The common cold, which affects almost all horses and almost certainly affects almost 100% of young competition horses, has been a problem for centuries. A condition was reported in horses in 1751, which in retrospect almost certainly was due to infection with a Herpes virus.

The Common Cold vs. the 'Flu'

It must be remembered that even though many horse owners and trainers refer to their horse’s having the “FLU” there is no influenza virus present in Australia. This is an extremely infectious debilitating disease which has by stringent quarantine control been kept out of Australia. Its introduction in this country would cause millions of dollars loss in cancelled horse sporting events until vaccination programs and horses immunity placed the disease under control, however all performance horses would require lifelong vaccination to control the debilitating effects of this disease.

The most prevalent respiratory disease in horses in Australia is “THE VIRUS” and while EHVl& 4 are not the only respiratory viruses affecting horses they are the most common and the most economically disruptive to the Australian horse industry.

Equine Herpes Virus (EHV)

It has been found by Dr Michael Studdert, of the Melbourne Veterinary School that there are two distinct types of EHV, which are now known as EHVl and EHV4. Both of which are capable of causing respiratory infections and abortions. EHVI is more commonly associated with abortion and in horses that are unlucky to develop neurological signs (hind leg paralysis), while EHV4 is more likely to be related to respiratory disease.

Factors that have made the control of EHV difficult

  • The virus is spread by direct contact and by aerosol (sneezing coughing etc)
  • Spreads rapidly and virus multiplies rapidly
  • Recovered animals often remain carriers
  • Short immunity
  • Very high infection rate
  • Where horses have outside contact re-exposure and so reinfection is common

Up to 85 % of all foals can become infected in the first year of life due to the cyclical nature of the disease and lack of strong natural immunity, and can be re infected easily. Carriers redevelop the disease if stressed.

Respiratory signs

  • Foals and yearlings may be first noticed to be dull with a watery eye and nose discharge that soon becomes muco-purulent.
  • Appetite is poor and there may be swelling of the glands under the jaw.
  • Coughing often follows.
  • Secondary bacterial infections often follow leading to sore and swollen throats and pneumonia. There may be a serious check in the foal or yearling’s growth rate.
  • Please note – always be aware that outbreaks of strangles can start with much the same clinical appearance.

Two to three year old horses will have a dramatic loss of performance and if continued in racing may develop serious side problems such as respiratory disease leading to pneumonia, pleurisy, and wind problems such as roaring. Displaced soft palate can occur as a complication. Heart muscle damage has been reported in horses stressed by work.


Pregnant mares in the last trimester of their pregnancy may abort anywhere between 9 - 90 days after being infected. They may not show any warning signs of impending abortion; this is different to placental disease where the mare may show udder development days before aborting. The newborn foals of infected mares may be born with severe respiratory disease and often die within 24 - 72 hours of birth. It has been recorded in the Hunter Valley that foals have died up to 14 days after foaling with intractable pneumonia due to Herpes Virus.

Nervous signs

EHV1, most commonly a staggery gait leading to severe posterior paralysis and the horse becoming unable to stand. Horses so affected don’t always have preliminary signs of respiratory disease or abortion before the development of neurological signs. It is fortunately quite rare in Australia. While horses can recover from this form of the disease, a fairly large percentage don’t get up and have to be destroyed.

Protection with Duvaxyn EHV1,4 Vaccine

Isolates from Australian horses have been purified for vaccine production at University of Melbourne where a new state of the art vaccine production was implemented and a new vaccine produced. This has been extensively tested both in Australia and overseas to ensure its safety and potency.

It is currently registered for use in the control of respiratory EHVI AND EHV4 in Europe and also against abortion more recently in the UK. The vaccine is registered for use in Australia for primary and booster vaccinations of healthy, susceptible, immunocompetent horses and ponies against respiratory diseases caused by EHVI and EHV4.

The vaccine is recommended for use in healthy horses and ponies from 5 months of age

Vaccine recommendations

  • Where foals have received adequate colostral antibodies the earliest and best age is 5 - 6 months
  • Foals with low or no colostral antibody should be initially vaccinated at 3 months of age. This is boosted at 5 – 6 months and again 4 - 6 weeks later
  • Mares should be vaccinated three times at 5, 7, and 9 months
  • All performance horses and all other horses should receive booster doses every 6 months.
  • Some horses will show nasal and ocular discharges and many will show swelling of the glands under the throat. Some may show transient temperature elevation.
  • Vaccination is made by deep intramuscular injection
  • You should consult your Veterinarian about the correct programmes for your horses
  • The vaccination does not prevent clinical infection occurring, but will significantly reduce the severity of the disease and significantly reduce the subsequent transmission of virus to other in contact horses.


  • The vaccine can cause localised and/or generalised reactions after injection. These are usually of short duration.
  • Severe hypersensitivity is rare but is to be regarded seriously and treated immediately by your veterinarian.
  • Avoid stress at the time of vaccination
  • Opened vials are discarded as both contamination and degradation of virus occurs, Immunosuppressive drugs, such as cortisone can interfere with vaccination and horses under such treatment should be not vaccinated until an interval of 4 weeks from the last treatment has elapsed.

EHV respiratory disease is an extremely complex disease condition. Subclinical cases can excrete virus so these horses have the potential to upset the normal vaccination program.

Minimise the spread of disease, keep vaccinations up to date, isolate any horses that may have or be incubating the disease to reduce the overall infection rate and reduce the potential challenge to other horses.