Further victims as Hendra outbreak continues

While Queensland and NSW authorities continue the struggle to control the latest hendra outbreak, the virus claimed an unexpected victim almost six weeks after the first case was detected.

Towards the end of July a pet dog from a property where three infected horses had already been found tested positive to Hendra antibodies, and was subsequently put down.

At the time of writing Hendra had claimed the lives of at least 15 horses in Queensland and NSW, while over 60 people were still being monitored for signs of infection, including several vets.

All four species of fruit bats found in Australia are carriers of the Hendra virus.

Queensland’s chief vet Rick Symons said it was unclear how the two-year-old kelpie had contracted Hendra, but it did not necessarily indicate the virus was evolving.

“We know the virus is stable, and we’re not seeing different strands of it. We know the property had three horses affected – we know transmission has occurred on that property. We know that one of the horses lay for a while, and that the dog had access to the horse. Dogs are inquisitive – it could have licked horse discharge,” Symons said.

Of the two other dogs on the property one tested negative, while the other remains under observation. All cats and dogs on 11 other quarantined Queensland properties have returned negative tests for the virus.

Tests were run on several species of domestic animals following the first outbreak in 1994, which was responsible for the deaths of 20 horses and one person. Of the animals injected with Hendra, cats and guinea pigs were found to be the most susceptible. While these animals all fell sick and shed virus, dogs, mice and ferrets showed little clinical reaction, and did not shed virus.

Responding to the first known case of a dog contracting the virus outside of laboratory conditions, federal, Queensland and NSW state governments have provided up to $12 million additional funding towards research to combat the disease. It is expected the extra resources will enable scientists to examine virus biology, as well as gain a clearer understanding of its impact on human and animal health, and environmental biodiversity.

Their principal focus will be to examine:

  • What causes the virus to spill over from flying foxes?
  • How are horses and other animals exposed to Hendra virus?
  • Why has 2011 seen a spike in cases?

“The increase in Hendra incidents this year, and the announcement of a positive case in a dog, has raised new questions and challenges for our scientists. Queensland and NSW have committed funding of $3 million each to build on and accelerate research already underway into how the virus transmits from flying foxes,” Queensland premier Anna Bligh said.

According to Hume Field, Principal Veterinary Epidemiologist (Emerging Diseases) at Biosecurity Queensland, bats are increasingly recognised as a reservoir for a range of emerging diseases, that includes Hendra and Australian bat lyssavirus, and he believes the perception these diseases are on the rise is due to ecological changes that have provided opportunities for increased contact with bats.

“Habitat fragmentation, population dynamics, and encroachment into natural areas – these kinds of factors create an epidemiological bridge from bats to livestock or people,” Hume said.

Although there have been calls from members of the public and community leaders to cull fruit bat colonies, or have them dispersed in the interest of public safety, Symons said no direct scientific evidence linking the dispersal of bat colonies to the spread of Hendra had been found, and that moving the animals may be counter-productive, given the body of evidence that suggests more virus is secreted when bats are stressed.

“There is scientific evidence that nutritional stress and reproductive stress leads to higher levels of virus in flying foxes. We haven’t any definitive research on whether the dispersal in itself causes the spread of Hendra, but we should be aware there is a possibility dispersing them will cause stress and cause an increase in virus load,” he said.

Field agreed culling should not be considered, since other bat colonies would simply move in and occupy vacated spaces.

While they agreed the effectiveness of culling programs would be lessened because of bats’ high mobility, animal advocates have expressed concern that animals not killed cleanly would suffer needlessly. And as well as increased stress levels, the contamination of wide areas from injured and dead bats would increase the risk of spreading the Hendra virus more widely.

Scientists from Geelong’s Australian Animal Health Laboratory are working towards a position whereby a vaccine can be made available ‘as soon as sufficient data has been generated to ensure that it meets the required safety and efficacy targets’.

Veterinary pathologist and research team leader Deborah Middleton said Biosecurity Australia, the Australian Quarantine and Inspection Service, and the Australian Pesticides and Veterinary Medicines Authority had all indicated they would ensure their own assessment processes were streamlined to facilitate the earliest possible release.

“Some of the additional data will be provided by field trials and we are working to have these commence in early 2012. How the animals will be selected for that work and how many vaccine doses will be made available is yet to be determined. One point of comparison is that the accelerated approvals for the Equine Influenza vaccine were done on a background of safety in the target animal species that had been tested in hundreds of thousands of horses over several years,” Middleton said.

Given the combined Queensland and NSW research effort it is anticipated a vaccine will be publicly available in 2013, following next year’s expanded clinical trial program that is expected to have the potential to deal with related viruses in other parts of the world.

While the AAHL’s post-exposure treatment work will also be continued, Middleton said plans to actively pursue side-stall testing research have been shelved.

“We are continuing to work on optimising the regime for post-exposure administration of the monoclonal antibody that targets the Hendra G glycoprotein. Our current data indicates that the optimum effect of a single dose is achieved when the treatment is administered very soon after exposure, so we are exploring whether higher loading doses or multiple doses can have an impact once fever or other clinical signs have become established,” she explained.

Field believes Hendra is present every year, but described this year’s cluster outbreak as an ‘aberration’.

“High rainfall disrupted the flowering season, which has impacted on the bats’ immune systems, and left them undernourished and stressed,” he said.

While she admitted science ‘does not yet fully understand the disease’ premier Bligh urged people to keep their family members and pets away from sick horses, and said state governments were ‘determined to beat Hendra virus, and will apply every scientific effort.’

For the latest information contact Biosecurity Queensland on 13 25 23, or visit www.biosecurity.qld.gov.au.

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