11/21/2025
Rhinopneumonitis/Equine Herpes
With the recent cases in Texas, Oklahoma and now Colorado there is no reason to panic. YET if you have your horse in a show barn where there are other horses coming in/out and going to shows at this time we do recommend you call the clinic and we can dispense one of the vaccines that helps alittle bit more than the others for the neurological virus. The Vectra Gold that we use is the "3rd best vaccine out there" and if only your horses are at home this is adeqate at this time. This vaccine that we dispense is a killed vaccine.
Rhinopneumonitis is a cold virus that commonly affects horses. Rhinopnumonitis is also called Equine Herpes virus. Herpes is only a classification of viruses; there are many types of herpes. Other animals can also have herpes viral infections, but it is not likely for the equine rhinopneumonitis to be transmitted to other species (except possibly the camelids). The equine herpes/rhino viruses had been classified as Type 1, Type 2, Type 3 and Type 4. There are 7 strains of herpes that affect horses. This handout is for the alphaherpesvirus diseases. The type 5 herpes, a gammaherpesvirus, is not very common and causes equine multinodular pulmonary fibrosis. The equine herpes viruses do not affect humans. Usually only infect one species of animals is affected by a herpes virus; the exception is the equine herpes/rhinopneumonitis and members of the camel family (alpacas, llamas, etc). With some newer strains of the Equine Herpes 1/Rhino some bears, guinea pigs and gazelles have developed serious problems from this virus; guinea pigs do not need to be vaccinated with equine rhinopneumonitis.
The type 1 Herpesvirus is the most destructive of the varieties. It causes abortions, respiratory colds, and sometimes myelocencephalopathy (EHM) if the nerves are being affected. Abortions are usually in late pregnancy; and if near foaling a very weak foal is produced. The virus is spread by nasal discharge and aerosol coughing in the air. After being exposed it usually takes 5 7 days before the horse will show the flu like signs, or nasal discharge. If diagnosed this equine herpes/EHM/EHV1/rhinopnuemonitis is a reportable disease. A horses need to have close contact to be able to spread the disease. The virus usually affects the younger horses, with older horses usually only showing mild cold signs. A high abortion rate is encountered with this virus, which is why we recommend a 3+ vaccination program for all mares during their pregnancy. You should not get into a habit of routinely trading food and water buckets in barns with pregnant horses. Diseases can be spread by the rotation of equipment among different animals. Because many horses can have latent infections and carrier shedding, this disease appears fairly frequently in barns and stables.
If there is a neurological outbreak, the premises may be quarantined and all horses will be individually nasal swabbed for a PCR testing. This expensive PCR test is not routinely done with a horse showing the flu signs or a neurological problem, as there are many other diseases which can show the same signs. EQUID is a term which some refer to with the equine herpes I neurological disease; equine herpes myelocencephalopathy (EHM) is another term. A nasal swab from a horse with a high fever and nasal discharge may be indicated to diagnose herpes in an outbreak. The nasal swab uses a PCR test for the virus.
The equine rhino virus type 1A usually affects younger horses as an upper respiratory disease; it is also called ERAV. Unless PCR type tests are done it is difficult to distinguish between the different rhino like viruses causing flu type problems. ERAV is almost a different virus as it is has been classified as an Apthovirus (previously a picorna virus); the regular rhinoviruses have been reclassified as Erboviruses by 2012 and it will be years before we all get accustomed to the new terminology. There is a vaccine for EHRV.
Equine Herpesvirus Type 2 causes inflammation of the eyelids and in the back of the mouth. It also can cause pneumonias in foals. Equine Herpesvirus Type 3 is a venereal disease, transmitted sexually. It causes ulcers and pustules around the mare's va**na and sometimes elsewhere. It rarely causes abortions. We advise not breeding the mare for 1 month if she has signs of a herpes virus. There are topical medicines available to treat these sores. Equine Herpes virus type 4 (EHV-4) usually limits itself to lung infections and cold type symptoms.
