Mousepox in inbred mice innately resistant or susceptible to lethal infection with ectromelia virus. III. Experimental transmission of infection and derivation of virus-free progeny from previously infected dams.

The incidence and duration of transmission of infection with ectromelia virus strain NIH-79 was tested in innately resistant (C57BL/6) and innately susceptible (BALB/c) inbred mice. Transmission by C57BL/6 index mice occurred through 3 weeks and by BALB/c index mice through 4 weeks, although the duration of infection in individual index mice was often shorter. Soiled caging that previously housed infected mice was inconsistently infectious. Transmission was high in cages where infected mice died and were cannibalized by cagemates, but was low to moderate in cages where there was no cannibalism. Infected mice that were bred 6 weeks after they were infected, delivered virus-free progeny and did not transmit infection to their non-immune breeding partners. Sentinel mice housed in the room with experimentally infected mice were seronegative for antibody to ectromelia virus and to other murine viruses. These results support the view that infection with NIH-79 virus is typically short-lived. They also indicate that breeding of recovered mice can save valuable colonies that have been exposed to ectromelia virus.