Poxviruses are the largest viruses
that infect vertebrates. This group include the human viruses – Variola (Small
Pox), Molluscum contagiosum, animal viruses, bird viruses and insect viruses.
Variola virus is the causative
agent of small pox. The vaccinia virus was used as the small pox vaccine.
Vaccinia virus is unique in that it is an artificial virus and does not occur
in nature as such. It is employed as a vector for the development of
recombinant vaccines. The genome can accomodate about 25,000 foreign bps, but
it is not suitable as a vector for human use due to its pathogenic effects.
