Naturally Occurring Parelaphostrongylus tenuis–Associated Choriomeningitis in a Guinea Pig With Neurologic Signs

An adult male guinea pig (Cavia porcellus) with a 1-month history of hind limb paresis, torticollis, and seizures was euthanized and submitted for necropsy. Gross examination was unremarkable, but histologic examination revealed multifocal eosinophilic and lymphoplasmacytic choriomeningitis and cross sections of nematode parasites within the leptomeninges of the midbrain and diencephalon. Morphologic features of the nematode were consistent with a metastrongyle, and the parasite was identified as Parelaphostrongylus tenuis by polymerase chain reaction testing and nucleotide sequencing. Further questioning of the owner revealed that the guinea pig was fed grass from a yard often grazed by white-tailed deer (Odocoileus virginianus). To the authors' knowledge, this is the first report of a naturally occurring P. tenuis infection in a guinea pig. A 2.5-year-old male guinea pig (Cavia porcellus) was eutha- nized and submitted for necropsy following a 1-month history of progressive neurologic signs, including hind limb paresis, torticollis, and seizures. Treatment included calcium, vitamin C injections, prednisolone, and buprenorphine. The guinea pig was purchased from a pet store 2 years earlier and was fed a commercial diet supplemented with a variety of fruits and vegetables, including grass from a yard frequented by white- tailed deer (Odocoileus virginianus). For approximately 5 months prior to the onset of clinical signs, the guinea pig was housed with another healthy young male guinea pig. There was no history of trauma. Differential diagnoses for neurologic disease in guinea pigs include trauma, pregnancy toxemia, hypocalcemia, and bacter- ial otitis/meningitis. Neurologic disease associated with Bayli- sascaris procyonis migration has been reported in guinea pigs housed on shavings contaminated with raccoon feces. 16 Although neoplastic disease is uncommon in guinea pigs, tumor metastases to the central nervous system (CNS) would be an important differential for an animal with multicentric neurologic deficits, as in this case. A complete necropsy was performed. The calvarium was opened and the brain fixed in situ for sectioning. The entire vertebral column was fixed and decalcified, and representative cross sections were trimmed for histopathology. No gross lesions were detected during the necropsy; however, micro- scopic examination revealed cross sections of nematode parasites (Fig. 1) within the leptomeninges covering the midbrain, associated with eosinophilic and lymphoplasmacytic choriomeningitis (Fig. 2). The nematodes were 100 to 200 mm in diameter, with a thin, smooth cuticle; coelomyarian muscu- lature; accessory hypodermal chords; and a large gastrointest- inal tract composed of few multinucleate cells. Cross sections also contained a genital tract with either sperm or thin- shelled eggs. Multifocally, the leptomeninges of the brain and spinal cord and the choroid plexus were expanded by moderate infiltrates of eosinophils, macrophages (often containing brown cytoplasmic pigment), plasma cells, and fewer lymphocytes. In the cross section of the vertebral column at the level of T12, there were multifocal areas in all funiculi characterized by dilated axon sheathes and swollen axons. In the vertebral col- umn section at the level of L3, the spinal cord was unremark- able, but within the epaxial and hypaxial skeletal muscles, there were multifocal areas of myofiber degeneration and a focal area of heterophilic myositis. Based on histologic features, the nematode within this gui- nea pig's leptomeninges was classified as a metastrongyle. The meningeal distribution of the parasite and the history of