Effect of oral administration of L-lysine on conjunctivitis caused by feline herpesvirus in cats

Objective-To determine whether oral administration of L-lysine to cats would lessen the severity of conjunctivitis caused by feline herpesvirus (FHV-1). Animals-8 healthy young adult cats. Procedure-Cats received oral administration of lysine mono hydrochloride (500 mg, q 12 h) or placebo (lactose) beginning 6 hours prior to inoculation of virus. The left conjunctival sac received a 50-mul suspension of FHV-1 grown in cell culture (1.8 X 108 tissue culture infective dose(50)) on day 1. Cats were evaluated and scores given for clinical signs each day for 21 days. Samples for virus isolation were collected from the eye and throat every third day. Plasma lysine and arginine concentrations were measured prior to the study and on days 3, 14, and 22. Results-Cats that received lysine had less severe conjunctivitis than cats that received placebo. Virus isolation results did not differ between the groups. Plasma lysine concentration was significantly higher in cats that received lysine, compared with control cats, whereas plasma arginine concentrations did not differ between groups. Conclusions and Clinical Relevance-Oral administration of 500 mg of lysine to cats was well tolerated and resulted in less severe manifestations of conjunctivitis caused by FHV-1, compared with cats that received placebo. Oral administration of lysine may be helpful in early treatment for FHV-1 infection by lessening the severity of disease.