The HIV infection is often divided into three phases: the acute phase, from the infection to 1 until 9 weeks after the infection, a phase in which the virus replicates and the number of CD4 lymphocytes is reduced; the asymptomatic phase, lasting from 9 weeks to often more than 10 years, in which the viral load remains stable and the CD4 count is not abnormally low; the AIDS stage, when the viral load is high, CD4 count is abnormally low and opportunistic diseases manifest.