Catechism of the Catholic Church §419 — excerpt
"We therefore hold, with the Council of Trent, that original sin is transmitted with human nature, "by propagation, not by imitation" and that it is.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.