The most important ways to prevent EHV infection are good management of breeding stock, good hygiene at all times, especially during breeding activities, and regular vaccination of all equine animals as part of a good biosecurity protocol.
Management of breeding stock
All horses and ponies, including foals, can be a source of EHV. Breeding stock should, therefore, be managed in ways that will minimise the risk of spread of infection between horses:
• Pregnant mares should be kept separate from all other stock, e.g. young stock (weaned foals, yearlings and horses out of training), non-pregnant horses of all types and ponies;
• Pregnant mares should spend as much time as possible in small groups with similar due dates, out at pasture and should not be stabled, especially in shared air space stabling, unless essential. Larger mare groups in close proximity, particularly in shared airspace stabling, increase the risk of transmission of infection to more mares in the event that there is EHV abortion and/or respiratory EHV infection, potentially overwhelming vaccinial immunity. EHV does not travel long distances as an aerosol so close contact between horses should be minimised by sensible management;
• Suddenly stabling pregnant mares who have been out at pasture may precipitate an EHV abortion, even in a vaccinated herd;
• Where possible, mares should foal at home and go to the stallion with a healthy foal at foot;
• If foaling at home is not possible, pregnant mares should go to the stallion or boarding stud at least 28 days before foaling is due. These mares should be placed in quarantine for 2 weeks and then isolated in small groups with other healthy mares who are at a similar stage of pregnancy. The groups should be as small as possible in order to minimise transmission of infection in the event that EHV abortion and/or EHV respiratory infection occur;
• Mares arriving from sales yards or from overseas are particular risks as they are more likely to have recently mixed with other animals of unknown EHV infectious and vaccinal status and should be grouped and isolated away from other pregnant mares;
• Isolated groups and individual pregnant mares should be separated as far as possible from weaned foals, yearlings, horses out of training and all other types of non-pregnant horses and ponies. On stud farms, fillies out of training are a particular risk to pregnant mares but the same is true for all young horses;
• Pregnant mares should not travel with other horses, particularly mares that have aborted recently;
• Any foster mare introduced to the premises should be isolated, particularly from pregnant mares, until it has been proved that EHV did not cause her own foal’s death;
• Stallions should wherever possible be housed in premises separate to the mare operations and should be attended by separate dedicated staff, adopting strict biosecurity measures. If it is not possible to have dedicated stallion staff then it is even more important that strict biosecurity measures are adopted to minimise indirect transmission of infection between different horse groups on the stud.
All horses can be potential sources of infection, and the virus may survive in the environment for up to one month, depending on conditions, following excretion by a horse. Good hygiene is therefore essential:
• EHV is destroyed readily by heat and contact with virucidal disinfectants. Stables, equipment and vehicles for horse transport should therefore be cleaned, steam cleaned and then disinfected with an approved disinfectant regularly as a matter of routine and certainly between occupants. Wherever possible virucidal disinfectant should be allowed to dry naturally in contact with surfaces in order to maximise the chance of destroying the virus;
• Staff should be made aware of the risks of indirect (by people) transmission of EHV and hand washing/alcohol sprays should be provided and used, whenever possible, for the use of staff when moving between horses;
• Wherever possible, separate staff should deal with each group of mares. If this is not possible, pregnant mares should be handled first each day in order to avoid the possibility of indirect transmission of EHV from other horses and strict biosecurity measures, including hand washing/alcohol sprays, separate tack, change of clothes etc. are even more important;
• Separate equipment and clean water should be used for each horse or group of horses;
• Foaling staff should wear single use disposable coveralls and a new pair of disposable gloves each time they foal a mare and then must dispose of them safely afterwards.
Specific vaccination of all horses in a herd will raise the level of protection within the population against EHV. Although it will not prevent individual animals from aborting due to EHV infection, experience suggests that vaccination is advantageous in reducing the risk of multiple abortions (so-called ‘abortion storms’) on stud farms. Experience shows that ‘abortion storms’ are much less likely to occur in properly vaccinated pregnant mare populations and specific vaccination is highly recommended. However, because of the nature of herpes viruses and their ability to cause latent (carrier) infections, vaccination will not provide total protection, so good management and biosecurity remain paramount.
It is recommended that a herpesvirus vaccine, licensed for use as an aid in the prevention of both abortion and respiratory disease caused by EHV-1 and/or EHV-4, is used for all horses on stud farms.
It is recommended that all horses resident on a stud farm are fully vaccinated with a primary course followed by regular 6-monthly boosters. Pregnant mares should be additionally booster vaccinated at 5, 7 and 9 months of gestation.
Consult your veterinary surgeon. See Appendix 8 for vaccine details.