A global response to climate change / by Enrique H. Bucher

A global response to climate change by Dr Enrique H. Bucher Centre for Applied Zoology, University of Cordoba, Argentina )though scientists are still not certain, it is reasonable to suppose that an increase in the proportion of "green- house gases" in the atmosphere - carbon dioxide, methane and chloro- fluorocarbons - could lead to global warming. What is certain is that there has been a steady increase in carbon dioxide in the atmosphere over the past 40 years or so. The other gases may have increased to an even greater extent. If present trends continue, by the year 2100 there could be a rise in sea levels of between one and three metres and, by the middle of the next century, an increase of between 2.5 and 5.5 degrees Centigrade in the planet's overall temperature, accom- panied by a greater frequency of .g severe storms. 0:- the forest species would probably decline, a process hastened by a greater frequency of forest fires and loss of the soil moisture needed for forest regrowth. Urban forms of leish- maniasis, on the other hand, may spread into newly warmed-up areas towards the poles. Such climatic changes could affect j the epidemiological patterns of the ] tropical diseases in several ways. 1:0 Increases in rainfall and temperature, ~ for example, could expand the areas of ~ the world inhabited by malaria-canying ·~ Anopheles mosquitos towards the ~ poles. The disease would thus spread '----""'--------~-----' into areas where it has never existed or where it has been eradicated. On the other hand, such an effect might be counterbalanced by a "drying-out" and further desertification of tropicai regions, depriving large areas of the water conditions necessary for mos- quito survival. But on the whole, increasing temperatures could be expected to increase the reproduction rates both of the parasites and their vectors and hence augment transmis- sion of malaria. Forest habitat In the case of leishmaniasis, conti- nued exploitation of tropical forests could lead first to an increase in the proportion of forest forms of the disease, as the parasites take advan- tage of greater access to potential human victims. As they are gradually deprived of their forest habitat, though, W ORLD HEALTH. June- July-August 1990 The bloodsucking bug which transmits Chagas disease. Chagas disease, or American trypa- nosomiasis, is to a large extent isolated from the effects of climatic change, since the triatomine bugs that transmit it tend to live in poorly constructed rural houses, a habitat unlikely to be affected by global warming. But if the global warming and decreased rainfall lead to an expansion of semi-arid savannas, like the Gran Chaco of Argentina and Paraguay, these areas might be invaded by peasant farmers culturally adapted to semi-arid condi- tions. The result could be a replay of the sad cycle of overgrazing, forest destruction and poverty typical of such areas elsewhere in the world. Poor housing, a concomitant of this scenario, would ensure the spread of the triatomine bugs. As winter tem- peratures rose, there might also be a lengthening of the insects' summer reproduction and disease transmission period in temperate areas like Argen- tina and Chile. As vegetation changed, bugs with greater potential for trans- mitting the disease could in certain regions predominate over bugs with less or no disease-transmitting potential. In Africa, diminished rainfall and subsequent progressive desertification may restrict the areas of vegetation in which the tsetse fly vectors of sleeping sickness (African trypanosomiasis) live. Increased rainful would have the opposite effect. Large scale migration The effects of global climatic change on schistosomiasis, a typically water- related disease, would vary depending on local changes in water patterns. Where these become more irregular, the breeding habits of the water snail - the intermediate host of the schisto- some worms - could be disturbed. On the other hand, a growing water shortage could lead to large-scale human migrations and an increase in dam building for irrigation, two factors that could accelerate the spread of the disease into new areas. Another water-related disease, fila- riasis, might also be affected by global warming. The blackfly vectors of onchocerciasis (river blindness) and the mosquito vectors of lymphatic filariasis (elephantiasis) would repro- duce more quickly if there is a rise in the temperature and oxygen-content of water. Generally speaking, increased tem- peratures would raise the reproductive rates of disease vectors, adding to vector control difficulties. As a conse- quence, the shorter generation times for these vectors could favour the emergence of strains resistant to pes- ticides. So what can be done? Unless galloping population growth, fuel burn- 23 Schistosomiasis (or bilharziasis), onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) - these are among the diseases that could be encouraged by global warming. ing and deforestation can be halted in time, the available evidence strongly suggests that we will experience unpre- cedented changes in our environment. There is no time to waste. Research will have to be organized on a far more multi-disciplinary basis to explore the 24 multi-faceted, interconnected web of changes and their possible effects on tropical health. Planning in anticipa- tion of these changes will have to extend much further into the future, since short-term, stop-gap solutions will be quickly overtaken by the rapid pace of events. One topic of research should investi- gate how vectors and parasites are likely to respond to changing condi- tions. Systems should be set up as soon as possible to monitor changes in vector distribution and the incidence of disease so as to detect trends at their earliest stages. Adaptive strategies will have to be decided through coordi- nated national and international planning, in which tropical health con- cerns should be an integral part. A global solution In short, to deal with such a global problem, we need a global response. As far as health and disease are concerned, who is more suited to organizing such a response than a global body like WHO? • W ORLD HEALTH, June-Ju ly-August 1990