Combined diagnostic methods identify a remarkable proportion of asymptomatic Leishmania (Leishmania) chagasi carriers who present modulated cytokine profiles

Peripheral blood samples of 138 co-habitants from 25 families with recently diagnosed cases of visceral leishmaniasis in the Metropolitan Region of Belo Horizonte, Minas Gerais, Brazil, were analyzed by indirect fluorescent antibody test (IFAT), rK39 and Leishmania chagasi Enzyme Linked Immunosorbent Assay (ELISA), intradermal skin-test and Polymerase Chain Reaction (PCR) over a 12-month period. The cumulative positivity was significantly higher by PCR (29.7%) than by IFAT, rK39 ELISA, L. chagasi ELISA and intradermal skin-test (5.1%, 6.5%, 14.5% and 2.9%, respectively). In addition, the cytokine profile was measured in 16 of the 138 volunteers, of whom eight were asymptomatic carriers and eight were non-infected co-habitants. The innate immunity cells from asymptomatic carriers displayed, upon in vitro antigenic stimulation, a modulated increase in cytokine synthesis that was distinct from that observed in non-infected volunteers. This study suggests that the identification of a large proportion of asymptomatic carriers is facilitated when more than one diagnostic method is applied and that a mixed pattern of immune response is correlated with clinical status of asymptomatic individuals. These observations suggest also that asymptomatic infection by L. chagasi is a frequent event and that control programs could benefit by including this indicator in their interventions.