Vaccinations for horses are available for type 1 and 4 herpes. The vaccine is commonly is called Rhinopneumonitis. We advise vaccination of all younger horses for this problem up to twice a year. After the 2nd year of age, the vaccine program will depend upon whether the horse is in a stable, in horse shows or if in a group setting with other younger horses being transferred in and out. The USEF requires proof of vaccination for Rhino and also Influenza every 6 months in order to help reduce the neurological outbreaks that are associated with horse shows (2015+). Unfortunately there is no vaccine labeled to prevent the Herpes 1 neurological problems, yet there are vaccines labeled for the abortion and respiratory issues. A vaccine will not totally protect the horse from the neurological form, yet we do have some vaccines that “are better than others” for EH-1 in reducing neurological signs and severity of the disease if infected. Once an animal is infected it may be a carrier for life, similar to herpes in humans. Stress such as temperature extremes, horse shows, etc., may cause the virus to become active again. It is difficult to make an effective vaccine for herpes, especially when the virus can involve the nervous systems where antibodies and white blood cells are not normally found. We also recommend periodic vaccination of the camelid family for Rhino, using the equine vaccine, especially if the alpaca and llamas go to shows and events.
The disease is usually sporadic, only rarely will a lot of horses together show an outbreak. The horse usually has a temperature of 102 104 degrees before showing the rhinitis (upper respiratory signs). The blood tests for infections usually are fairly normal, although in the early stage we may see a low lymphocyte count. We usually do not need to run blood tests on the average horse showing signs of the flu, unless the signs are severe. Occasionally we'll see a horse that has the neurological problem; these horses will have trouble walking and even standing up. This type of neurological reaction to the virus is confusing, in that it is thought to be due to the body's response to the virus. When this ataxia is encountered we advise ample bedding, food and water close at hand, and symptomatic treatments which may include intravenous fluids. The v***a may not have much tone, the p***s is relaxed, or urine is retained in a bladder that is atonic (doesn't want to work). Other signs may be limb edema, vasculitis and neural ischemia (irritation to the brain and blood vessels) and ataxia problems with the front legs of the horse. A horse that is down and recumbent, or not able to walk at all, is not a good sign. Fortunately only a small percentage of the rhinopneumonitis cases are severe. The first 2 3 days of signs are usually the most severe. It may take 3 weeks to 2 months for some horses to recover from the neurological form of rhinopneumonitis, more commonly called equine herpes when it involves the nervous system. These horses need to be quarantined 30’ from other horses and if any horse has a re**al temperature of > 101.5 F a call to the veterinarian is indicated. With expensive horses there are some anti-viral herpes drugs available.
As with herpes in most animals, the virus is usually obtained within the first few years of life. The virus then remains dormant until the horse has undergone stress, such as seen with travel and pregnancy. Then the virus appears and causes its problems. There is no test to identify carrier animals. The treatment is supportive, using anti-inflammatory drugs, antioxidants and also antibiotics to prevent secondary bacterial infections, until a diagnosis is made. There are also immune stimulation type drugs which can help some patients. Acyclovir and its related anti-viral drugs can help only if the $100+/day therapy is started a few days before signs of infections; after signs of infection have started the antiviral drugs for herpes do not help. If there is an outbreak then a vaccination is indicated if your healthy horse has not had such a vaccine in 3-4 months; we do not routinely vaccinate sick animals. Although the influenza viruses can travel hundreds of feet in the air to infect other horses, the herpes virus travels less than 25' or so. A horse with a runny nose or a temperature over 102 F indicates it may have such an infection and this horse should not be given the vaccination, especially a modified live vaccine. We prefer killed vaccines for such an outbreak concern. With the virus lasting up to 6 weeks in the environment a 30 day quarantine for infected and/or incoming horse for biosecurity concerns is recommended. The vaccine can help reduce the severity of the signs of Rhinopneumonitis, even the neurological form, but not completely prevent it. Unless the horse is pregnant the vaccine only needs to be given every 6-12 months for the average horse in a stable situation, and less if on a pasture by itself.
We usually diagnose the problem by the history and the signs presented to us. Sometimes we may need to obtain blood samples 2 4 weeks apart to confirm the disease within a horse by comparing titers. A recent vaccination will interfere with the testing of the blood for the virus antibodies. Besides a necropsy, there is also a PCR test performed on a nasal discharge that can be used to diagnose the type 1 Rhino.
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