Mini Case Reports: Camelid myelitis

From the December 2020 Newsletter:

Cross-sections of adult nematodes in the spinal cord of a 3-year-old alpaca. Axonal degeneration (arrow) and leukocyte infiltrates (arrowhead) are observed nearby. (H. Pecoraro, NDSU)

A 3-year-old female alpaca was submitted for autopsy. It had a history of parturition (also called “unpacking” or “criating” in this species) the day prior to death. The animal was noted to have been weak in the backend before becoming down and unable to stand. Another alpaca was exhibiting similar signs.

On gross examination, we found hemorrhages in the lungs and intestines and along the tongue. Microscopically, a mononuclear leukocytic infiltrate was noted around blood vessels in the cerebral cortex. Thus, a rabies test was performed and was negative. Given the history of being down, the spinal cord (SC) was removed for histology.

More than 30 cross- and longitudinal sections of the cervical, thoracic and lumbar SC were examined microscopically. One section each of thoracic and lumbar SC had adult nematodes characterized by a 1- to 2-um-thick eosinophilic cuticle, skeletal musculature, pseudocoelom, and digestive and reproductive tracts. Eosinophils and other leukocytes, as well as axonal degeneration, were observed nearby. Encephalitis caused by Parelaphostrongylus tenuis, the meningeal worm of white tail deer, was diagnosed.

P. tenuis infection is one of the main differentials for encephalitis in new world camelids where white tail deer are abundant (for example, northeastern U.S.). This case, however, is the first recorded at the VDL and highlights the importance of parasite prevention. Additionally, P. tenuis infection should be considered in regional alpacas with neurologic signs.