Dealing with the Equine Herpes Virus
A current outbreak of a serious and life-threatening equine disease has struck Europe and is migrating to the United States. Equine Herpes Virus (also known as EHV-1) causes a multitude of clinical signs which range in severity. It most often affects the respiratory system of horses, but can also be responsible for abortions in mares and the most severe clinical signs are neurologic.
The neurologic form is call Equine Herpes Myeloencephalopathy. Horses are usually exposed to the virus at a young age with little to no consequences, as the virus is ubiquitous in the environment and found in most horses all over the world. When the virus causes respiratory infection, it is called rhinopneumonitis.
It is currently unknown what triggers the virus to cause the severe neurologic form in certain horses. The virus is responsible for damaging blood vessels in the brain and spinal cord leading to a variation in severity of neurological disease. EHV-1 is easily spread between horses that comingle in pasture or who come into contact with a horse that is shedding virus at shows or trail rides.
EHV-1 has an incubation period of 2-10 days and respiratory secretions can shed virus for up to 10-14 days. Certain horses will harbor a latent infection and be able to shed virus intermittently without any clinical signs. The outcome of infection in each animal seems to be dictated by how stressed they are during early infection and how much rest they can actually achieve. The virus is quite stable in the environment and without proper disinfection can live for several weeks. It is susceptible to many over the counter disinfectants such as, diluted bleach, alcohol and chlorohexidine.
Clinical signs often start with the horse becoming lethargic leading to nasal discharge that starts out clear but often turns thick and yellow, accompanying a low-grade fever around 101.5. The virus may then cause weakness in the hindquarters, incoordination, dog sitting, dribbling urine and ultimately recumbency. If your horse exhibits any of these signs you should contact your veterinarian who will perform nasal swabs and other diagnostics to achieve a diagnosis and start supportive therapies.
As a horse owner, it is vital to make sure your horse is well vaccinated for EHV-1. It is important to understand that EHV-1 or rhinopneumonitis has many established vaccines, but that the neurological form currently does not. It is thought that the EHV-1 vaccine might allow for some cross-protection, but it is not guaranteed.
A vaccinated horse will have much less viral shedding helping protect other horses it comes into contact with. The vaccine is recommended every six months for boarded horses and for animals that attend shows and travel frequently. It is also important for horse owners to thoroughly disinfect stalls at shows and be sure to not allow for noseto-nose contact or any sharing of feed or water buckets.