Seroepidemiological studies by indirect haemagglutination tests for malaria. Military recruit collections from Argentina, Brazil, Colombia, and the United States of America.

Seroepidemiological studies of 10 956 sera of military recruits from 4 countries in the Western Hemisphere suggest that the indirect haemagglutination test employing an antigen prepared from Plasmodium knowlesi adsorbed to human group O erythrocytes may be useful in epidemiological studies of malaria. Based on a titre of 1: 8, or higher, in a micro-titration of serum, the prevalence of serological reactors in the collection of sera from USA recruits was 0.9%, in the Argentina collection 4.6%, in the Brazil collection 20.8%, and in the Colombia collection 21.3%. In Brazil and Colombia the distribution of serological reactors correlated with the distribution of malaria as determined by active and passive surveillance. In Argentina, serological reactors were found in states where active and passive surveillance indicated that malaria had been eradicated years ago.