Anophelism without malaria: an ecological and epidemiological puzzle.

Since 1898, when it was established that malaria was transmitted by the Anopheles, the theory has had many sceptics and critics. One of the most serious objections was that Anopheles mosquitoes existed in regions which were not malarious, although they could have been, given the climatic and ecological conditions ('anophelism without malaria'). The history of this epidemiological problem passed through four different phases. In the first, it simply did not exist, because before Ross and Grassi's discoveries one can observe the presence of the Anopheles mosquitoes and the absence of malaria without considering it surprising. In the second phase it became a possible refutation of the mosquito theory of malaria transmission. In the third, after the definitive acceptance of this theory, anophelism without malaria was considered as a puzzle, a paradox, an enigma to be solved. Finally, in the fourth phase, after the discovery of the maculipennis subspecies complex, it became the aim of the antimalarial activities. The historical analysis of this epidemiological problem suggests many insights on the delicate and always changing malaria ecosystem.