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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 water technologies.
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, 1996).
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 al., 1996).
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 events.
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