Hams believes that deaths caused by EHD explain why last year's whitetail buck harvest was down 30 percent compared to 2011. The mule deer buck harvest was also down, but not due to EHD. Instead, officials blame brain worm (Parelaphostrongylus tenuis) for lower mule deer numbers in 2012, resulting in fewer animals being harvested by hunters. While most whitetails in the eastern part of the country carry brain worms, they rarely kill whitetails. For mule deer, it's a different story. Once infected, symptoms of brain worm are readily detectable, including walking in circles, frequent stumbling and poor coordination and balance. Within a few days, the mule deer is dead.