 His published work on this method served as the basis of prevention of malaria all over the world, and was adopted by a service of the Ministry of Health in Brazil, which was established expressly for this purpose.In 1906, Chagas returned to Rio de Janeiro and joined the Oswaldo Cruz Institute, where he remained working for the rest of his life.In 1909, he was sent by the institute to the small city of Lassance, near the São Francisco River, to combat a malaria outbreak among the workers of a new railroad to the city of Belém in the Amazon.