Fetal Infection of the Baboon ( Papio cynocephalus ) with Vaccinia Virus

In utero infection of a fetus as a result of maternal involvement with one or another virus has been well documented (1–12). What has not been determined, however, is the spectrum of viral involvement and relationship to the period of gestation. Furthermore, specific localization of any given virus within the tissues of the fetus, following infection. is still relatively unknown. Studies to date have failed to relate maternal infection to the process of morphogenesis and embryogenesis in primates.

The purpose of this report is to provide information on the passage of vaccinia virus across the placenta at different stages of gestation. This virus was selected because of its size, known involvement in production of disease in primates, and well-studied biologic characteristics. Choice of the baboon (Papio cynocephalus) as the experimental model was based upon previous studies (13, 14) demonstrating its susceptibility to vaccinia virus as well as its close similarity to man in fetal morphogenesis and placental ultrastructure (15–17).

Materials and Methods. Animals. Nine pregnant baboons were divided into three groups depending upon their stage of pregnancy; first, second, or third trimester. No attempt was made, at this time, to define the precise stages of gestation as we were primarily concerned with attempts to determine localization of virus in the placenta and fetal tissues. The placenta and fetus were removed by cesarean section in the usual manner at the desired stage of pregnancy. Pre-inoculation bloods were obtained in all instances and the animals were observed for evidence of clinical disease.

Virology. The IHD strain of vaccinia virus with a titer of 10^6.3 TCID₅₀ ml in Vero cells was given intravenously in 2.0 ml amounts. Ability to produce a lesion was determined by intradermal inoculation of the test animal.