Application of the indirect fluorescent antibody method in a study of malaria endemicity in Mato Grosso, Brazil.

Four surveys of malaria endemicity were conducted in the Cuiabá Sector of Mato Grosso State, Brazil, at 6-month intervals during the period April 1970 to September 1971; during April 1970 a survey was also conducted in the Campo Grande Sector. Over 4,000 dual specimens--blood films for parasite diagnosis and filter paper blood spots for determination of fluorescent antibody (IFA) response--were collected from the general population, including school populations whenever possible. Parasitologic examinations yielded positivity rates ranging from 0.8 to 2.3%. In the Cuiabá Sector, sero-positives (larger than or equal to 1:20) ranged from 9.3 to 13.6%; in the survey in the Campo Grande Sector only 4.3% of the specimens were positive. There was an expected increase in IFA response with age in both the proportion of positives and mean maximum titers. In the Cuiabá surveys 75 to 91% of the maximum positive responses were to the Plasmodium falciparum antigen, while in Campo Grande only 46% of the maximum titers were for P. falciparum. The wide differences in malaria endemicity observed within the Cuiabá Secctor were attributed to differences in climate, geography, and degree of development of the several regions. A study of surveillance reports from 1966 through the survey dates revealed that the high rates of infection seen often resulted from detection activities in the larger cities and probably represented cases imported from endemic areas to the north and west. In order to interpret accurately the endemicity of malaria in an area and, thus, determine the necessity for introduction or continuation of control measures, thorough epidemiologic studies are necessary. The addition of a serologic method to normal surveillance can increase the accuracy of interpretation.