Dogs infected with unmodified VEE developed fever, viremia, and leukopenia. Seven of the dogs infected failed to manifest frank clinical signs of illness. The remaining three dogs became somewhat aggressive toward the other dogs and less receptive to handling; no other frank signs of illness were observed. The infection was fatal for two of the three. Microscopic examination of the brains of these two animals failed to reveal evidence of encephalitis even though virus was recovered.
The attenuated strain caused an inapparent infection detectable only by serologic methods. The infection resulted in immunity to subsequent challenge with unmodified virus.