April 2016
From the State Vet's Office

Equine Herpes Virus Type 1

And Other Things That Go Bump in the Night

I think about animal diseases a lot. That’s probably a pretty obvious statement since I am a veterinarian. But, not being in private practice for a long time, I have trimmed the list of diseases that cross my mind frequently. Take a disease such as canine parvovirus. Other than vaccinating my own dogs against the disease, I never really think about it. I think about diseases that we have some kind of regulatory authority over nearly every day. I think about certain foreign animal diseases that, if they enter our country, could devastate our state. Then there are those diseases we do not directly regulate, but have the potential to have an extremely detrimental effect on our economy. Those diseases come on and off my radar screen. One of those diseases is the neurological form of equine herpes virus type 1. Actually the disease is often referred to as Equine Herpesvirus Myeloencephalopathy. The virus affects areas of the brain and spinal cord.

If you tend to follow EHV1 outbreaks, you will be aware that there are occasional outbreaks of the disease in various locations and states around the United States. In Alabama, we have been, so far, fortunate to have escaped having a problem with the neurological form of the equine herpes virus.

EHV1 manifests itself in four ways. They are neurological signs, abortions, respiratory infection and neonatal deaths. In the past, the importance of the virus centered on the abortions associated with horses infected by the disease. According to an USDA information sheet, EVH1 meets one of the criteria for an emerging disease. It states that an emerging disease "changes in severity, type of animal that can be infected or other changes in pathogen behavior." It seems the nature and the severity of the EVH1 infection have changed. It’s possible, however, that the number of cases reported involving neurological signs has increased instead of the actual number of cases occurring. The debate on that issue will be settled somewhere down the road when more data becomes available.

Also, if you follow the cases of the neurological form of EHV1, you will know there have been cases this year in Texas, New Mexico and New York. And you will probably know the University of Georgia Teaching Hospital was temporarily closed due to having a horse with neurological signs testing positive for EHV1. While there are worse things that can happen, having to close a veterinary hospital temporarily certainly puts a kink into "business as usual." There have been several very large equine events in other states canceled because of the presence of the disease.

I know what many of you are thinking right now, so let me fill everybody else in. You are thinking, "We vaccinate every year against rhino, so why should we be concerned. It is the same virus." Well, I’m glad you asked because I asked that same question myself a few years ago when we began hearing about these outbreaks of EHM. The problem is that the vaccine seems to work well to protect against the respiratory form and abortions, but, possibly because of slight mutations in the virus, vaccinated horses are often those stricken with the disease.

The nature of herpes viruses makes them especially aggravating to deal with. Let’s leave the equine species for a minute here and think about how herpes viruses affect humans. If you have ever had shingles or know someone who has had shingles, you know the disease is caused by the virus that has been hanging around in your body since you had the chicken pox back in second grade. It’s the same deal with fever blisters. If you had fever blisters when you were a kid and still have one occasionally after some period of stress, those blisters are not caused by a new virus each time. It is the same virus that makes the big sore on your lip – usually right about the time you have to get your driver’s license renewed, so you get to be reminded about it for the next four years. Herpes viruses tend to come in and cause the initial infection of whatever their host is, and then just stick around for the rest of the hosts’ lives so they can surface again years, maybe even decades, later and wreak havoc. But as a friend of mine once asked, "What is time to a virus anyway?"

EVH1 is considered to be mostly spread by horse-to-horse contact. It can also be spread by fomites and possibly by aerosol. The distance that the virus may be spread by aerosol is not known. The virus is often spread via aborted fetuses and fetal membranes. Horses may appear perfectly healthy, yet still shed the virus.

Prevention of EHM, the neurological form of EVH1, can be prevented by using strict biosecurity. This is especially important for horses that travel to events, sales or are otherwise comingled with other horses. It is important that horses not share equipment. It is also important to make sure workers wash hands between handling equipment or horses if there is a possibility of exposure. Horse owners, especially those who attend events, should keep up-to-date on where outbreaks have occurred.

The signs of the disease are typical of most neurological diseases. Some of these signs include fever preceding neurological signs, lack of coordination, dribbling urine, loss of tail tone, posterior paresis, lethargy and becoming unable to rise. It is important for all neurological diseases in horses and other animals to be reported to the State Veterinarian so zoonotic diseases (diseases that can be transmitted between animals and man) such as eastern equine encephalitis, West Nile virus and rabies can be determined. EHV1 can be diagnosed by a test know as PCR from nasal swabs or through serology.

If you have questions about EHM or EVH1, contact your local veterinarian or my office. My phone number is 334-240-7253.



Dr. Tony Frazier is the State Veterinarian for Alabama. You can contact him at 334-240-7253.