Experimental infection of mule deer with Parelaphostrongylus tenuis

Six adult and three fawn mule deer (Odocoileus hemionus) were experimentally infected with a range of 75-100 infective larvae of Parelaphostrongylus tenuis. Five of the six adult deer developed clinical signs of neurologic disease that terminated in paralysis between 35 and 80 days. The sixth deer developed slight signs of neurologic disease for 10 days, but recovered. All three mule deer fawns developed neurologic disease. Adult meningeal worms were recovered from the subdural space of the spinal cord of two fawns. Eggs were observed on the cranial dura mater of one of these fawns, indicating that P. tenuis can complete its life cycle provided mule deer can survive the damage resulting from the infection. Neither eggs nor larvae of P. tenuis were recovered from the feces or lungs of infected mule deer. Clinical signs and histologic lesions observed in experimentally infected mule deer resembled those reported in infected moose (Alces alces americana). Two critical periods were apparent in mule deer infected with P. tenuis: nematode migration through the spinal neural parenchyma, and penetration of the adult nematodes into the cranial neural parenchyma. While most adult deer were unable to survive the first critical period, fawns survived the first but succumbed to infection during the second critical period.