A Comparison of Neurovirulence of Vaccinia Virus by Intrathalamic and/or Intracisternal Inoculations into Cynomolgus Monkeys

The authors have studied the virulence of several vaccinia virus strains by intrathalamic (i.t.) inoculation into cynomolgus monkeys for the purpose of analysing the pathogenesis of postvaccinial encephalopathy or encephalitis (1, 3). Before these studies, we performed a quantitative comparison of the neurovirulence in monkeys by i.t. and/or intracisternal (i.c.) inoculations with Lister strain as well as CV 1 strain of vaccinia virus. The reference Lister (calf lymph) vaccine and the CV 1 vaccine which was kindly provided from Dr. C.H. Kemp, University of Corolado, were grown in the chorioallantoic membrane (CAM) of 11 to 12 day eggs. The virus was purified. from CAM homogenates by fluorocarbon treatment and sucrose gradient centrifugation, and adjusted to 4 •~ 108 PFU/ml. Monkeys were inoculated intrathalamically and/or intracisternally with 0.5 ml each of serial 10-fold dilutions of the virus. Nine monkeys were used for each experiment and three monkeys for each dilution. The mortality of the monkeys inoculated with each virus strain and by the different inoculation routes, is summarized in Table 1. With the Lister srain the mortality of the monkeys inoculated intrathalamically was slightly higher than that by the i.c. route. Furthermore, there was no clear difference in the mortality between the i.t. inoculation and combination of both i.t. and i.c. routes. This led the authors to use i.t. inoculation only in further experiments as described elsewhere