11]. Historically, epidemics of dengue were recorded in northern Queensland in
the late 1800s and in southeast Queensland in 1904-1905 [10]. Dengue epidemics in
1926, 1942, and 1943 all extended from Queensland south into NSW, stopping only
on the arrival of winter [12]. Derrick and Bicks [12] found that these dengue epidem-
ics ceased when the outside temperature reached a wet bulb isotherm of between 14
and15°C and suggested that a parameter of 14.2°C mean annual wet bulb isotherm
(T W ) best represented the limiting parameter for the 1926 epidemic.
The current drying of southeast Australia has placed this region's urban and ru-
ral communities on escalating water restrictions, with anthropogenic climate change
forecasts suggesting that this drying trend will continue [13]. To mitigate against this
regional drying effect and the stress it places on domestic water supply, state gov-
ernment rebate programs have been initiated to encourage the installation of large
(>3,000 l) domestic water tanks in towns and cities throughout this region. Data from
the Australian Bureau of Statistics [14] records that in 2006, 20.6% of all Australian
household dwellings had rainwater tanks.
Given the expansion of domestic rainwater tanks in southern Australia, and assum-
ing these domestic water tanks can provide oviposition sites, we ask this question: can
climate be assessed to determine the distributional limits of Ae. aegypti and dengue in
Australia? We fi rst use a genetic algorithm to develop ecological niche models for the
distribution of Ae. aegypti in Australia (using data points drawn from both historical
and contemporary collection sites) and evaluate the potential distributional limits of
Ae. aegypti in Australia under today's climate and in future projected climate change
scenarios. We map these limits in relation to published experimental and theoretical
projections of Ae. Aegypti's temperature limits and then compare all projections to
dengue transmission climate limits obtained from epidemiological studies of historical
dengue epidemics in Australian. We fi nd that human adaptation to climate change--
through the installation of large stable water storage tanks--may pose a more sub-
stantial risk to the Australian population than do the direct effects of climate change.
Additionally, we fi nd that using point occurrence data and environmental parameters
of climate and elevation to map the distribution of Ae. aegypti in Australia prove de-
ceptive and require interpretation as some Ae. aegypti collection sites exist outside our
ecological niche models and both theoretical cold temperature limits. This suggests
that Ae. Aegypti's domestic behavior--with a lifecycle based around human habita-
tion that includes blood-feeding and resting indoors as well as egg laying in artifi cial
containers around houses--plays an infl uencing role on distribution.
MATERIALS AND METHODS
Distribution of Aedes aegypti in Australia
Contemporary collection sites were regarded as those collected since 1980 because
most country towns had moved to reticulated water, steam powered trains had been
replaced by diesel, and the common railway station water-filled fire buckets were
removed [9, 17, 18]. Contemporary sites also include collections made between 1990