animal health consulting

Hendra: why not just go ahead and vaccinate?

Christine King  BVSc, MANZCVS (equine), MVetClinStud

Table of Contents

Summary (key points)

Introduction

Risks

   the virus

   the 'vector' (flying foxes)

   the vaccine

   vaccination status

Benefits

   the vaccine

   experimental study

   vaccine field study

   vaccination status

HeV antibody testing

Letter to the Editor (AVJ)

Final thoughts



HeV antibody testing


The CSIRO Australian Centre for Disease Preparedness (ACDP, formerly the Australian Animal Health Laboratory) in Geelong, Victoria offers the following tests on equine serum:


1. Hendra virus ELISA (enzyme-linked immunosorbent assay)


This test simply provides a positive/negative/inconclusive result; it does not give us a numerical value. However, in the 2018 study of diagnostic methods I've mentioned a few times, the breakpoint between "positive" and "inconclusive" was a virus neutralisation titre of 2.4. So, any horse with a titre of 2.4 or higher is likely to have a positive ELISA.


Although it does not provide a numerical result, this test is the less expensive of the two, and a positive result indicates the presence of HeV-specific, virus-neutralising antibodies. From it, we can also infer immunological memory. (Remember that antibody production is only one component of the immune response.)


If the result is positive, vaccination/booster may not be necessary at that time. If the result is negative, vaccination/booster may be considered, depending on the individual circumstances.


The current laboratory fee for this test is $111.10 per horse (including GST).


2. Hendra virus VNT (virus neutralisation test), or HeV titre


This test is the 'gold standard' as it provides a numerical value. Based on the available research in horses, a titre of 16–32 is considered protective against HeV, although in real-world situations of HeV exposure the threshold is likely to be much lower (titre of 4 or less), as antibody production is rapidly increased in the face of challenge in horses who have prior experience with HeV, whether through natural exposure or vaccination (even a single dose).


If the titre is at least 32, vaccination/booster may not be necessary at that time. If the titre is 16 or lower, vaccination/booster may be considered, depending on the individual circumstances.


The current laboratory fee for this test is $367.40 per horse (including GST).


Note that both of these tests require blood collection and submission by a registered veterinarian, so veterinary fees and shipping costs are additional.


***


Below is a link to a PowerPoint slideshow I made on how to use HeV antibody tests as proof of immunity, in place of proof of vaccination:


Hendra antibody tests —guidelines for vets, farm managers, and event organisers



Read on...


© Christine M. King, 2021, 2022. All rights reserved.

Last updated 30 May 2022.


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