Case report: Halicephalobus gingivalis in a Tennessee pony.

A 17-year-old female grade pony presented to University of Tennessee Veterinary Medical Center in May of 2021 for evaluation of multifocal, firm, sessile, circular lesions of various diameters on the ventrum and flank. The lesions had been present for two weeks at presentation. An excisional biopsy found numerous adult and larval rhabditid nematodes most consistent with Halicephalobus gingivalis. PCR targeting a portion of the large ribosomal subunit confirmed this diagnosis. The patient was treated with a high dose course of ivermectin followed by fenbendazole. The patient began showing neurologic signs five months after initial diagnosis. Due to the poor prognosis, euthanasia was elected. PCR of CNS tissues confirmed the presence of H. gingivalis in the brain, and one adult worm and several larvae were found on histologic sections of the cerebellum. H. gingivalis is a rare but lethal disease of horses and people.