Successful Treatment and Long-Term Follow-Up of a Young Cat with Neurological Feline Infectious Peritonitis (FIP) Using Remdesivir

Background: Feline infectious peritonitis (FIP) has long been regarded as a fatal disease, most commonly affecting young cats in multi-cat environments. Although its pathogenesis is not yet understood, the virulent biotype (FIPV) is caused by a mutation of the feline enteric coronavirus (FCoV) with changes in-cell tropism from enterocyte to monocyte. Immunohistochemistry remains the gold standard for diagnosis; However, a combination of clinical signs and effusion analysis, if present, including cytology, biochemistry, and FCoV RNA PCR testing can strongly support a diagnosis of FIP. Abdominal effusions, lymphadenopathy, pyogranulomatous lesions affecting abdominal organs, eyes and central nervous system are some of the common findings in wet and dry forms. Renal architecture and as well as functional abnormalities are reported to be common in younger cats including renomegaly, bilateral or unilateral, cortical hyperechogenicity, medullary rim sign, pyelectasia, and loss of corticomedullary differentiation. Poor prognosis and high fatality rate anecdotally associated with FIP have improved considerably in recent years due to the novel use of nucleoside analogues, which have been successful in achieving clearance and complete long-term resolution of clinical signs. Remdesivir and GS-۴۴۱۵۲۴ are among the most effective and widely used antiviral drugs currently available for the treatment of FIP. Although their efficacy and clinical success are still under investigation, current evidence suggests that GS-۴۴۱۵۲۴ may be more effective in treating the neurological and/or ocular forms. Case Summary: A ۷-month-old female domestic shorthair cat was presented with a progressive history of tetraparesis, uveitis, severe cachexia, and anorexia over ۴-day. Serum biochemistry and hematologic evaluation revealed non-regenerative anemia, lymphopenia, neutrophilia, hypoalbuminemia, and hyperglobulinemia (A/G ratio = ۰.۱۰). Abdominal ultrasonography demonstrated mesenteric lymphadenomegaly, nephropathy, and urinary bladder sediment, but no free fluid. Feline infectious peritonitis was suspected, and RT-PCR and Real-time PCR were performed on whole blood and rectal swabs to detect and characterize FCoV. The cat was treated with thiamine (vitamin B۱), vitamin E, omega-۳ fatty acids, and remdesivir. Although GS-۴۴۱۵۲۴ would have been the preferred choice for treating this patient, remdesivir was selected instead due to financial constraints. Neurologic signs improved significantly after five subcutaneous injections of remdesivir. The cat received an ۸۴-day course of remdesivir (۱۰ mg/kg). At the time of manuscript preparation (more than ۱۵ months after treatment) the cat remains ambulatory, seizure-free, and without recurrence of ocular signs or detectable viral shedding in feces.