It is generally recognized that strain differences exist in vivax malaria. These differences may be reflected in widely differing tendencies to relapse, and in widely differing relapse intervals. This study is concerned with the strain or strains of malaria endemic originally upon the malarious island, plus possibly other strains introduced with troops. This experience may be at variance with experiences with other strains of vivax malaria encountered elsewhere. With the strain or strains encountered, however, the following conclusions can be drawn:
1.In troops almost universally infected with vivax malaria, few or no individuals were cured of infection by suppressive atabrine therapy (0.4 gm. per week) administered for a period of six months during exposure on a malarious island.
2.Few or no cases of vivax malaria were cured by mass therapy with atabrine or with atabrine plus plasmochin after leaving the malarious island.
3.Initial attacks of malaria occurred as late as six months or more after discontinuing atabrine suppression or after mass therapy of any of the types employed.
4.Atabrine mass therapy did not alter appreciably the number of first relapses occurring after first observed attacks.
5.There was a definite tendency to relapse between the fifth and seventh week after the first observed attack, with a sharp peak in the sixth week.
6.No difference in course of disease was noted between the group which had had malaria attacks previously on the malarious island and had first observed attacks during the course of this study and the group which had not had malaria attacks on the malarious island and had actual primary attacks during the course of study. (The total time span from date of first exposure to infection to termination of study was one year.)
7.Plasmochin administered as a part of mass therapy apparently aided in lowering the peak rate of first observed attacks, and spread the experience over a longer time period without appreciably altering the final outcome as far as first observed attacks and first relapses are concerned. There may have been a slight tendency to lower the ratio of total relapses to first observed attacks, but this point is far from being clearly established and needs observation over a longer period of time.