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. He stayed there for the next two years, and soon was able to observe the peculiar infestation of the rural houses with a large hematophagous insect of the genus "Triatoma", a kind of "assassin bug" or "kissing" bug ("barbeiro" or "barber" in Portuguese, so-called because it sucked the blood at night by biting the faces of its victims). He discovered that the intestines of these insects harbored flagellate protozoans, a new species of the genus "Trypanosoma", and was able to prove experimentally that it could be transmitted to marmoset monkeys that were bitten by the infected bug. Chagas named this new parasite "Trypanosoma cruzi" in honor of Oswaldo Cruz and later that year as "Schizotrypanum cruzi" and then once again as "Trypanosoma cruzi".