CASE NOTES
HENDRA VIRUS DEVELOPMENTS 2012
Therese Wright, Biosecurity NSW
Posted Flock & Herd April 2013
Introduction
This article aims to provide a summary of developments relating to Hendra virus in 2012.
SUMMARY FIELD CASES 2012
In 2012, 121 horses died of Hendra virus in 9 incidents. All these incidents2 were confined to Queensland and all occurred on properties north of Gladstone, as shown in Figure 1 below.
Figure 1: Map showing locations of Hendra incidents
In all cases, except the July Rockhampton case, only one horse was infected. No other in contact animal was infected.
Early winter to spring continued to be the highest risk period for Hendra virus incidents, with five occurring in May to July and three in September to November. Data on the incidents in 2012 is summarised in Table one below.
| Hendra virus incidents 2012 | ||
|---|---|---|
| Location | No. horses infected | Date incident |
| Townsville region, Queensland | 1 | January 2012 |
| Rockhampton, Queensland | 1 | May 2012 |
| Ingham, Queensland | 1 | May 2012 |
| Mackay, Queensland | 1 | June 2012 |
| Rockhampton, Queensland | 3 | July 2012 |
| Cairns, Queensland | 1 | July 2012 |
| Port Douglas, Queensland | 1 | September 2012 |
| Ingham, Queensland | 1 | October 2012 |
| Ingham, Queensland | 1 | November 2012 |
Table 1: Summary of Hendra incidents in 2012
ISSUES WITH INTERPRETATION OF TEST RESULTS FROM 'IN CONTACT' ANIMALS
Hendra virus testing of 'in contact' animals on infected premises in Queensland in 2012 highlighted potential issues with the interpretation of laboratory tests. Two 'in contact' horses one infected property at each tested 'positive' on a single PCR test result on one swab and a dog on another property returned a single 'positive' PCR test result from a rectal swab. However all other samples from these animals including subsequent testing from a modified sampling protocol were negative.
All aspects of these cases were reviewed by an expert panel made up of an immunologist, senior veterinarians, and animal pathologists from across Australia.
The panel agreed that the animals were not infected and did not pose any risk. The expert panel concluded that since both horses did not demonstrate corroborating positive PCR results (either from other sample types or sample times); any signs of clinical disease; or seroconversion (as evidenced by negative ELISA and Serum Neutralisation Tests results), there was no evidence of systemic infection with Hendra virus. A number of plausible explanations potentially explained the initial positive detection of viable or non-viable Hendra virus genetic material by PCR including local Hendra virus replication in only the horses' nose or Hendra virus being present in the dog's gut lumen (after ingestion and gut transit) or viral material was present on the skin on the dog (e.g. horse faeces or other matter).
These incidents highlighted the need to:
- interpret any individual laboratory result in the light of both clinical information and additional laboratory test results, and
- collect dual sample sets with one set to be held by the state laboratory and available for retesting if required.
RELEASE OF THE HENDRA VIRUS VACCINE
A Hendra virus vaccine for horses produced by Pfizer Animal Health was released on Thursday 1 November 2012. The vaccine is available under a special HYPERLINK "http://permits.apvma.gov.au/PER13510.PDF" Minor Use Permit issued by the Australian Pesticides and Veterinary Medicines Authority (APVMA). It may only be ordered and administered by accredited veterinarians who have completed an online training module managed by Pfizer Animal Health.
Data is currently being collected on the safety of the vaccine including in foals and breeding animals and on the duration of immunity. To reach full registration, a complete data package will need to be submitted by the vaccine manufacturer / supplier to the APVMA detailing information on safety, efficacy, duration of protection and small scale application in the field.
As the vaccine contains soluble forms of the Hendra virus G glycoprotein (sG), vaccinated horses will test positive on the current Hendra virus ELISA test. A DIVA test (Differentiating Infected and Vaccinated Animals) has been developed by the Australian Animal Health Laboratory at Geelong but has not yet been validated. Samples will currently be submitted to AAHL for DIVA testing where a vaccinated horse has signs consistent with potential Hendra virus infection.
Vaccinated horse may be ineligible for export as they will test serologically positive to Hendra virus. Countries that require negative serology include Hong Kong, Singapore, Malaysia, Indonesia and the United Arab Emirates. The Department of Agriculture, Fisheries and Forestry is endeavoring to address this issue through negotiations with our trading partners.
As of 20 December 2012, only 913 horses in NSW have been vaccinated with the new vaccine3. Issues that may have impacted negatively on vaccine uptake include:
- high cost associated with vet only administration,
- lack of safety data,
- desire to ensure horse can be exported.
NATIONAL RESPONSE POLICY
A revised national response policy for Hendra virus was drafted by a small working group including members from the Australian Animal Health Laboratory, Biosecurity NSW, Animal Health Australia and the Queensland Department of Agriculture, Fisheries and Forestry. The new policy was circulated to industry and the Communicable Disease Network Australia for comment and is expected to be submitted to Animal Health Committee for endorsement early in 2013. Significant changes include:
- earlier testing of in contact animals to minimise the period of quarantine and monitoring (at 12 and 20 days rather than 16 and 32 days post contact),
- additional guidance on epidemiological assessment of contacts, tracing and management of infected premises,
- information on the new vaccine,
- revised sampling advice, and
- a revised definition of an infected animal (reflecting issues with interpretation of test results that arose in 2012).
Acknowledgements
Thanks to Barbara Moloney for providing the Map at Figure 1.
References
- www.daff.qld.gov.au as 7 Dec 2012
- www.daff.qld.gov.au as 7 Dec 2012
- Pfizer Animal Health, personal communication