Application of Malaria Serological Method for the Assessment of Epidemiological Features of a Hypoendemic Settlement in Amazon

Abstract

In the hypoendemic malarious area, classical malariometric measures such as spleen rate and parasite rate are not enough sensitive to detect latent malaria foci or to get the epidemiological feature in the population. A seroepidemiological study was carried out at a hypoendemic Amazonian colony Tome-Acu in Path, Brazil. In the area, malaria parasite was not detected in the surveyed inhabitants, nor splenomegary was reported at all. The malaria indirect fluorescent antibody test (IFAT) was applied to find the epidemiological picture of the area. In August, 1988, 148 Japanese settlers at Tome-Acu were comparatively studied with 162 migrant labourers and their families stayed in the same area. The frequency distribution curves of falciparum indirect fluorescent antibody titers showed bimodal pattern in a collection of sera from the migrants, however, the pattern was unimodal in the sera of settlers. The results suggested that the malaria was endemic among the migrants, but not among the Japanese settiers. IFAT positive rates by age group of the migrants showed a particular peak in the age range from 0 to 14 year. The peak like this was not shown in the distribution obtained from Japanese settlers. The findings were thought to support it that endemic malaria existed among the migrants but not among the settlers. IFAT positive rate of the migrants was decreased according to the elongation of their residence period in Tome-Avu. Interviews were performed from house to house to ask their past malaria histories, and answers were compared with the IFAT results respectively. The agreement rate of both questionnaire and serological test was 77.7 % in the settlers, while 56.8 % was obtained in the migrants. This survey presented the importance of application of IFAT in the hypoendemic area to obtain detailed epidemiological picture which was not obtained by classical malariometric measures. Application of IFAT together with the history questionnaire was useful to obtain the real state of the epidemic and inhabtants' knowledge on malaria.