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Sante. 1997 Jul-Aug;7(4):263-9.

[Impact of changes in the environment on vector-transmitted diseases].

[Article in French]

Author information

1
ORSTOM, Paris, France.

Abstract

We have defined the relationship between infectious diseases and environmental conditions and considered the development of this relationship to its current situation, where human intervention is occurring more often and is becoming more aggressive. The increase in the transport of freight and passengers by air has allowed parasite vectors to spread quickly and easily over large distances. Every country can now be reached from any other country within a couple of days. Usually, foreign species are unable to establish themselves and to persist in the new environment; but the recent arrival of Aedes albopictus in Albania, Italy and the Americas is a cause for concern. Demographic pressure has increased the need for land and the exploitation of new areas leads to large changes in the vegetation. The classic example of this man-made damage is the destruction of tropical forest in Western Africa, but the destruction of herbaceous vegetation, such as papyrus, in East Africa, could also have serious epidemiological consequences. Streams and rivers have been managed for power production and irrigation. The use of dams, both large and small, and the culture of rice in paddy-fields produces large expanses of water which are suitable breeding grounds for mosquitoes and snails, the vectors of human diseases such as malaria and schistosomiasis in sub-Saharan Africa. They are, however, of lesser importance in Asia and the Americas. Urbanization imposes a set of very similar structures on a specific rural environment. The effect of these two factors on each other determines the pathologies associated with each town. The suburban area is a specific environment where both urban and rural diseases occur and are made worse by poor hygiene conditions (waste, sewage, etc.). However, not all man-made changes to the environment cause a deterioration in public health. Urban and agricultural development projects must consider these issues and should use medical and environmental studies to avoid causing epidemic-prone conditions or spreading endemic diseases. Currently, most studies are limited to listing the specific diseases in the target area and very few attempt to assess the possible consequences of changing the environment. Forecasting the consequences of changes in environmental management is of great importance, but it requires the development of multi-disciplinary teams in the field who must be involved in the planning and implementation of the projects.

PIP:

This work defines and distinguishes between intermediate hosts, vectors, and reservoirs and explains how their current world distribution is the result of evolutionary processes. Most intermediate hosts and vectors and the majority of reservoirs have well defined geographic distributions resulting from evolutionary processes that condition the disease they transmit or shelter. Within their areas of distribution, each species finds more or less favorable conditions for its development and multiplication and thus for disease transmission. All events that modify the climate or environment affect the epidemiology of the disease. Human intervention, spurred by demographic pressure and technological development, is becoming more frequent and more aggressive, changing vegetal covering, surface water, and urbanization patterns, and affecting the conditions for vectors, intermediate hosts, and reservoirs. The possibility of reaching any part of the globe by air within hours has also been an influence. Malaria, dengue, and other infectious conditions have been spread by water and air transport. It is currently impossible to estimate with certainty the prospects for implantation of imported species, but the example of the Aedes albopictus mosquito which has persisted in Albania for more than two decades after reaching the country by air is disquieting. Population growth has created demand for new lands, whose exploitation requires modification of the vegetation. Disappearance of the tropical forest is always obvious, but destruction of vegetation such as the papyrus of East Africa may also have serious epidemiologic consequences. Construction of large and small dams for energy production and irrigation and of rice paddies has a marked impact on vector populations and hence on such infectious diseases as malaria and schistosomiasis. Urbanization superimposes relatively uniform structures on specific rural environments. Periurban areas combine rural and urban pathologies, which are accentuated by poor sanitary conditions and uncontrolled land use. Not all modifications of the environment affect public health. But all development and urbanization projects should be accompanied by studies of the medical environment. Such studies are usually limited to inventories of preexisting diseases, with little anticipation of what might occur in the new conditions created.

PMID:
9410453
[Indexed for MEDLINE]
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