Hendra: why not just go ahead and vaccinate? - web series by holistic equine veterinarian, Dr Christine King

An important risk factor that is unique to the Hendra virus (HeV) vaccine is the fact that many equine vets in Queensland and New South Wales won’t come out to see a sick horse if the horse isn’t "currently" vaccinated against HeV according to the Hendra vaccination registry owned and managed by Zoetis.

So, there is risk in not being able to find a vet when you urgently need one if you decide not to vaccinate or not to continue vaccinating against HeV.

There are a couple of different reasons why vets make this decision. One is for their own safety and that of their staff, families, and own horses. Another is to avoid legal trouble: some vets have had to pay huge fines for not taking what the government considered "appropriate" steps to protect human health. For whatever reason, this decision is not made lightly. No responsible vet wants to leave an animal in need of medical attention.

There are a few vets who will treat unvaccinated horses or horses whose vaccination status is overdue, lapsed, or unknown. Others will see the horse but, depending on the circumstances, may insist on running a HeV exclusion test before proceeding with any diagnostics or treatment. It very much depends on the reason for the visit.

For example, wounds are treated much differently than colic, because a wound is not a sign of HeV infection whereas a few horses with HeV infection have shown signs of pain that may be mistaken for colic.

This particular risk (not being able to get a vet to see your horse in an emergency) is serious enough to warrant inclusion in your deliberations. Is it enough on its own to tip the scales in favour of vaccinating? That may depend on where you live and what veterinary resources you have available.

One thing I suggest you do before making this decision is to call around to the equine vets who service your area and ask about their Hendra policy. Then compile a list of vets who will come out on emergency if you decide not to vaccinate or not to continue vaccinating against HeV. To be thorough, also call the equine hospitals with surgical facilities in your area and ask about their Hendra policy. Make note of those who will accept, at least on a case-by-case basis, horses who are not "currently" vaccinated against HeV according to Zoetis and its Hendra vaccination registry.

Incidentally, some equestrian event organisers also require proof of "current" HeV vaccination in order for the horse to enter the grounds and participate. It's up to you whether to support such events.

Proof of immunity instead

I have been encouraging vets, farm/barn managers, and event organisers to start accepting proof of immunity as an alternative to proof of vaccination.

It would be great if annual HeV antibody testing became commonplace and the standard of care for horses in QLD and NSW. Then there would be no need to deny service or entry to any horse with proof of immunity to HeV.

Currently, the HeV ELISA costs about the same as a dose of the HeV vaccine, although this test just provides a positive/negative result. (It simply tests for presence/absence of HeV antibodies in the horse's blood.)

The HeV serum or virus neutralisation (SN or VN) test is much more expensive but it provides a numerical result, or titre.

Armed with the results of either test, horse owners can make better vaccination and other management decisions, and equine vets concerned about treating horses who are not fully vaccinated according to Zoetis can have more confidence that they are at low risk of contracting or spreading HeV from these horses.

UPDATE 04 July 2024

An alternative to costly titre testing, called a microsphere-based immunoassay (MIA), has recently been validated against the gold-standard VNT. In a study involving Thoroughbred mares and foals in the Hunter Valley (NSW), the MIA was shown to be a useful proxy for titre testing. Once it's commercially available, it should be much cheaper than titre testing because it does not require the use of live virus (as the VNT does). The results are reported as median fluorescence intensity (MFI), an MFI of 4,000 being approximately equivalent to a VNT of 32, and therefore expected to be protective against HeV infection.

Read on...

Last updated 04 July 2024.

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