An indirect hemagglutination (IHA) test for malaria was evaluated. Antigen was prepared from mature schizonts of Plasmodium knowlesi harvested from the blood of the rhesus monkey. The plasmodia were freed from red blood cells with distilled water and then disrupted in a French pressure cell. A 2% NaCl extract of the disrupted plasmodia was used to sensitize human, group O tanned erythrocytes.
This IHA test detected antibody titers of 1:16 or greater in 98% of slide-proved cases of malaria and in less than 1% of serum from persons without a history of malaria. The major problems in this technique included harvesting the correct stage of plasmodia for antigen, using the French pressure cell, and storing the labile disrupted preparation. Control of these variables has made possible a test that can detect antibody against a spectrum of plasmodia that infect primates, with a minimum expenditure of antigen.