Genetic causes involved in Leishmania chagasi infection in northeastern Brazil

A sample of 502 individuals from 94 families from Jacobina, State of Bahia, Brazil, was investigated to determine the causal mechanisms involved in Le ishmania chagasi (the causal agent of visceral leishmaniasis in the America n hemisphere) infection, as measured by the intradermic reaction to antigen s derived from this parasite, using complex segregation analyses. The resul ts showed evidence of a major genetic mechanism acting on infection, with a frequency of a recessive (or additive) susceptibility gene (q) of approxim ately 0.45. A small multifactorial component (H = 0.29) acting in conjuncti on with a major recessive gene (q = 0.37) is not ruled out as a concomitant causative factor.