MALARIA DIAGNOSIS - IDENTIFICATION OF AN ANTI-40-KDA POLYPEPTIDE ANTIBODY-RESPONSE ASSOCIATED WITH ACTIVE OR RECENT INFECTION AND STUDY OF THE IGG IGM RATIO OF ANTIBODIES TO BLOOD-STAGE PLASMODIUM-FALCIPARUM ANTIGENS/

The need for an alternative methodology to assess disease activity in the case of malaria led us to evaluate the usefulness of studying the humoral immune response to establish the diagnosis of past or recent m alaria. For this purpose, we analyzed sera from 439 individuals living in endemic areas of the Amazon region (Ariquemes, Rondonia). Individu als were classified according to the number and the date of past crise s. The enzyme-linked immunosorbent assay (ELISA) was performed to eval uate the IgG/IgM ratio so as to discriminate acute or recent malaria f rom past infections against crude and defined (SPF70) Plasmodium falci parum asexual blood-stage antigens. We also analyzed the humoral immun e response against components presented in crude P. falciparum antigen by the immunoblot technique. Use of the IgG/IgM ratio values did not allow us to differentiate acute from past infections. However, when we analyzed the humoral immune response to parasite components, we were capable of identifying a polypeptide with a molecular weight ranging u p to 40 kDa, which was recognized by all parasitized polyinfected indi viduals studied but not by individuals with negative thick blood smear s. In view of these data, we conclude that the 40-kDa polypeptide may represent a powerful tool in the diagnosis of acute malaria, mainly fo r screening blood donors in endemic areas.