Herpes simplex virus type-2 infection by a footpad route results in neuronal death in mouse spinal ganglia

We have examined the effects of herpes simplex virus type 2 (HSV-2) infection on neuron numbers in mouse dorsal root ganglia (DRG) following unilateral hind footpad inoculation. One month following HSV-2 strain MS inoculation, tissue sections of decalcified spine containing the paired 4th and 5th lumbar DRGs were stained with cresyl violet. Neuronal numbers, somal areas and ganglion volumes were determined for ganglia ipsilateral and contralateral to both HSV-2 and medium inoculations. One month following HSV-2 infection, 47–88% of neurons disappeared in the ipsilateral ganglia. The somal areas of the remaining neurons in these ganglia fell within the range of the uninfected population. Ganglionic shrinkage did not occur as a result of HSV-2 infection; neurons were replaced by large numbers of inflammatory cells. Neuron numbers in the contralateral control ganglia of the HSV-2 inoculated mice appeared slightly decreased. Mice inoculated with medium contained similar numbers of neurons in ipsilateral and contralateral ganglia. These results show that, in addition to other previously described host alterations, infection with HSV-2 strain MS results in neuronal death in the affected host ganglia. This is the first in vivo quantitative documentation of neuronal death induced by herpes simplex virus infection.