A Study of Relapse Plasmodium Berghei Infections Isolated from White Mice

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Abstract
Summary: The course of Plasmodium berghei isolated from mice with relapse was compared to the course of the stock infection in mice with induced latent P. berghei. In each of three experiments there were more patent infections and more deaths among mice after challenge with relapse P. berghei than there were after challenge with the stock infection, or than there were among unchallenged latent infection control mice. Statistical analysis of the data indicated that this difference in mortality was statistically significant and that there was no significant difference in the mortality of mice challenged with stock infection and latent infection control mice. Since none of the three relapse infections used were more lethal for normal mice than was the stock infection, it is indicated that an increase in virulence of P. berghei was not associated with relapse. It is suggested that biologic variation and the selective influence of the latent, or immune state resulted in the appearance of variants that could thrive in the immune host. It is suggested that such variants might be responsible for relapses and that the transfer of the variants to new immune hosts results in more patent infections and more deaths than did reinfections with stock P. berghei. It is also suggested that the observed trait of relapse P. berghei is relatively stable since one of the relapse infections was passed 24 times in normal mice before it was used in an experiment.