Polyprenyl immunostimulant treatment during experimental feline herpesvirus-1 infection is associated with reduced ocular disease after conjunctival rechallenge

Polyprenyl immunostimulant (PI) was, at the time of this study, a USDA-licensed veterinary biologic for the treatment of feline rhinotracheitis. In two previous controlled challenge trials, PI administration reduced the severity of acute feline rhinotracheitis in specific pathogen-free (SPF) cats (1). We replicated the oral PI challenge-treatment protocol to evaluate humoral and virologic outcomes, measured by serum virus-neutralizing antibody titers and virus isolation, and to assess clinical ocular disease after conjunctival rechallenge. During the study, the frequency of virus isolation and the virus-neutralizing antibody (VN) titers did not vary significantly between the treatment and placebo groups. After the rechallenge, all placebo controls (8/8) developed ocular disease, whereas 10/16 PI-treated cats developed conjunctivitis/ocular disease, and 6/16 remained asymptomatic. PI treatment was associated with a 37.5% reduction in the incidence of ocular disease after conjunctival rechallenge. We hypothesize that PI may reduce the likelihood of clinical ocular disease after FeHV-1 rechallenge by priming innate cell-mediated immune responses.