Evidence is emerging that many ecosystems on the African continent carry risks
of climate-driven threats to human health. Predisposing factors include geographic
location, socioeconomic status, and knowledge and attitude toward preventive
measures. For example, populations living above 1,500 m in the east African
highlands are at risk of epidemic malaria (Lindsay and Martens, 1998); those
living along the shores of the Indian Ocean and the Great Lakes are at a risk
of cholera infections when conditions for transmission are suitable (Birmingham
et al., 1997; Shapiro et al., 1999).
Elsewhere in the Sahel and other arid areas where there are humidity deficits,
populations are exposed to meningoccocal meningitis (Tikhomirov et al.,
1997) and, in flood-prone pastoral areas, RVF (Linthicum et al., 1990).
Vulnerability also can be increased by close habitation with animals that are
reservoirs of zoonotic diseases such RVF and plague.
The socioeconomic status of communities may determine whether safe drinking
water (piped water, rain-harvested water, and protected wells) is available
(Sabwa and Githeko, 1985). The quality of housing is important because simple
measures such as screening windows and doors will prevent the entry of disease
vectors into human dwellings.
Human factors such as knowledge and attitude and practice will influence health
care-seeking behavior of an individual (Karanja et al., 1999). For example,
individuals may choose to visit a local healer instead of a clinical facility,
and this could affect the progression and outcome of an infection.
At the institutional level, the fragile infrastructure is unable to cope with
the impacts of diseases. For example, flood areas often are inaccessible, and
delivery of medical intervention is hampered considerably. Furthermore, pathogens
such as those of malaria and cholera are resistant to commonly used medication.
In the case of malaria, more than 60% of cases are treated at home (Reubush
et al., 1995) with drugs that may not be effective (Karanja et al.,
1999), particularly in nonimmune populations. Misdiagnoses of fevers, especially
during epidemics of uncommon and unfamiliar diseases, leads to delayed treatment
and consequently high morbidity and mortality (CDC, 1998). In many cases, foreign
assistance is required, and this assistance may come too late. These factors
increase the vulnerability of affected populations.
Understanding how climate affects the transmission of these diseases will lead
to enhanced preparedness for early and effective interventions. Monitoring drug
sensitivity to commonly used anti-malaria drugs and antibiotics will prevent
the use of ineffective interventions. Communities that are exposed to water-borne
diseases such as cholera could reduce the risk of infections by using safe drinking
Several large-scale studies in Africa have demonstrated that insecticide-treated
fabrics (e.g., bed-nets and curtains) can significantly reduce the risk of malaria
infections (Lengeler, 1998). However, such interventions are not effective against
day-biting mosquitoes that are vectors of RVF.
Remote sensing is increasingly becoming an important tool in forecasting the
risks of transmission in malaria, RVF, and cholera. Hay et al. (1998)
have shown that the normalized difference vegetation index (NDVI) correlated
significantly with malaria presentation, with a lag period of 1 month. NDVI
is a function of climatic factors that are similar to those that affect malaria
transmission. Ability to use remote sensing to accurately detect parameters
such as ground moisture that determine flooding could provide local officials
with sufficient warning to allow for implementation of specific mosquito control
measures before a disease (RVF) outbreak (Linthicum et al., 1990, 1999).
In the case of cholera, it is now possible to utilize remote sensing and computer
processing to integrate ecological, epidemiological, and remotely sensed spatial
data for the purpose of developing predictive models of cholera outbreaks (Colwell,
10.2.4.11. Technology for Safe Drinking Water
Flooding, which can be exacerbated by climate change, often results in increased
contamination of drinking water. In other instances, drought and an increase
in surface water temperatures have been associated with transmission of cholera.
Although Cryptosporidium parvum is the more important water-borne pathogen in
developed countries, Vibrio cholerae is more pervasive in developing countries.
Giardia lumbria, a water-borne protozoa, has a universal distribution. These
pathogens pose serious threat to individuals whose immune systems are compromised;
furthermore, there are numerous records of resistance to antibiotics by cholera
bacteria (e.g., Weber et al., 1994). Therefore, it is essential that
populations that are vulnerable to water-borne diseases should enhance safe
drinking water technology.
Cryptosporidium parva oocytes are very resistant to chlorine and other drinking-water
disinfectants (Venczel et al., 1997). In addition, the cysts have a very
low sedimentation rate (Medema et al., 1998); consequently, boiling may
be the most appropriate method of disinfecting water where risks of infection
exist (Willocks et al., 1998). However, the use of submicron point-of-use
water filters may reduce the risk of water-borne cryptosporidiasis (Addis et
Several simple and inexpensive techniques have been found to be effective in
reducing the risk of infection with cholera from contaminated water. Huo et
al. (1996) found that a simple filtration procedure involving the use of
domestic sari material can reduce the number of cholera vibrio attached to plankton
in raw water from ponds and rivers commonly used for drinking water. In Bolivia,
the use of 5% calcium hypochlorite to disinfect water and subsequent storage
of treated water in a narrow-mouthed jar produced drinking water from nonpotable
sources that met WHO standards for microbiologic quality (Quick et al., 1996).
In many cases, boiling water is not possible because of scarcity of firewood
and charcoal, particularly in flooded conditions. These examples of low-cost
technologies should become widely available to populations that are likely to
be impacted by contaminated water supplies, especially following extreme flooding