With regard to retroviruses, especially FIV, which exhibits a marked cellular tropism towards CD4+ cells, a major contribution is expected in the presentation and manifestation of sporotrichosis (as occurs in cryptococcosis, where the alteration in the CD4 / CD8 ratio, fundamentally observed in cats with FIV, favors the dissemination of the fungal agent). The gene discussed is CD4; the disease is cryptococcosis.