Study of the Mechanism of Relapse in Avian Malaria

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Abstract
In canaries carrying a latent infection of Plasmodium cathemerium or P. relictum, relapses may be conveniently and safely effected by subjecting them to an atmosphere containing O2 at 75 mm. Hg partial pressure. Kept in the low O2, birds recover in a few days. Suppressive drugs such as quinine, atabrine and plasmochin effect changes in the hosts in such a way as to make them relapse more severely than birds recovering spontaneously to the stage of latency; treatment clearly interferes with the development of resistance or immunity. By use of intraven. injns. of large numbers of parasitized cells it was found that low O2, epinephrine subcut., or glucose enterally apparently prevented phagocytosis of these injd. parasites by the reticulo-endothelial system of latent birds. Hence it appears that hyperglycemia, which results from low O2, administration of epinephrine or of glucose, may well play a determining role in effecting relapses in latent birds. Attempts to effect repeated relapses by low O2 lead rapidly to a condition in which relapses do not occur; in fact, a complete cure was produced in 2 of 10 birds thus studied. The acquired resistance is thought to be due to progressive immunization through the stimulus of the parasites developing in the period of the relapse. "Antibody" production apparently is not depressed as much as is phagocytic capacity in the expts. herein described.

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