12/01/2020
‘Equine Herpes Outbreak - The Facts’
Reposted from John Dunsford Equine Vets
We have confirmed cases of Neurological Equine herpes virus (EHV-1) infections locally in Hampshire causing untreatable paralysis and necessitating euthanasia.
The Equine herpes viruses are endemic in the UK. This means that like cold viruses or the glandular fever virus they are about all the time, and there is no current likelihood that the UK will be free of them.
Equine herpes viruses are named EHV-1, EHV-2, EHV-3 and EHV-4.
Within each of these named groups there are a number of different strains, in the same way that influenza has multiple strains. Some strains are quite benign and some are quite nasty.
EHV-2 is a common mild virus which most horses have had at sometime.
EHV-3 is ge***al herpes in horses and is only spread sexually.
EHV-4 is a respiratory virus which is passed around between horses and can be quite debilitating, especially in young animals. It is spread by coughs, sneezes and by ‘not using a tissue’ type things like human viruses are. Paralysis or miscarriage can only very occasionally follow an EHV-4 infection.
EHV-1 is similar to EHV-4, but has a higher incidence of miscarriage and paralysis associated with it, but only with certain strains. EHV-1 has groups of strains named neuropathic (paralytic) and non-neuropathic, but variants of both strains can cause paralysis or miscarriage. There are multiple strains within each of these groups, some benign and some nasty.
Most horses have had an EHV-1 infection at some time with a benign strain, often without the owners even realising it. We know this as after infection horses have anti-EHV-1 antibodies, which we can test for.
If a horse develops paralysis after a paralytic strain EHV-1 infection it is due to the virus misleading the horse’s own immune system into attacking blood vessels around nerves. Not all horses will react in this way though. Probably less than half, and those horses who do not attack their own blood vessels will recover without paralytic symptoms.
EHV-1 in younger animals often shows itself as a respiratory infection with a temperature. These under-fives are much less likely to become paralysed even with a nasty strain of the virus. Older horses are more likely to become paralysed and less likely to show other symptoms. Occasionally the paralysis is the first symptom seen.
Herpes is a virus so antibiotics are of no use. And there is no specific anti-viral drug or treatment.
Like other herpes viruses, including the human cold sore virus, and the chickenpox/shingles herpes virus, the EHV Equine herpes viruses can lie dormant after the patient recovers, and reoccur at a later date. This is called a Latent infection. As most horses have had EHV-1 there are a great number of latent carriers among all of our horses.
EHV-1 is not new or strange. We have had it in this country for ever. It is not ‘notifiable’ meaning that it is not subject to any government restrictions or action. As with the Influenza it is down to us, the Equine community to be responsible and sensible. The Horse Race Betting Levy Board publish a Code of Practice in relation to EHV in the racing industry. This Code of course also makes sense for all the rest of us, and includes advice about herpes miscarriages. If a mare miscarries due to EHV-1 it is hard to contain the virus. Unexpected miscarriages should be handled with great suspicion and treated as potentially highly infectious.
There is a vaccine available called Equip EHV 1-4.
Equip EHV 1-4 is licenced to reduce clinical signs of the respiratory forms of EHV-1 and EHV-4. It is also licenced to reduce the risk of EHV-1 miscarriage in pregnant mares.
The role of the vaccine in paralytic strains of EHV-1 is perhaps more complicated as vaccines work on the horse’s immune system, which is both a complicated thing, and also the thing which will cause the paralysis if that does occur. In general vaccination is a good thing which has saved countless lives of all species, including our own. Modern scepticism about vaccination flies in the face of the evidence which shows its huge and overwhelming life-saving benefits.
With EHV-1, vaccination of whole yards makes good sense as it prevents the spread of the virus from horse to horse and reduces the chances of more horses becoming exposed to the virus. For individual horses living alone, or where no horses arrive or leave home there is probably less reason to vaccinate as they are at low risk of infection and it may be better just to observe biosecurity.
Where there have been diagnosed cases, possible in- contact horses should not be vaccinated as vaccination will raise their EHV-1 antibodies, and it will not then be possible to tell if the horse has actually contracted the virus.
Biosecurity, as with Influenza, means keeping oneself to oneself and not travelling about and not letting new horses mix. The virus is not reckoned to travel further than fifty metres in the air. Biosecurity is also understanding that the virus can be spread on hands and clothing, buckets and other non-living things. EHV-1 can last on in-contact things and in the environment for up to a month.
Incubation can be up to two weeks. Three weeks is considered to be safely out of danger.
While young animals may be snotty, older horses may not show many symptoms of going down with the virus. Monitor your horse’s temperature and look out for lack of appetite or anything unusual. We hope that this current Hampshire outbreak will soon be over, with sensible behaviour from all of us. Obviously there is the question of where the first horse brought the infection in from, and as such the infection may yet be seen elsewhere in the country. Although this horse may not have shown symptoms itself, and the animal may not actually be known.
