Development of antibodies to Plasmodium vivax as measured by two different serologic techniques.

Sera from individuals infected with Plasmodium vivax were tested for the presence of malarial antibodies using the indirect fluorescent antibody (IFA) and the indirect hemagglutination (IGA) tests. The primary infection resulted in the conversion of all sera to a positive response in the IFA test, whereas only 50% gave a positive IGA response. There was a direct relationship between the duration of the primary parasitemia and percentage giving positive IGA response. Relapse resulted in high level positive IFA and IGA responses.