Table 2 Reasons why cats should not receive lysine supplementation for the treatment or prevention of FHV-1 infection

• Clinical trials with cats failed to show efficacy of lysine supplementation.

• In vitro studies with FHV-1 did not show an inhibitory effect of excess lysine on viral replication.

• Lysine itself does not have antiviral properties, but was believed to act by lowering arginine levels (lysine-arginine antagonism). In cats, excess lysine is unable to lower plasma arginine levels.

• There are no studies showing that intracellular arginine can be lowered to levels that will specifically prevent the synthesis of FHV-1 proteins. Furthermore, it is unlikely that FHV-1 replication in the cat’s cell specifically increases the cellular demand for arginine.

• Arginine is an essential amino acid for cats. Cats deficient in arginine will die as the result of hyperammonemia. No attempts should be made to lower arginine levels in cats, especially not when adding lysine (amino acid) to their diet.

• Lysine supplementation is not effective for the treatment or prevention of herpetic lesions in humans infected with human herpesvirus 1.