Antiviral effect of poly(styrene 4-sulfonate) (PSSNa) on feline calicivirus oral infections in cats—field study

Feline calicivirus (FCV) infection causes nasal discharge, oral mucosa inflammation, ulcerations, gingivitis, and conjunctivitis, often progressing to chronic gingivostomatitis, severe pneumonia, and fatal systemic infections. With no antivirals currently available, poly(sodium 4-styrene sulfonate) (PSSNa) was identified in 2019 as a safe inhibitor <i>in vitro</i>. In this preliminary single-center, randomized, double-blind, placebo-controlled field study, we further characterized the PSSNa's safety profile and tested its efficacy in cats after topical oral application. Twenty-eight cats were enrolled in the study, and they were initially treated with standard dental therapy, followed by adjuvant local oral application of PSSNa or placebo. After 4 weeks, PSSNa demonstrated a favorable safety profile with no adverse effects. The treatment group showed a significant decrease in viral load (<i>p</i> = 0.001) compared to placebo (<i>p</i> = 0.012). Disease symptoms improved significantly, though the oral health index remained unchanged. Additionally, PSSNa showed activity against multiple genetically diverse isolates, indicating a potential, exploratory link between genetic background and treatment outcome. Summarizing, this study presents initial data on the efficacy and tolerability of PSSNa treatment for FCV infections in cats. Nevertheless, several significant limitations should be acknowledged, including inconsistent drug administration by owners, non-sterile housing, sample size, variable oral disease severity, and concurrent treatments.