Hay et al. 2002
Hot Topic or Hot Air?
Climate Change and Malaria
Resurgence in East African
Highlands
Climate Change and Malaria
 Climate warming
 Increase in malaria outbreaks?
 Re-emergence of other vector born diseases?
 Mosquitoes (Genus: Anopheles) expanding
their range
 coinciding with warming temperatures and
increased precipitation?
A digital elevation model showing
reported malaria resurgence in high
altitude regions of East Africa:
A – Debre Zeit, Ethiopia
B – Kericho, Kenya
C – Kabale, Uganda
D – Gikonko, Rwanda
E – Muhanga, Burundi
F – Amani, Tanzania
G – Analaroa, Madagascar
Percentage change of incidence of
Plasmodium falciparum malaria
(1980 -2000)
Meteorological Changes
 No significant changes in climate in Kericho, Kabale,
Gikonko, Amani or Muhanga as reported by an ADF test
 Debre Zeit and Analaroa experienced significant
warming (1970 – 1995)
 Both lie at the edge of the East African highlands
 Greatest increase in malaria
 Other Factors?
Other Factors
 Drug resistance
 Vector control
 Health service provision
 Land use change
 Population growth and urbanization
Drug Resistance
 Focussing on Chloroquine resistance
 First appeared in East Africa in 1978
 Spread to all tropical African countries
 Still the major drug used in these areas
Examples of Drug Resistance
 Example 1: Kericho
(Kenya)
 Chloroquine resistance
likely cause of malaria
resurgence
 No change in climate,
environment,
population structure,
health care, or malaria
control measures
Examples of Drug Resistance
 Example 2: Gikonko
(Rwanda)
 Believed malaria
resurgence a result of
climate change
 Significance of
temperature trends not
tested
 Drug resistance was
dismissed as a possible
cause
Examples of Drug Resistance
 Example 3: Burundi
 Four measurements were
taken, between 1993 and
2001, to support climate
change as a mechanism
for malaria resurgence
 No statistical analysis
 Measurements from one
area
 Unmistakable evidence for
Chloroquine resistance in
the area
Vector Control
 Africa once had effective vector-control
programmes
 DDT application
 There has been a decrease in these vector
control services and these decreases
correspond with increases in malaria
resurgence
Examples of Vector Control
 Example 1: Debre Zeit
(Ethiopia)
 26 000 kg of DDT per annum
(1965 - 1979) down to 4000 kg
(1980 - 1993)
 Resurgence in malaria
 Example 2: Madagascar
 Huge epidemic in 1878 makes




malaria endemic to the country
1949 eradication programme –
very successful
Spraying terminated in 1960
followed by treatment centers
in 1979
Severe epidemic in 1988
1993 spraying re-introduced
Health Service Provision
 In East Africa:
 Population served by
hospital beds has
increased (1980-1990)
 Exception is Rwanda
 Overall there is a
decrease in health
services in these regions
 Occurring at the same time
as the malaria resurgence
The percentage change in population per hospital bed
using data for 1980 and for 1990
Land-use Change
 Measure level of
vegetation cover using
NDVI
 Positive correlation
between increased
vegetation and malaria
 Most sites showed an
increase in vegetation
cover (<8%)
 Occurring at the same
time as the malaria
resurgence
The percentage change in normalized difference
vegetation index (NDVI); the 1981-1985 average is
compared with the 1996-2000 average for each site
Population Growth and
Urbanization
 In East African
countries population
increase by 50% since
1980
 Population has
doubled in urban areas
to 26% in 2000
 44% by 2030
 Reduction of malaria
risk in urban
populations
The percentage change in the human population –
total (open bars) and urban (solid bars) – between
1980 and 2000
Conclusion
 Climate change could be playing a role in malaria
resurgence in the East African highlands
 The evidence for this is weak
 Five of seven sites experienced no significant change in
climate
 Other factors at play including:





increased drug resistance
decreased vector control
decreasing health services
increase in vegetation
growing population
 These factors track more closely with trends in
malaria resurgence than climate change alone
Gething et al. 2010
Climate Change and the
Global Malaria Recession
Climate Change Models and
Malaria
 Global malaria endemicity has declined in the
past 100 years
 Malaria control projects
 Affordable treatment
 Urbanization (Hay et al. 2002)
 Current belief is that global climate change
will increase the future global range and
intensity of malaria
 Based on model predictions
 Accuracy of models not been challenged
Recent Evidence
 Comparison map of global malaria prevalence
from 1900 to 2007
 Covers a period of undoubted climate change
 Observe changes in range
 Observe changes in endemicity
 Compared results to recent models which
predict the impact of future changes in climate
on the range or intensity of malaria
 Based on the current relationship between
temperature and vectors
Global Malaria 1900
• Map of parasite rates as
the proportion of
individuals with
Plasmodium species in
their peripheral blood (PR)
• Hypoendemic – PR < 10%
• Mesoendemic – PR ≥ 10%
Pre-intervention endemicity (approximately 1900)
and < 50%
• Hyperendemic - PR ≥ 50%
and < 75%
• Holoendemic – PR ≥ 75%
• Endemic malaria covered
up to 58% of the globe
Global Malaria 2007
• Endemic malaria present
•
•
•
Contemporary endemicity for 2007 based on a
recent global project to define the limits and
intensity of current P. falciparum transmission
•
•
in only 30% of the globe
In tropics mainly
Holoendemic malaria is
rare (patches in West
Africa)
North America, Europe
and Russsia essentially risk
free
South America is
hypoendemic or unstable
Most of central and
southeast Asia is
hypoendemic or unstable
Change in Endemicity between
1900 and 2007
 The range of malaria
has been reduced
(previous figures) but
also its prevalence
 In most areas
Change in endemicity class between 1900 and
2007. Negative values denote a reduction in
endemicity, positive values and increase
experiencing stable
malaria transmission,
endemicity fell by one or
more classes (67%)
 Only a few locations had
a rise in endemicity
Results of Comparison
 Comparison between current climate change
model predictions with the historical and
contemporary maps show:
 Increase in temperature does not necessarily
mean an increase in range or intensity of malaria
 Despite the known effects of temperature on the
range of the mosquito vector
 Non-climatic factors must be playing a greater
role in determining the prevalence of malaria
Climate-Biological Model
 Directly predict the effect of future climate
change on the spread of malaria and then
compare this to the effect that non-climatic
factors have on malaria
 Found that non-climatic factors acting to
reduce global malaria in the 20th century
reduced transmission rates more so than the
future increase in global temperature will
ever increase malaria transmission
Conclusion
 Using the comparison maps and climate-
biological models:
 In order for climate warming to increase malaria
transmission it must surpass the collective effects of
disease control programmes and urbanization which
act to reduce malaria transmission
 global temperature increases will not cause an
increase in malaria endemicity
 To ensure malaria endemicity continues to
decline, funding should be given to disease
control programmes to keep them current and
effective
Referenes
 Gething, P. W., D. L. Smith, A. P. Patil, A. J. Tatem, R. W.
Snow and S. I. Hay. 2010. Climate change and the global
malaria recession. Nature 465: 342–345
 Hay, S. I., D. J. Rogers, S. E. Randolph, D. I. Stern, J. Cox,
G. D. Shanks and R. W. Snow. 2002. Hot topic or hot air?
Climate change and malaria resurgence in East African
highlands. Trends in Parasitology 18: 530 – 534