After eight years of a nation-wide campaign against malaria in Venezuela, malaria has been eradicated over a large area. The criterion of cessation of malaria endemicity established in 1950 by the National Malaria Society of the U.S.A. has been adopted. This area, where almost half (49 per cent) of the population of Venezuela lives, is believed to be the largest area, within the tropical zone, of malaria eradication following residual insecticide spraying.
In this area of North-central Venezuela, within the Costa-Cordillera and Llanos geographic regions of the country, the intensity of malaria was as high as in the most malarious zones of tropical America. The incriminated vectors have been A. darlingi, the most important of the Neotropic Region, and A. albimanus and A. albitarsis. Highly endemic and epidemic malaria were found in sections of the area.
DDT, applied at the rate of 2 gm. per sq. meter every six months, has been the insecticide used. At the beginning, however, 1 gm. every three months and later every four months was employed. In some districts, after malaria transmission ceased, other insecticides have been utilized: chlordane against flies and BHC and dieldrin against triatomids.
After exhaustive epidemiological investigations, which may be compared favorably with some used in the more developed countries of the temperate zone, the following facts were established. In one area of about 20,000 sq. km. no primary indigenous case of malaria has been discovered during the last three years. In another area of about 160,000 sq. km. no primary indigenous case of malaria was observed, during the last two years, with the exception of 2 cases near the border of the area, which seems to indicate that here also malaria endemicity has entirely ceased.
Of the incriminated vectors, A. darlingi has been eliminated by DDT residual spraying and is apparently eradicated from most of the territory under discussion. But the population density of the other two vectors, A. albitarsis and A. albimanus, has not been affected by the insecticide. This indicates that in a tropical zone in the presence of efficient vectors, malaria may be eradicated by DDT residual spraying without vector eradication.
With this experience it is expected that malaria eradication from most of Venezuela will be attained in the near future. Only two exceptions to this generalization are considered probable. The first involves two small areas representing only 3.4 per cent of the territory previously malarious, where out-of-doors transmission is taking place which will require additional measures. The second includes those districts inhabited by some nomadic and rather wild Indian tribes, most of them in Amazonas, Apure, Bolívar and Delta Amacuro, which may have to wait for their incorporation to Venezuelan society before they can be freed from malaria.