This week I’m at a veterinary conference in another state. One of the lectures I attended on this same topic started up with news about Oregon — another horse with EHV-1 has been euthanized. It’s not a great honor, but not our fault.
Several cases have recently shown up in our state. EHV-1, or Spinal Rhino is a herpes virus, which makes it a kissing cousin to the virus that gives us humans cold sores. EHV-1 is the virus that causes Equine Herpesvirus Myeloencephalopathy – or EHM for short, because that’s a mouthful.
The human and the horse versions of this virus behave similarly, in that nearly everyone is already infected with the virus (about 80% of horses have it by age one). Most of the time it just hangs out, not doing much of anything, but it reappears whenever we are stressed (like for a job interview and you get a cold sore). In horses, being stressed often means going to a horse show, or being trailered.
EHV-1 will also cause mares to abort and is the cause of some stillborn foals. This is what the Broodmare Rhino vaccines at 3-5-7-9 months of pregnancy are trying to prevent. It also causes respiratory disease, and a fatal neurologic disease. EHV-1 will not infect you, which is why it’s called Equine Herpes virus.
Stress will allow those latent, or inactive infections to come out of hiding. Once that happens the virus can start replicating in the throat where it can be easily spread. At first, horses will have a fever (a rectal temp above 101.5 degrees F), but this fever is often missed. Two to ten days later, for some unlucky horses, the neurologic signs may show up.
Often, the respiratory infection is all that happens – it clears up and goes back in hiding again. But now that Fluffy is coughing all over, she can easily infect Ol’ Blue, who lives in the next stall.
A couple of days later, Ol’ Blue might not be so steady on her legs, and might start dribbling urine.
The vet comes out, and makes “that face,” and takes nasal swabs, and draws blood, and quarantines the entire barn. Everyone holds their breath until the lab results come back. Yep, Ol’ Blue has EHM.
Now what?
Everyone will want to load their horses up and scatter to the wind. Please don’t. That’s how the disease spreads, and how it inflicts anxiety and worry onto other horse owners.
Step one is to isolate Ol’ Blue and any other horse that has a fever. Those horses will be cared for in a separate area. Everyone else has the pleasure of taking their horse’s temp twice a day. Mind you, the closest I have come to death as a veterinarian is trying to take temps on horses, so be careful!
This continues for 28 days. If a horse with a fever is found, it is put into isolation and the clock starts over for all of the horses. This is called the “Time Out” strategy.
There’s also the “Test Out Strategy.” It starts the same, isolate Ol’ Blue and the rest of the sickies, and then do the temp dance twice a day on everyone else. But in this strategy, on day 14, everyone gets a swab and blood test. If everyone is negative the quarantine is over! Yay!
The trouble is, no one ever gets a group of horses to all test negative. So those horses are isolated and the clock starts over. I mention this strategy only because I know someone will ask. Yes, we can do it, but most likely it’s more expensive and takes just as long — or even longer.
So why do we bother vaccinating? You ask — a little anger glinting in your eyes. Good question!
Horses that are vaccinated spread less virus to their stablemates. None of the EHV-1 vaccines claim to prevent the neurologic form, but some vaccines are more helpful than others.
Types of Vaccines
There are two types of vaccines. Killed – where the infectious agent is dead but the antigens are still intact and will cause the horse to mount an immune response. The other is Modified Live (MLV). In this vaccine the bug has been altered, but not killed. Or a different virus is used but it’s been “decorated” with the antigens of the offending virus. So it can’t cause disease. Let me repeat: a MLV vaccine will not cause an EHV infection or EHM.
The advantage of the MLV vaccine is that it has a faster response and a slightly different response than the killed vaccine. The difference is that instead of just causing antibodies to be formed, it also wakes up killer T cells. These killer cells are more effective at protecting against the neurologic disease, EHM.
It doesn’t say it on the package, and the drug company isn’t going to pay a claim if you use an MLV vaccine and your horse gets Spinal Rhino anyway, but it’s the best option out there.
The best way to protect your horse is to be smart at shows and other stressful events. The virus is spread via respiratory secretions and it spreads easily. So don’t hang out at the ingate, letting Fluffy touch noses and squeal at every other horse in range.
Put tack stalls on either end of your team’s row. That will put extra distance between your horses and the snotty-nosed colt that has no business being at a show to begin with.
Also, don’t be a fomite. What’s a fomite, you ask? It’s anything that can carry an infectious agent around and spread it without getting sick itself. Some fomites are easy to avoid, like bringing your own water buckets. Others are more difficult, like stable flies, your dog, or even you. Anything you touch could transfer the virus to your horse, so when you go back to pet your horse you might have delivered the virus. Don’t be a fomite, wash your hands.
The virus can survive for a week on surfaces, but under ideal conditions it can hang on for a month. Nice. Hand-washing and most disinfectants will kill it.
This is a “reportable disease” – so I am required to tell the State Vet if your horse tests positive. Sorry, it can’t be our little secret.
If you have any other questions, be sure to speak with your vet.
