It´s in the news every year: ‘Rhino outbreak in equine yard’. Rhino, or Rhinopneumonitis, is a very contagious viral infection which can cause symptoms of paralysis, respiratory problems or abortion. There are two strains, EHV-1 and EHV-4, which are both widely present in equine populations around the world. But what exactly is Rhinopneumonitis? How can outbreaks be prevented? And what to do when a horse becomes infected?

What is Rhinopneumonitis?

Rhinopneumonitis or Equine Herpes Virus (EHV) is a virus that manifests itself all over he world and which causes abortion, respiratory- or nerve symptoms. This virus is known to have various strains, with EHV-1 and EHV-4 being the most common.

EHV-1 can be responsible for a wave of abortions and is the only strain that can, in addition to respiratory symptoms, also cause nerve symptoms. EHV-4 on the other hand, can cause incidental abortions but mainly affects the respiratory system.
Herpes viruses are viruses that can be a serious burden for humans and equines. These are after all, viruses that stay in their hosts once they have been infected, without showing any symptoms. And in periods of reduced immunity, like at times of stress and illness they can trigger new diseases,… the same way as cold sores do in people. Horses that carry this virus are called carriers and are more or less a reservoir of Herpes virus. When rekindled they will again emit the virus.

How is the virus transmitted from horse to horse?

The infected particles end up in the environment via nasal discharge of an infected individual or by coughing. Virus particles are also transmitted into the environment by the amniotic fluid, amniotic sacs and the foetus itself after an abortion has taken place. The Equine Herpes virus can survive out in the open for roughly one month. The infected particles in the environment migrate via the air, equipment, clothing, etc. Other horses can inhale these infected particles and become infected too.

What are the symptoms?

Abortion by EHV usually materialises suddenly, without any prior symptoms. The time between the moment of infection and the actual abortion can vary between two weeks and a few months. This means that, in the case of EHV-1, many mares can be infected before anyone has even identified the disease. This situation will lead to a major outbreak of abortions. When dealing with the EHV-4 infection there will be less transmittance of the virus between individual horses so that miscarriages will be just incidental.
EHV produces inflammation of blood vessels in the uterus, causing the placenta to come loose. This will cut off the oxygen supply to the foetus in the uterus, who then dies of suffocation. The abortion usually occurs in the last three months of gestation, between 8 – 11 months. In most cases nothing seems to be wrong with the mare, except for the abortion, and the miscarried foetus is usually still fresh. When the foetus gets infected towards the end of the pregnancy it will be born alive. In such cases the foal is very weak or becomes seriously ill within two days. The tell-tale signs are a drowsy, feeble foal with a fever, respiratory problems, jaundice and sometimes nerve symptoms, with a life expectancy of no longer than three days.

When the respiratory system is affected there is a strong variation in clinical pictures. The symptoms are the worst in youngsters since they have had little exposure to viruses or bacteria and hence have built up little resistance. Along with youngsters, horses in training are also more vulnerable because of stress. It usually starts with nasal discharge, light coughing and reduced performances. Fever too, lost appetite and swollen legs can occur. Since the horse is temporarily in a weakened state it is more vulnerable to bacteria that live in the environment. When bacterial complications develop, the nasal discharge turns into pus. In most instances infected horses completely recover within a fortnight.

As stated before, the virus stays dormant in its host after the infection has taken its course. At times of reduced immunity such as during transport, re-herding, weaning, other diseases, overcrowding, stress,… the virus can be activated again. When reactivated the symptoms are milder with a shorter duration span, and sometimes there are no symptoms at all. But the virus is still being transmitted and dispersed across the environment.

In addition to abortion and respiratory issues the EHV-1 strain can also affect the nerve system, resulting in symptoms of paralysis. If this is the case the development of the disease is very acute. The virus causes damage to the blood vessels in the brain and spinal cord, resulting in damage to the nerve cells. This manifests itself in ataxia of the hindquarters, paralysis of tail and bladder, even progressing to full paralysis. As with respiratory disorders, swelling of legs and scrotum can also occur.


How can infection with Rhinopneumonitis be identified?

Diagnosing Rhinopneumonitis can only be done in a laboratory. When clinical symptoms suggest an EHV infection it is necessary to take nasal swabs, blood samples from the mare, swabs of the aborted foetus and sacs, and send these off to the laboratory. In case of a miscarriage it´s therefore always important to seek advice from your vet so that the required swabs can be taken.

What is the treatment of Rhinopneumonitis? How to prevent infections?

If the horse only shows signs of respiratory symptoms, anti-inflammatories can be administered. These keep the fever down and stimulate appetite, which helps to keep possible complications at bay. After a bacterial infection administering antibiotics is an option, but as we´re dealing with a viral infection antibiotics have no effect in the early stages of the disease.

When the horse shows nerve symptoms, cortisone can be effective, but most important is to take supportive measures to help the horse. By this we mean nutritional support, but also providing the horse with a hoist support in the shape of a girth around its belly, providing a non-slip surface and if necessary, catheterisation of the bladder. Unfortunately, prognosis for the EHV-1 variant with nerve symptoms is often a sad one.

In case of an abortion there is no need for treatment of the mare, but it is absolutely essential to take measures to prevent further spreading of the virus. Removal of foetus and amniotic sacs is key, as well as thorough cleaning and disinfecting of the spot where the abortion happened. Because the foetus, amniotic fluid- and sacs are a huge source of infection for other animals! As the Herpes virus can survive in the environment for a period of four weeks, it is advisable to seal this area off for other horses. Personal hygiene is also important because the virus can be transmitted through clothing, hands or other equipment.

To avoid abortion by Rhinopneumonitis, prevention is key. Therefore horses should be vaccinated against Rhinopneumonitis. Vaccination will not prevent horses from getting infected, but it does reduce the symptoms and chances of spreading. For this reason the advice is to have all horses vaccinated against Rhinopneumonitis on a twice-yearly basis. All horses does not just refer to pregnant mares, but includes sport horses, foals, young stock in foal-raising yards,… any horses living in the yard. Additionally, pregnant mares need to be given boosters three times during pregnancy, at 5, 7 and 9 months after insemination. (Zangersheide has devised a disk, a tool to provide clarification with regard to the necessary vaccination programme of pregnant mares. If you like, you can order this disk at any time.)

Best practice is to group pregnant mares together, if possible separate them from other horses. Newly-arrived horses have to be isolated from other horses for a period of three weeks. Along with this, stress should be avoided as much as possible to prevent reactivation of the virus in carriers. To improve the overall immunity of horses a stable feeding regime is important, as well as a good de-worming scheme, steady management and Influenza vaccinations. 

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