Doing things “right” when you get a Herpes virus outbreak is still stressful but it works.

What is “right”?  The New Zealand equine industry has adopted a Code for the control of Equine Contagious Diseases. In essence, it is isolate, separate, communicate, disinfect, investigate and test for freedom.

Last month New Zealand had its second reported emergence of equine herpes myeloencephalopathy.  The property concerned followed the Code to the letter and have just updated the NZEHA that they have received negative 28 day PCR results on all the animals who were contacts with the affected case.  It has been a stressful time involving a mammoth amount of work on  this property and the NZEHA applauds their commitment to transparency, disease management and biosecurity.

Just to clarify, Equine herpes virus -1 (EHV1) is present across all horse populations world wide including New Zealand.  Equine herpes myeloencephalopathy (EHM) is one of the clinical presentations seen when the virus has overcome an animals immune system to produce signs of illness.  Other illnesses seen due to EHV1` are respiratory in nature or late term abortion. Most horses become infected with EHV 1 as youngsters with few symptoms.  Rather than clearing the virus, horses, like people, often harbour the herpes organism in their nervous tissue. When immunity wanes, usually later in life, it can reactivate causing a varied range of symptoms and affected horses produce a lot of virus which is available to infect naïve in-contact animals.

Early aggressive intervention can prevent spread of the virus to other horses.  In the latest case the property has had no further clinical cases.  They immediately separated horses and people into contact and non-contact groups and observed all horses intensively looking for any clinical changes including temperature spikes. They PCR tested all the contact horses every week taking nasal swabs, and you can imagine what fun that was! 

Because the property normally needs to move a lot of horses in and out they have regularly repeated nasal swabs and are undertaking a lot of serological testing to ensure there is no silent spread before they considered opening their gates again to resume normal activity.  They have continued to keep the horses that were in-contact with the case separate and have surpassed the 28 day period since the last clinical case, thus have opened up the unaffected side of their business and are beginning to relax their protocols. 

Unfortunately New Zealand horse owners have to live with the uncertainty that arises from having EHV1 circulating across the equine population. But great horsemanship and property management can limit the size of outbreaks. Vaccines do enhance the horses immunity but it appears that immunity wanes relatively quickly and horses with waning immunity if exposed to overwhelming amounts of the virus remain at risk of disease. The NZEHA recommends that vaccination is always supported by excellent disease management practices and are delighted to see these becoming the norm.

New Zealand equine vaccination guidelines are currently being updated but the recommendations for protection against EHV1 will largely remain unchanged.