Malaria eradication in Calabria, residual anopheles and transmission risk]

The paper is from a presentation at the meeting "La malaria in Calabria" (Cosenza, Italy, May 3, 1997) held to celebrate the half centenary of the antimalaria campaign (1947-1952) that eradicated the infection from the region. While Plasmodium falciparum had already disappeared in 1950, P. vivax persisted and the last autochtonous case was documented on the river Esaro in 1955. From the records of that time, it is clear that malaria eradication was achieved in the presence of important vector densities, as shown by larval surveys. Indoor DDT spraying, acting through the insecticide irritant effect, mainly avoided the house resting by the vector and forced the exposure of the mosquito to the outdoor environment where the lower mean temperatures eventually proved instrumental in destabilizing the parasite's life cycle. It is stressed that insecticide resistance never arised in the Anopheles vector populations of Calabria, in spite of at least ten years of continuous indoor spraying with an excellent overall coverage. This is expected in the absence of important selection pressures at the larval breeding sites and whenever the impact of the house spraying on the vector is due mainly to the insecticide irritant effect rather than to a direct imagocidal effect.