Relative increase in the prevalence of Plasmodium falciparum some years after the beginning of a house-spraying campaign in Netherlands New Guinea

1. 1) Following residual spraying in Netherlands New Guinea, it was observed that in areas where transmission could be stopped, P. falciparum was reduced most rapidly in the human-host reservoir, followed by P. vivax and P. malariae. This is in accordance with theory. 2. 2) In areas where the degree of transmission was only diminished, P. falciparum, after an initial fall, came to the fore again, and this species was responsible for a high proportion of the malaria cases which came for treatment. 3. 3) The explanation probably lies in the increased production of gametocytes which was most marked in P. falciparum infections, and may be due to the rapid loss of immunity of the human host to this species, as soon as the number of infections is diminished.