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Les mêmes causes ne produisent pas les mêmes effets : travaux hydrauliques, santé et développement Volume 3, issue 4, Décembre 1992

Author
Laboratoire d’Hydrologie ORSTOM, BP 5045 34032 Montpellier Cedex 01, France.
  • Page(s) : 227-34
  • Published in: 1992

Increased irrigation and other such developmental programmes always had an effect on the water-related parasitoses (malaria, filariosis, amœbiasis, schistosomiasis, ...) prevalent in the tropics. The rather blunt statement that increasing water availability always increases health problems, i.e. has the opposite effect or that planned by the engineers, must be qualified somewhat. To investigate this, we examined the case of malaria; being the major Third World disease, it is a suitable example. The number of malaria vectors increases substantially in irrigated paddy fields and man-made pools, yet disease does not increase in proportion to the mosquito (Anopheles sp.), but follows different rhythms linked to natural conditions and the epidemiological environment. Vectors such as arthropods, molluscs and rodents are highly affected by the often rapid environmental changes that occur in the tropics, especially in Africa (desertification and deforestation). Some species become scarce or disappear while others adapt to the new man-made environment and find favourable conditions in which to proliferate. As the vector’s ecological conditions change, so does the disease’s epidemiology; this may be due to the introduction of new diseases and vectors, intensifying exposure to existing pathogens and parasites or, on the other hand, to the elimination of diseases and vectors. In the case of malaria, increased vector density due to rice-growing may be associated with increased malaria transmission when the reproductive rate is low. But when malaria is at a stable level and transmission greatly exceeds that required to maintain the parasite, few changes will be observed. For any significant progress to be made in understanding the interrelationships between health, environment and increased water availability, we must adopt an interdisciplinary strategy. The approach we have adopted is to multiply case studies in order to include the widest possible range of actual epidemiological conditions. The aim is to predict the consequences of such development and control the negative effects.