IDO1 and infection: To evaluate the role of regulatory response mediated by IDO and HO-1 during hypervirulent strain infection and due to the low number of survivor mice, animals infected with strain 5186 were treated with both 1MT and ZnPp to block IDO and HO-1 since day 17 post-infection, and control non-treated and treated mice were euthanized at day 28 post-infection.