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