THE MALARIA PARASITE RATE AND INTERRUPTION OF TRANSMISSION.

Present methods for assessment of the attack phase of malaria eradication are inadequate, particularly lacking any objective parasitological criteria of success. On the basis of previous observations and development of theory, the authors first postulate that the effects of complete interruption of transmission should, ideally, include a regular progressive decrease of falciparum parasite rates in the ratios of 1: 0.4 in 6 months, 1: 0.16 in 12 months and 1: 0.026 in 24 months. Analysis of a series of programmes in which complete interruption of transmission is known to have been achieved shows that this postulate is valid, and that it is not materially upset by strain differences of parasites or by differences in the ages of the subjects examined. Vivax rates appear to fall at approximately the same rate; the rarity of data for vivax malaria makes firm conclusions unsure, but the postulate can be extended to rates which are predominantly due to falciparum infection but include some admixture of other species. A second, arbitrary, postulate is made that the slowest acceptable rate of fall in 12 months should be in a ratio not less than 1: 0.22, which would secure ultimate eradication in about one-third more time than the ideal fall; on this basis statistical standards are set up for assurance of confidence that the minimum rate is exceeded. Slower rates of fall are then related to reproduction rates causing them, the findings being illustrated graphically and by mathematical theory.