Dynamics of transmission of Trypanosoma cruzi in a rural area of Argentina. IV. Serologic, parasitologic and electrocardiographic study of the human population.
A serologic and electrocardiographic study was carried out in people living in 18 households in La Invernada (LI), Departamento Figueroa, and in 20 houses in Amamá (A), Departamento Moreno, both in the province of Santiago del Estero, Argentina. Serological tests performed were indirect hemagglutination (IHAT) and indirect immunofluorescence antibody tests (IFAT). Complement fixation, direct agglutination and ELISA tests were also done for those sera, showing discordant results for either IHAT or IFAT. All people in LI and children up to 12 years old in A were studied by xenodiagnosis. Approximately 50% of the whole population was infected (50% in LI and 50.9% in A) and a similar prevalence rate was already recorded in children below 10 years. A moderate increase of infection rates was observed in successively older age groups, indicating that most of the people became infected in the first decade of life. Comparison of serological profiles of both populations suggests a protective effect of insecticidal control campaigns in those individuals born between 1961 and 1971. New surveys carried out in both populations 2 years later rendered a 4 times greater annual incidence rate in A as compared with LI (7.9% vs 1.8% respectively). No differences were found in the percentages of abnormal electrocardiograms among seropositive and seronegative individuals from both settlements. The prevalence of complete right bundle branch block (RBBB) was higher in seropositive than in seronegative people (4.8% vs 2.3%) but lower than those figures recorded for other parts of the country and the continent. This suggests that in spite of its high prevalence, Chagas' disease has low morbidity in both localities.