Viruses typically cause disease shortly after infection, before the
immune system of their host can respond. There is no other example of a
viral pathogen which causes primary disease only after long and unpredictable
latent periods, only in the presence of neutralizing antibodies, and in
the virtual absence of gene expression, as HIV is said to do.
The number of HIV carriers in the U.S. has remained constant at one
million since 1985, when widespread antibody testing was introduced, yet
new viruses spread exponentially in a susceptible population.