Following intracerebral inoculation, the DA strain of Theiler's virus seque
ntially infects neurons in the gray matter and glial cells in the white mat
ter of the spinal cord. It persists in the latter throughout the life of th
e animal. Several observations suggest that the virus spreads from the gray
to the white matter by axonal transport. In contrast, the neurovirulent GD
VII strain causes a fatal encephalitis with lytic infection of neurons. It
does not infect the white matter of the spinal cord efficiently and does no
t persist in survivors. The inability of this virus to infect the white mat
ter could be due to a defect in axonal transport. Using footpad inoculation
s, we showed that the GDVII strain is, in fact, transported in axons. Trans
port was prevented by sectioning the sciatic nerve. The kinetics of transpo
rt and experiments using colchicine suggested that the virus uses microtubu
le-associated fast axonal transport. Our results show that a cardiovirus ca
n spread by fast axonal transport and suggest that the inability of the GDV
II strain to infect the white matter is not due to a defect in axonal trans
port.