Parts 1 and 2 discussed EHV virus in some detail and the causes, spread and prevention of virus abortion in mares in mares.
What is the paralytic or neurological form of equine herpes virus?
In addition to causing outbreaks of abortion in mares (particularly non vaccinated mares) and respiratory infections, Equine Herpes Virus can occasionally cause paralysis. While there have been some outbreaks of the disease in Ireland, it is not a very commonly encountered problem here. What causes herpes paralysis in horses?
Equine Herpes Virus Type 1 and EHV Type 4 can cause the paralytic or neurological form of the disease. The paralytic signs are seen with both the neurological and ‘non-neurological’ strains of the Equine Herpes Virus, i.e. the differentiation is not clear cut. Therefore control measures should be adopted consistently irrespective of the strain of EHV-1 involved. What are the signs?
The onset of paralysis can be quite sudden either with or without prior clinical signs of respiratory disease caused by herpes virus. This usually occurs in the second week following infection. There may be a mild in-coordination of the affected horse’s hind limbs similar to signs shown by a “wobbler” or there may be a total paralysis. In the more severe cases, there may be a complete paralysis where the horse is unable to stand. These horses can appear quite alert etc but they are unable to stand. In some cases, the nerves supplying the bladder may become paralysed and the horse tends to leak urine. This is especially noticeable in some mares. Does it occur in all types of horses?
Yes. While it is most commonly seen in broodmares it can also occur in racehorses, sport horses, etc. It is usually seen in animals over five years of age. Is the disease seasonal?
The autumn, winter and spring are the higher risk periods when animals are more likely to be stabled and when UV light/sunlight levels are low. What is the usual treatment?
Since the disease is caused by a virus, antibiotics are of little benefit. The treating veterinary surgeon will recommend supportive treatment such as special vitamins to help regeneration of the nerves affected by the virus. Anti-inflammatories are prescribed in some cases. How is it diagnosed?
Blood samples and nasopharyngeal swabs are taken by the treating veterinary surgeon, for laboratory testing. Where an affected horse dies or is euthanised, post mortem examination will confirm diagnosis. Can it be prevented?
As with viral abortion, vaccination can help prevent the paralytic or neurological strain of Herpes. Is the paralytic form of EHV notifiable?
No. However many believe that the paralytic form of EHV should be a notifiable disease. Historically there have been occasions where mare owners sent their mares to studs without knowing that the stud had an outbreak of EHV paralysis, only to return home and find their mare paralysed after a few weeks. Does this vaccination also prevent the respiratory form of the disease?
Yes it helps to prevent the respiratory form but this will depend on the causal strain of the virus. The respiratory form can cause quite a recurring problem in performing horses. The symptoms resemble those of a recurring ‘flu. It is treated in much the same way as ‘flu with antibiotics given to treat the secondary infection. It recurs at times when the horse is stressed and it reactivates, causing major problems in a training programme in a yard. Is EHV vaccine compulsory in training yards or for racing or showjumping purposes?
While it is not compulsory, many trainers vaccinate their horses with herpes (EHV0 vaccine) on a regular basis to help to prevent the respiratory form of the EHV disease. The Turf Club and FEI compulsory vaccination requirements are specifically for Equine Influenza.