Retrospective study of central nervous system lesions and association with Parelaphostrongylus species by histology and specific nested polymerase chain reaction in domestic camelids and wild ungulates

Formalin-fixed, paraffin-embedded tissues from elk (Cervus elaphus), goats, and camelids with case histories and lesions suggestive of Parelaphostrongylus tenuis were examined by histology to characterize lesions that could aid in definitively diagnosing P. tenuis infection. Additionally, sections of paraffin-embedded tissue were used in a nested polymerase chain reaction (nPCR) using Parelaphostrongylus-specific primers to determine how PCR results corresponded with histological findings. Histological changes in brain and spinal cord consisted of linear tracks of hemorrhage; tracks or perivascular accumulations of hemosiderin-laden macrophages; acute foci of axonal degeneration and/or linear glial scars; and perivascular, parenchymal, or meningeal accumulations of eosinophils and/or lymphocytes and plasma cells. Of the 43 samples with histologic lesions consistent with neural larval migrans, 19 were PCR positive; however, only 8 were confirmed Parelaphostrongylus by DNA sequencing. Additionally, 1 goat was identified with a protostrongylid that had a 97% identity to both Parelaphostrongylus odocoilei and a protostrongylid nematode from pampas deer (Ozotoceros bezoarticus celer) from Argentina. None of the histologic lesions individually or in combination correlated statistically to positive molecular tests for the nematode. The results indicate that it is possible to extract Parelaphostrongylus DNA from formalin-fixed, paraffin-embedded tissue, but extended fixation presumably can cause DNA crosslinking. Nested PCR provides another diagnostic tool to identify the cause of neurologic disease in camelids and elk with histologic lesions consistent with neural larval migrans. Furthermore, potential novel protostrongylid DNA was detected from a goat with lesions consistent with P. tenuis infection, suggesting that other neurotropic Parelaphostrongylus species may occur locally.