Abstract

Abstract

After a malaria-eradication program, no known autochthonous cases of malaria had occurred on Tobago. West Indies, from 1954 to 1966. In 1969, serum collected on filter-paper rectangles from 983 residents of the island was titrated for the presence of malaria antibody by the indirect hemagglutination test, with Plasmodium knowlesi as antigen. Serum was collected from three groups: 40 persons previously sampled in 1955; 27 persons that were infected with Plasmodium malariae in 1966; and 916 residents of the island selected from the general population. For the 40 persons resampled, antibody prevalence fell from 79% in 1955 to 10% in 1969. Of the 27 persons involved in the quartan-malaria outbreak in 1966, five (18.5%) had detectable antibody. In the sample of the general population, only 1% had demonstrable antibody and, with one exception, the positive reactions were in serum from older persons. These results indicate that hemagglutination antibodies become negligible in a general population within 15 years after eradication of malaria.