FHV Infection & L-lysine

Feline herpes virus type-1 (FHV-1) is one of the most common causes of respiratory infections and eye problems in cats. In fact, up to 97% of cats have serological evidence of exposure to FHV-1. Following recovery from primary infection, up to 80% of cats become carriers.

Although carriers can remain asymptomatic for long periods of time, they harbor the virus in the nerve cells. Cats who contract FHV-1 remain lifelong carriers of this highly contagious virus and can easily pass it on to un-infected cats through:

  • Discharge from the nose, eyes, or mouth
  • Litter boxes, water dishes, food, etc.

From the dormant state, FHV-1 may be reactivated and shed throughout the infected cat's life, especially at times of stress.

While there is no cure, you can help your patients get over primary infection and reduce the severity and frequency of recurrences by prescribing L-lysine. L-lysine is an amino acid that, when administered to cats with FHV-1, has been shown to:

  • Lessen the clinical signs of FHV-1 following experimental infection (vs. placebo)
  • Reduce viral shedding in the face of stressors known to induce viral reactivation

Herpes viruses are dependent on arginine, an amino acid that is essential to the development of viral protein. L-lysine competes with arginine, affecting the virus's ability to replicate, consequently reducing the viral load.


  1. Maggs DJ, et al. Evaluation of serologic and viral detection methods for diagnosing feline herpesvirus-1 infection in cats with acute respiratory tract or chronic ocular disease. Journal of the American Veterinary Medical Association, February 1999, 214(4):502-507.
  2. Gaskell RM, Povey RC. Experimental induction of feline viral rhinotracheitis re-excretion in FVR-recovered cats. Veterinary Records, 1977, 100: 128-133.
  3. Stiles J, Townsend WM, Rogers QR, Krohne SG. Effect of oral administration of L-lysine on conjunctivitis caused by feline herpesvirus in cats. American Journal of Veterinary Research, January 2002, 63(1): 99-103.
  4. Maggs DJ, Nasisse MP, Kass PH. Efficacy of oral supplementation with L-lysine in cats latently infected with feline herpesvirus. American Journal of Veterinary Research, January 2003, 64(1): 3-42.