Is Dietary L-Lysine Effective for Treatment of Feline Ocular Disease Caused by Feline Herpesvirus-1?

Abstract

Since the early 2000s, oral supplementation of L-lysine has been used to treat ocular disease in cats that was attributable to feline herpesvirus (FHV). Local (ocular) signs of disease that included conjunctivitis, blepharospasm, and ocular discharge were felt to improve when oral supplementation with a 250 or 500 mg bolus was administered once to twice daily. FHV-1 is considered the most common pathogen among other infectious agents, i.e., feline calicivirus and Chlamydophila felis, to cause ocular disease as well as infectious upper respiratory disease. It is felt that FHV-1 may establish a lifelong neural latency in 80% of infected cats. Early studies proposed that oral bolus administration of L-lysine reduced replication of FHV-1 by approximately 80% via antagonism of arginine, an essential amino acid for FHV-1 replication. Arginine is an essential dietary need for normal cat immune function. Studies evaluating serum arginine levels following oral L-lysine dose trials have found no adverse diminished levels of arginine. L-lysine is commercially available over the counter for treatment of the common cold sore in people that is caused by herpes simplex virus type 1. This formulation may be used for treatment of feline ocular disease by administering pills orally or by adding the contents of capsules to the diet. The generally recommended dose is a bolus of 500 mg, per os, twice per day in adult or average sized cats. Younger or smaller cats are typically fed 250 mg, twice per day. It has been shown that diets fortified with L-lysine that are consumed gradually throughout the day may not provide the immunologic effect necessary to reduce ocular disease and, specifically, infectious upper respiratory disease. Since the emergence of L-lysine as an effective and safe, long-term therapeutic for FHV-1 treatment, a number of commercially available products have become available on the veterinary market. By using palatable gels and treat products, administering a consistent and effective dosage regimen has become less problematic.