We are already seeing such viruses emerging.
Monkeypox, a previously rare and potentially fatal virus caught from rodents, is spreading through central Zaire.(31) Between 1981-1986 only 37 cases were known, but there have been at least 163 cases in one eastern province of Zaire alone since July 1995. For the first time, humans are transmitting the disease directly from one to the other.
An outbreak of hantavirus infection hit southern Argentina in December 1996, the first time the virus was transmitted from person to person.(32) Previously, the virus was spread by breathing in the aerosols from rodent excrement or urine.
New highly virulent strains of infectious bursal disease virus (IBDV) spread rapidly throughout most of the poultry industry in the Northern Hemisphere, and are now infecting Antarctic penguins, and are suspected of causing mass mortality.(33)
New strains of distemper and rabies viruses are spilling out from towns and villages to plague some of the world's rarest wild animals in Africa:(34) lions, panthers, wild dogs, giant otter.