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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 - PowerPoint PPT Presentation
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Hot Topic or Hot Air? Climate Change and Malaria Resurgence in East African Highlands
Hay et al. 2002
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, EthiopiaB – Kericho, KenyaC – Kabale, UgandaD – Gikonko, RwandaE – Muhanga, BurundiF – Amani, TanzaniaG – 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
Climate Change and the Global Malaria Recession
Gething et al. 2010
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%
and < 50%• Hyperendemic - PR ≥ 50%
and < 75%• Holoendemic – PR ≥ 75%
• Endemic malaria covered up to 58% of the globe
Pre-intervention endemicity (approximately 1900)
Global Malaria 2007
• Endemic malaria present 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
Contemporary endemicity for 2007 based on a recent global project to define the limits and intensity of current P. falciparum transmission
Change in Endemicity between 1900 and 2007
The range of malaria has been reduced (previous figures) but also its prevalence In most areas
experiencing stable malaria transmission, endemicity fell by one or more classes (67%)
Only a few locations had a rise in endemicity
Change in endemicity class between 1900 and 2007. Negative values denote a reduction in endemicity, positive values and increase
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