Horizontal transmission of recombinant vaccinia virus in strain 13 guinea pigs

At our research facility, guinea pigs subcutaneously inoculated with recombinant vaccinia viruses traditionally are isolated from other research animals because of the assumption that viral shedding and transmission may occur postvaccination. However, an extensive literature search failed to reveal any information supporting this assumption. The purpose of this study was to determine whether horizontal transmission of recombinant vaccinia virus vaccines occurs postinoculation in strain 13 guinea pigs and to what degree. We scheduled 12 strain 13 guinea pigs for three subcutaneous inoculations with 10(7) PFU recombinant vaccinia virus at 3- to 4-week intervals. An additional 36 unvaccinated or naïve strain 13 guinea pigs were either cohoused with these vaccinees, housed in cages directly below the vaccinated guinea pigs, or placed in cages located across, and downwind (relative to room airflow), from vaccinees. Pre- and postvaccination serum samples were analyzed for the presence of vaccinia-specific antibodies by enzyme-linked immunosorbent assay. All 36 of the unvaccinated guinea pigs tested negative for antibodies to the vaccinia virus at all time points. The absence of virus-specific antibodies in the nonvaccinated guinea pigs, whereas vaccinated animals seroconverted, suggests that horizontal transmission of recombinant vaccinia virus does not occur between strain 13 guinea pigs housed in the same study room, regardless of cage location.