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|Equine Herpes Virus |
7 April 2003
British Equestrian Federation Press Release
For immediate release, Monday 7 April 2003
Equine Herpes Virus (EHV) paralytic disease
At present there are no official restrictions imposed by DEFRA as a result of the reported cases of EHV paralytic disease and there are no restrictions on the movement of horses.
The BEF?s Director of Sports Science and Medicine, John McEwen, advises individuals, yards and show organisers to continue their normal activities but to take sensible precautions regarding infected yards or yards in close proximity to an outbreak.
Isolation of infected yards is essential but fortunately the virus does not travel long distances through the air and infection is mainly by contact with infected horses.
It is wise to be vigilant in monitoring horse health to detect early cases of disease.
Information on the regions where infected cases have been identified can be found on the AHT web site www.aht.org.uk which is regularly updated.
Case Summary: 2nd April 2003
On 6th March, an 8 year old gelding on a point-to-point yard in Sussex began to show signs of ataxia (inco-ordination) progressing to recumbency and was euthanased. Brain and spinal cord tissues were submitted to the AHT where immunostaining techniques revealed evidence of EHV antigen, indicating EHV myeloencephalopathy (disease affecting brain and spinal cord).
No further cases have been reported from this yard or from other yards in Sussex.
Two Thoroughbred horses on a National Hunt racing yard in Gloucestershire began to show neurological signs within the same 24 period on 12-13 March. Both were euthanased due to rapid progression of signs from hindlimb ataxia, to paralysis and recumbency. Post mortem examination at the AHT revealed vascular lesions in the brain and spinal cord typical of EHV-1 myeloencephalopathy (list). Diagnosis was confirmed by immunoperoxidase staining for viral antigen. EHV-1 was isolated from a nasal swab from a third horse, which showed transient ataxia and from a heparinised blood sample from a fourth horse showing no clinical signs
No further cases have occurred on this yard or on other yards in Gloucestershire.
EHV neurological cases have been reported on two yards in Kent. There is no apparent connection between the two yards.
Mild cases on a small yard
On March 13, two horses on a small show-jumping yard in mid Kent developed signs of ataxia within the same 24 hour period. Interestingly, a mare that had arrived on the yard from Belgium 2 weeks previously was treated for lethargy and depression a few days before the neurological cases were observed. However, it is not clear whether this is significant or related to the neurological cases. Both ataxic horses were affected relatively mildly in that they did not become recumbent or paralysed and are now recovering. EHV has been isolated from heparinised blood samples from one of the ataxic horses and from the mare. Serological screening of the in-contact animals indicates that most have been infected although no more signs of disease have been observed.
Severe cases on a large yard
The second yard, a large livery yard in the area of Kent-Surrey-Greater London borders, has been much more severely affected. The first case was seen on 17 March. To date, seven horses have been euthanased on this yard due to development of severe neurological signs.
Signs have included hindlimb stiffness and reluctance to move progressing to ataxia, bladder paralysis (requiring catheterisation) or urine dribbling, reduced tail tone. Signs in severe cases have progressed further to include stiffness and ataxia in the front legs and recumbency. Signs of cranial nerve involvement have been seen in two cases.
Many cases have shown pyrexia (high temperature) a few days before the onset of neurological signs.
EHV infection has been confirmed by post-mortem examination and immunostaining, and EHV has been isolated from heparinised blood samples taken from unaffected horses on the yard.
New cases of neurological disease are still occurring on this premises. A neighbouring yard with direct contact (over the fence) but no signs of disease is being serologically screened to look for evidence of spread of infection.
We have not yet identified any connection between the four affected yards or evidence of spread to nearby yards.
Facts about EHV vaccination
There is no evidence to suggest that vaccination prevents neurological disease
The EHV vaccines available in the UK are licensed for use as an aid in the prevention of EHV respiratory disease and abortions. They have not been tested for prevention of neurological disease.
Vaccination should help to minimise signs and spread of herpesviral respiratory disease and to reduce the likelihood of abortion outbreaks, by reducing the amount of virus shed by an infected animal.
Vaccinated animals can still become infected or reactivate their own latent infection.
e.g. EHV abortions can still occur in vaccinated mares. There is as yet no evidence that vaccination can protect an individual animal from neurological disease.
Whether for protection against respiratory disease or abortion, there is probable little or no benefit in vaccinating a single horse against EHV if other horses on the premises are not vaccinated. It is important to treat the group as a whole. The best protection from disease is provided by reduction in virus shed by other horses in the group.
Vaccination in response to an outbreak may trigger disease.
Vaccination stimulates the production of antibodies in the blood. There is evidence from some studies that stimulation of antibody production in the presence of infectious virus may actually help to cause paralytic disease. We are worried that vaccinating a horse because there are cases of paralytic disease in close proximity could be a dangerous thing to do.
We advise against vaccination in the following situations:
if infection is suspected on the yard or has been already been diagnosed on the yard
Vaccination of nearby yards is unlikely to be of benefit and may be risky. Horses may be more susceptible to infection for a few days after vaccination. There may be a temporary reduction in immunity immediately following EHV vaccination, during which time the horse may be more susceptible to infection
If your horse is already vaccinated against herpes virus
We do not believe that horses that are already vaccinated against herpes virus are any more likely to develop the neurological disease. We are only concerned about risks to horses being vaccinated while the virus is active in the area. We are not aware of any outbreaks of paralytic disease in a group of horses fully vaccinated with this type of vaccine.
Vaccination in an attempt to protect against EHV neurological disease is a controversial issue. It is likely that there is no absolute right or wrong answer. We advise that you consult your own vet for advice on your particular situation. We are happy to speak to your vet to discuss the vaccination issue in cases where it is difficult to decide what to do.