Rhino - An Unsolved Equine Mystery

“Rhino”  is a term used in the horse world to describe diseases caused by a virus in the equine herpesvirus family. The term “rhino” comes from the Latin word for nose, because one of the signs of infection is a runny nose. Unfortunately, a runny nose is one of the least worrisome problems caused by this mysterious virus.

Equine herpesvirus causes three types of disease. Most commonly, it affects the airways and causes fever, loss of appetite, a runny nose and cough. These symptoms are very similar to those caused by equine influenza virus. Most horses recover in two weeks, but the cough may persist for up to three months. Horses with a cough must be rested to allow the lungs to heal. Damage caused by the virus can depress the lungs immunity and result in secondary bacterial infections that require veterinary attention and treatment with antibiotics. 

Rarely, equine herpesvirus travels to the brain and nervous system and causes severe, life threatening illness. Signs include loss of balance and coordination and inability to urinate. Aggressive veterinary care will  decrease inflammation in the brain and spinal cord,  despite this, many horses fail to recover.  Why equine herpesvirus travels to the nervous system in some cases and not others remains a mystery.

In mares, equine herpesvirus can travel from the airways to infect the uterus after the fifth month of pregnancy. This causes abortion or premature delivery of a weak foal that will not live. Exposure of other pregnant mares to the placenta, dead foal or uterine fluid from infected mares can cause outbreaks of abortion.

Protecting our horses from equine herpesvirus is a difficult task for two main reasons. Firstly, many horses carry herpesvirus in their bodies for long periods without any signs. In times of stress, the herpesvirus multiplies and is spread in the nasal secretions to other horses.  To date, we do not have a test to tell us which horses carry herpesvirus, nor do we have a way to eliminate the virus from their bodies. Secondly, the vaccines we have available today against equine herpesvirus have not been proven to be highly protective.

Currently, a vaccine against herpesvirus is included with influenza vaccine in products such as Calvenza. However, unlike the influenza vaccine, the equine herpesvirus vaccine is not highly effective. Full vaccination with Calvenza have been shown to decrease the severity of respiratory disease for three weeks after vaccination. Also, these horses shed less virus to others. The vaccines Pneumobort K and Prodigy are given to pregnant mares to prevent abortion caused by equine herpes virus. These vaccines have been shown to reduce the risk of abortion, but do not completely eliminate it and must be given at five, seven and nine months of pregnancy. Careful management of pregnant mares with or without vaccination is the best method of reducing the risk of  abortion caused be equine herpesvirus. None of the vaccines against equine herpes virus have been shown to prevent the rare nervous system form of disease.

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