A seroepidemiological study was carried out on Orang Asli (Aborigines) children who lead a semi-nomadic life in the deep jungles of Ulu Kelantan, Malaysia. Out of a total of about 190 children below 14 years, 143 were studied. Blood was collected from finger pricks on standard "strip type" filter papers for indirect fluorescent antibody (IFA) tests with Plasmodium falciparum antigen. A positive reaction at 1:10 dilution in infants and young children was considered positive and the reasons are given. The P. falciparum antibody prevalence rate was 84.6% compared to 81.8% spleen and 43.4% parasite rates. Both P. Falciparum and P. vivax were present in children. The age-specific patterns of antibody, spleen and parasite rates were those of a hyperendemic community. There was a positive correlation between antibody and spleen rates up to the age of 9 years. In older children, the antibody rates increased while the spleen and the parasite rates dropped.
In 1973, 2610 sera were collected from adults living in 22 localities in four states in Peninsular Malaysia and tested by IFAT for Plasmodium falciparum antibodies. A larger number of thin films were examined. The attack phase of the Malaria Eradication Programme (MEP) in these areas was started between 1968 and 1973. The results showed that the highest prevalence rates and geometrical mean reciprocal titres (CMRT) were among adults from Kelantan where the antibody prevalence varied greatly among the adults and there was active transmission in at least three areas. The values were lowest for Kedah. The P. falciparum antibody prevalence rates were higher than the parasite rates as revealed in single thin film examinations but a number of the positive sera were reactive only at low titres. The low concentration probably indicated the residual antibody from cured cases or past infections and cross reactions to P. vivax and P. malariae infections. The strong reactions probably indicated current P. falciparum transmission as shown by positive thin films. The present study showed that the antibody profile of adults, as shown by IFAT, is of considerable value in assessing the malaria situation in a given area and that it would be useful as a malariometric tool in epidemiological studies to evaluate the progress of malaria eradication/control programmes.