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10.2.4. Human Health
The IPCC Special Report on Regional Impacts of Climate Change (IPCC,
1998) acknowledges that climate will have an impact on vector-borne diseases.
The assessment in that report is limited to a qualitative analysis of the impacts.
The report identifies the scarcity of disease distribution maps and models as
a handicap to establishing current baseline limits. In the case of malaria,
however, a continental effort—Mapping Malaria Risk in Africa—is underway.
No such parallel efforts, however, are underway for other diseases in the African
continent that may be affected by climate change (e.g., arboviruses, trypanosomiasis,
schistosomiasis). No specific references are made to water- and food-borne and
epizootic/ epidemic diseases in Africa.
In recent years it has become clear that climate change will have direct and
indirect impacts on diseases that are endemic in Africa. Following the 1997-1998
El Niño event, malaria, Rift Valley fever, and cholera outbreaks were
recorded in many countries in east Africa (see Table 10-5
for a summary of disease outbreaks for the 1997-1999 period). The meningitis
belt in the drier parts of west and central Africa is expanding to the eastern
region of the continent. These factors are superimposed upon existing weak infrastructure,
land-use change, and drug resistance by pathogens such as Plasmodium falciparum
and Vibrio cholerae.
| Table 10-5: Summary of number of countries
in Africa reporting diseases/outbreaks from 1997 to July 1999.a Note that
outbreaks indicate above-normal disease prevalence. |
 |
| |
|
|
1999
|
| Disease |
1997
|
1998
|
(Jan-July)
|
|
| Malaria |
0
|
2
|
2
|
| Rift Valley fever |
0
|
4
|
1
|
| Yellow fever |
1
|
1
|
0
|
| Meningits |
3
|
2
|
|
| Plague |
2
|
1
|
2
|
| Cholera |
8
|
10
|
7
|
| Dengue |
0
|
0
|
0
|
|
10.2.4.1. Vector-Borne Diseases: Malaria
Although the principal causes of malaria epidemics in the African highlands
still are a subject of debate in the literature (Mouchet et al., 1998),
there is increasing evidence that climate change has a significant role (WHO,
1998). In a highland area of Rwanda, for example, malaria incidence increased
by 337% in 1987, and 80% of this variation could be explained by rainfall and
temperature (Loevinsohn, 1994). A similar association has been reported in Zimbabwe
(Freeman and Bradley, 1996). Other epidemics in east Africa have been associated
largely with El Niño. It can be expected that small changes in temperature
and precipitation will support malaria epidemics at current altitudinal and
latitudinal limits of transmission (Lindsay and Martens, 1998). Furthermore,
flooding could facilitate breeding of malaria vectors and consequently malaria
transmission in arid areas (Warsame et al., 1995). The Sahel region,
which has suffered from drought in the past 30 years, has experienced a reduction
in malaria transmission following the disappearance of suitable breeding habitats.
Yet, there are risks of epidemics if flooding occurs (Faye et al., 1995).
10.2.4.2. Cholera
Cholera is a water- and food-borne disease and has a complex mode of transmission.
Flood causes contamination of public water supplies, and drought encourages
unhygienic practices because of water shortage. The seventh pandemic currently
is active across Asia, Africa, and South America.
Colwell (1996) demonstrates the link between cholera and SST. Upwelling of
the sea as a result of increased SST increases the abundance of phytoplankton,
which in turn supports a large population of zooplankton—which serves as
a reservoir of cholera bacteria. Besides other epidemiological factors, the
effects of SST on the spread of cholera may be the most profound because they
affect large areas of the tropical seas and lakes. During the 1997-1998
El Niño, a rise in SST and excessive flooding (WHO, 1998a) provided two
conducive factors for cholera epidemics that were observed in Djibouti, Somalia,
Kenya, Tanzania, and Mozambique—all lying along the Indian Ocean.
Cholera epidemics also have been observed in areas surrounding the Great Lakes
in the Great Rift Valley region. Birmingham et al. (1997) found significant
association between bathing, drinking water from Lake Tanganyika, and the risk
of infection with cholera. Shapiro et al. (1999) have made a similar observation
along the shores of Lake Victoria. It is likely that warming in these African
lakes may cause conditions that increase the risk of cholera transmission. This
is an area that urgently requires research. According to WHO (1998a), Africa
accounted for 80% of the total reported number of cholera cases globally in
1997.
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