Tom,
It depends on how you define epidemic. An epidemic is generally a
large number of cases of an illness in a relatively short period of
time. Influenza is a good example of an epidemic virus.
Now, if you look at SIV, the situation is more complicated. In feral
African green monkeys in East Africa, 50% are actively infected with
SIV. However, SIVAGM causes no disease in this species. The virus is
essentially normal flora. The same situation can be seen in humans.
Epstein Barr virus infects >80% of the adult population, but causes no
detectable disease in most of those infected.
In addition, sooty mangabeys also carry an SIV which causes no disease
in sooty mangabeys. But inoculate a Rhesus macaque with SIVSM, and it
causes an AIDS-like illness.
It appears that in the species in which SIV is found naturally, it
causes little or no disease. Cross species transmission results in
disease, but this appears to rarely occur in nature.
Jay M.
