“Whoever wishes to investigate medicine properly, should proceed thus: in the first place to consider the seasons of the year, and what effects each of them produces, for they are not all alike, but differ much from themselves in regard to their changes.” Hippocrates, in Airs, Waters, and Places.
The environment composing of various types of ecosystem services and functions (Figure 1) plays a major role in disease prevention. Some ecosystem services, such as purification of water, regulation of floods, natural hazard regulation, disease regulation, climate regulation and provision of aesthetic benefits remain unrecorded and yet have major impacts on human health. The World Health Organization recently estimated that 34% of all childhood illness in the world (compared to 24% of all age illness) and 36% of deaths in children under the age of 14 are due to modifiable environmental factors (1). Human population growth and environmental use through economic development and industrial activities have resulted in major improvements in both economic and health sectors. This success has however been at the expense of land degradation and transformation, loss in biodiversity, changes in biogeochemical cycles, pollution and most recently climate change. The effects of these environmental changes on human health as a result in ecosystem impairment are shown below (Figure 2) and are compounded by global warming and climate change.
Wood and Fibre
Figure 1: Ecosystem Services and functions. Source: Millennium Ecosystem Assessment 2005 (re-drawn).
Figure 2. Effects of escalating human pressure through ecosystem degradation on Human Health. Source: Millennium Ecosystem assessment 2005.
Climate is a key determinant of health. Climate constrains the range of infectious diseases, while weather affects the timing and intensity of outbreaks (2). A long-term warming trend is encouraging the geographic expansion of several important infections (3), while extreme weather events are spawning ’clusters’ of disease outbreaks and sparking a series of ’surprises’ (4). Impacts of climate change on health include both direct and indirect effects (Figure 3 (5)). The more direct impacts on health include those due to changes in exposure to weather extremes (heat waves, winter cold); increases in other extreme weather events (floods, cyclones, storm-surges, droughts); and increased production of certain air pollutants (e.g. Ozone) and aeroallergens (spores and moulds). The most severe effects of climate change on human health could be from those indirect mechanisms that would affect the transmission of many infectious diseases (especially water, food and vector-borne diseases) and decline in food productivity and access. In the longer term – and with knock-on effects of climate change to human movement, agriculture production, social and economic dimensions, that increase vulnerability – these indirect impacts are likely to have greater magnitude than the more direct (3).
Figure 3: Climate Change as a modulator of Human Health: Direct and indirect influences. Source: (5) (re-drawn).
According to the World Health Organization (6) over 30 new diseases have appeared since 1975. These diseases include AIDS, Ebola, Lyme disease, Legionnaires’ disease, toxic Escherichia coli, and a new Hantavirus. Of equal concern is the resurgence of old diseases, such as malaria and cholera. The emergence, resurgence and redistribution of new diseases cannot alone be attributed to climate change, but to a combination of changing ecological and climatic conditions as well as social changes. The ecological changes are more attributed to those infections involving two or more species such as mosquitoes, ticks, deer, birds, rodents and humans. In the latter category a change in one of the species changes the disease dynamics, the length of the lifecycle and in the long run the distribution of the diseases that it causes. It has been reported for instance that death in vultures mainly through poisoning has resulted in an increase in rodents that are very good reservoirs and host for a fair amount of vectors and vector-borne diseases. The knowledge of such ecological dependence is paramount to disease prevention. It is also known that through the "dilution and rescue effect" the number of biodiversity per se is important in disease prevention. Since the higher the biodiversity the smaller is the change of the vector feeding on the reservoir host and a high chance of feeding on non –important hosts and thus reduction on disease prevalence. Birds are well known to act as natural enemies to disease vectors; decline in bird population as we are witnessing will inevitably increase the infection prevalence in human (7).
In South Africa, from direct observation and surveillance it is noted that malaria in Limpopo Province has undergone a spatial change (Figure 4); whether or not this is a results of climate change is still under investigation. However models show that increases in temperature and change in rainfall patterns in southern Africa are already favouring the range expansion of some vectors-borne diseases such as malaria (7) and altering the range of tick-borne diseases (8). Furthermore a fifty-year analysis of temperature in Limpopo Province revealed an increase in the frequency of heat waves (9) that could potentially lead to an increase in deaths in the elderly and young children especially in those occupants of poor housing. And not to mention those with predisposed conditions such as heart conditions and others.
Figure 4. Malaria cases in Limpopo Province, 1998 and 2005
The effects of climate change on human health are an urgent issues that needs not only investing in long-term mitigation strategies but current adaptation plans and strategies. Societal adaptation to human health impacts from climate change will to a great extent be determined by the existence of accurate information and knowledge of diseases and the link between these and the climate. Modern early warning systems and sustained communication tools and strategies are but a foundation to protect our communities but could be more successful if indigenous knowledge and beliefs are incorporated. Traditional structures have immense knowledge and clues on the intensity of rain or storms and drought. Clues exist in the smell of the air, the type of flowers that bloom and this knowledge should be incorporated in the current scientific early warning systems. Building a common social responsibility platform (10) through the formation of village committees, women and youth social clubs with access to health and climate information can alert the rest of the communities on an impending climatic disaster.
Human health is strongly influenced by ecosystem services related to food production, water quality, water quantity, natural hazard regulation and they all depend on biological conservation. Changes in ecosystems influence the abundance of human pathogens such as malaria and cholera, rift valley fever, dengue, Lyme disease, tick-bite fever as well as the risk of emergence of new diseases. Some effects of climate change on health would be beneficial. For example, heavy rains as South Africa experienced in January 2011 could wash away mosquito eggs and larvae and lessen malaria incidences, and a further increase in temperature in currently hot regions might reduce the viability of disease-transmitting mosquito populations. Whereas we are investing resources and time on new medicines to reduce death from infectious diseases, our pursuit to ‘Health People” should also invest similar time and resources in producing ‘Healthy Environments” through sustained ecosystem management strategies, consistent surveillances of vectors, disease and their environmental determinants and the production of disease early warning systems in addressing some of the most pressing global diseases burden such as malaria.
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