Abstract: 1.1. The parasite-host combination of Plasmodium fallax in the turkey is ideally suited for chemotherapeutic studies. The course of parasitemia following blood inoculation is of a consistently reproducible nature. Exoerythrocytic stages are invariably produced from the blood stages at a specific time during the infection, with the ensuing death of the host. Spontaneous recovery is unknown in this host-parasite combination.2.2. A minimal length of time (approximately 13 days) appears to be required for the appearance of the exoerythrocytic segmenters in the tissues. This is true regardless of whether there has been a patent parasitemia.3.3. In the routine testing of the drugs at low dosage, no drug was capable of significantly decreasing the peak parasitemia as compared with that of the controls. In a supplementary test series, sulfadiazine was able to decrease the peak parasitemia significantly. However, the drug was being used near the toxic level for turkeys.4.4. When the drugs were used at higher dosages sulfadiazine had the greatest effect of delaying the peak parasitemia, while quinacrine cleared the blood of parasites faster than any other drug. Parasitemia was suppressed for the longest time under the isopentaquine regimen, and under the same regimen the mean length of time before death was increased.5.5. A greater immune response was elicited in the controls than in the birds treated with high dosages of drugs against subsequent reinvasion of the erythrocytes by the merozoites produced from the exoerythrocytic segmenters. Immunity appeared to be definitely lower when the antigen (the erythrocytic parasites) was removed by treatment.6.6. In the routine testing procedures, there was an indication that the 8-aminoquinolines (pamaquine, pentaquine, and isopentaquine) were able to prevent, or at least delay, formation of the exoerythrocytic stages.7.7. Special regimens of treatment with sulfadiazine and pyrimethathine showed that pyrimethamine was far more effective than sulfadiazine in inhibiting the formation of the exoerythrocytic stages.8.8. The prime requisite for curing blood-induced P. fallax infections in the turkey was found to be the killing of or the prevention of the formation of the exoerythrocytic stages.

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   |texte=   The effect of antimalarial drugs on the exoerythrocytic and erythrocytic stages of blood-induced infections of Plasmodium fallax in the Turkey
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