Immune System Modelling and Simulation
202
With respect to other known diseases caused by viruses, the
natural history of HIV infection and the onset of AIDS shows
a singular time evolution that has particularly stimulated
mathematicians [130]: (i) the fi rst contact with the virus induces
a normal primary immune response, very similar to any other
infection, which lasts no more than a couple of months; (ii) this
acute phase is followed by a period of latency (from two to
eight years) during which the HIV plays ‘hide-and-seek’ with
the immune system; (iii) when the CD4 T-cell count drops to
about 20% of the normal value (around 10
3
cells per ml), there
is the onset of a highly immunodefi cient status. At this time,
the immune system becomes unable ...