Is Your Kitty Having an FHV Outbreak? Why Giving Lysine Can Be Dangerous

The last time you got a cold sore -- also known as herpes simplex 1 -- someone may have suggested that you take an amino acid called lysine. And if your cat is diagnosed with feline herpesvirus 1, or FHV, you may wonder if lysine can help control outbreaks in your kitty, too. That can certainly sound more appealing than expensive antibiotics and antiviral treatments that can have side effects.

What is feline herpesvirus 1?

First of all, feline herpes, or FHV, doesn't actually cause sores on your cat's face. Instead, it causes some pretty nasty upper respiratory symptoms, similar to influenza -- some people even refer to it as "cat flu."

FHV is very contagious and can be spread through just about any type of contact between cats. In addition, once an animal has had the virus, they continue to carry it in a dormant state. Every once in a while, when the kitty's immune system gets stressed, it can become active again. Though it rarely results in severe symptoms again for the infected cat, it can be shed and make other animals sick.

Is there any research to show that lysine works?

The way that lysine works in humans to suppress herpes simplex is to block the absorption of another amino acid called arginine. The herpes virus requires arginine in order to replicate. So the idea of giving lysine initially seems like a good treatment to try.

However, while there may be some validity to lysine working in humans, a recent study conducted by University of California Riverside researchers found that cats process arginine very differently than humans. Even if lysine has some effect on treating FHV, it could be dangerous to give it to your kitty because of the way it inhibits arginine production. Because cats don't synthesize arginine in their bodies like humans can, the lysine-caused deficiency in arginine can result in an inability to break down protein in the body, leading to serious illness and even death.

What are some other treatments for FHV?

The easiest "treatment" for FHV is to avoid getting it in the first place. A series of vaccines exists for cats that starts at eight weeks. Then, you get your cat a booster at one year and every one to three years after. 

But if your cat does get infected, there are a couple of treatments recommended by veterinarians. 

  • Oral medication. Famciclovir is an antiviral drug used in humans to quell herpes outbreaks. It's given orally and can help reduce severe symptoms.
  • Eye drops. There are a few different types of ocular antiviral drops that are recommended if your cat develops an eye infection as part of the FHV illness. Drug names include idoxuridine, trifluridine and cidofovir.

The best way to manage FHV in your cat is to get it vaccinated as part of a well-cat program you manage with your vet. If you do think your cat is showing signs of an illness like FHV, see your vet, such as University Pet Hospital, right away and start an established antiviral treatment.