How annoying is a cold sore?
Now imagine having one on your eyeball.
The class of viruses known as Herpes are tricky; they play a great game of hide-and-seek. They retreat into and set up camp in the nerve endings, where the immune system can not find and fight them. This is why people afflicted with Herpes virus have to contend with outbreaks their whole lives – whether we are talking about the pain-in-the-lip form known as cold sores, or about genital Herpes.
Cats suffer from a Herpes virus in all its recurrent glory too – Feline Herpes Virus, or FHV. In cats, it is primarily a respiratory virus. The most common patients are kittens, who have immune systems too inexperienced to kick out the virus before it gets a toe-hold. These kittens can be sick to varying degrees: some just basically have a “head-cold”, some can have such severe upper respiratory disease that they can’t eat or breathe properly.
So what makes FHV such a particularly nefarious virus?
One charming characteristic of the virus is that it can eat its way through the surfaces of lips and tongues to cause ulcerated sores. This has a lot to do with why the severely affected kittens don’t eat – it just hurts too much.- Eyes. Ouch. Just – ouch. It’s bad enough when the virus inflames the skin and inner linings (conjunctivae) of the eyelids and eye sockets. Affected kittens have painful red eyes that often end up sealed shut by swelling and discharge. But it is worse when the virus colonizes the cornea, the clear window over the front of the eye. This does happen in people too – my own partner recently had his first exposure to the cold sore virus (don’t ask me how someone makes it to his forties with no cold sores…), but instead of causing a lip ulcer, the virus went right into his cornea. So I can report from an actual human’s point of view that herpes in your eye really hurts.
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Pickles’ Story: I recently treated a 9 year old cat, Pickles, whose eye became suddenly clouded over and painful. A dye we use to show up breaks in the cornea, called fluorescein, showed nothing – the problem was in the “glass” of the window itself, not on the surface. By a couple of days later, Pickles’ cornea had effectively melted, and was sagging down and bulging forward. Behind it, in the front chamber of the eye, was a big glob of protein material – the same kind of protein that is in the ooze from a skinned knee, that the body uses to try and patch and repair itself. We managed not to have the eyeball rupture, and the eye has healed to the point where it is not painful anymore – but that eye will never be the same again.
- The Forever Factor. When the virus first enters the eyes and respiratory tract, there is a chance for the immune system’s antibodies (if it has any made) to shackle the virus, and not let it go further. If the virus is tangled up in an antibody, it is held and marked for immune cells to swallow and digest it. BUT… if the virus gets a chance to invade and colonize tissues before any antibodies hobble it, then it finds its hiding place. Herpes viruses are neurotropic – this means they have a special ability to find and latch on to nerve tissue, and insinuate themselves right into the nerve fibres. Hiding in here, the viruses are invisible to the immune system. If the immune system has good vigilance, and has learned how to make anti-herpes virus antibodies, then it can trip up and stop any virus that dares to emerge. However, if the immune system is not doing such a good job, if it is impaired by stress hormones, fading with age, or busy fighting something else, then the virus can show itself again. This could be what happened with Pickles – he may have had that virus hanging on since he was a tiny kitten.
So, what do we do about FHV?
- Train the immune system. This is where vaccination comes in; FHV is one of the 3 respiratory viruses in the core vaccine we give to cats. If we teach a kitten how to fight the virus before it ever tries to enter, then the infection will never get established in that kitten’s tissues. If the virus has already made its way in and found its hidey-holes, then vaccination gives the immune system the tools to keep it in hiding. Every time the virus tries to emerge, the antibodies will jump it, limiting or even preventing an outbreak.
- Trick the virus. Virus replication involves having the virus’s genetic code hijack cell machinery, causing the cells to make more copies of the virus. An important ingredient of this process is the amino acid called Arginine. There is another amino acid that is a “look-alike” for Arginine, called Lysine. If we give the cat extra Lysine at the first sign of an outbreak, we can short-circuit the outbreak. The virus grabs on to the Lysine, mistaking it for Arginine, and thus is unable to complete repication.
- Fortify! This means keeping your infected FHV cat in an optimal state of health. Well balanced, digestible diet; regular vet check-ups, to catch illnesses before they get too far; and, if possible, keeping you cat as an inddor kitty, with less exposure to illnesses or injury.