Horse vaccination the most effective direct solution to reducing Hendra risk, say scientists

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The Hendra virus is transmitted from animals to humans and is a Bio-Safety Level-4 disease agent, which is the most dangerous level in the world.
The Hendra virus is transmitted from animals to humans and is a Bio-Safety Level-4 disease agent, which is the most dangerous level in the world. This requires scientists to wear fully encapsulated suits with their own air supply. © CSIRO

Cases of Hendra virus in Australia are likely to spread further south and inland because of climate change, according to the authors of a just published review.

The Hendra virus, first identified in 1994, is carried by flying fox fruit bats. It is capable of infecting horses and humans.

Since 1994, there have been 63 spillover events identified involving 105 horses and seven humans. Four people have died from Hendra.

The review team, with the School of Veterinary Science at the University of Queenland and the Australian Centre for Disease Preparedness, part of the science agency CSIRO, said vaccination of horses remains the most effective direct solution to prevent disease transmission to horses and protect humans.

“Vaccination breaks the chain of infection,” they said.

No horse that has received the vaccine has tested positive for Hendra virus infection, they said.

“All unvaccinated ill horses in areas where flying foxes exist, may potentially be infected with Hendra virus, posing a significant risk to the veterinary community,” Ka Yuen and his colleagues wrote in the journal One Health.

Outbreaks in horses have tended to cluster in winter, they noted, overlapping with the foaling season, when veterinarians and horse owners can be in close contact with horses and their bodily fluids, increasing the risk of transmission.

The scientists said there were some important knowledge gaps around Hendra.

Immunity in foals to the virus from transfer of passive immunity and vaccination remains unknown, and current vaccination recommendations may need revision.

There was scope, they said, to reduce turnaround time through better correlation of diagnostic tests. Development of field-based diagnostics would improve the biosecurity response.

The authors described the likely spread of the virus further south, and inland.

Flying fox distributions are highly dependent on food sources — nectar, pollen and fruit. A lack of food because of tree clearance and climate change may disperse them beyond typical territories.

The bats may also be put under greater stress, which has been linked with virus excretion.

The scientists noted that specific weather patterns have already been linked with virus spillover events.

The territory of Pteropus alecto, the main reservoir bat species, is expanding south, and it was predicted Hendra cases would occur in the Hunter Valley, an important Australian hub for Thoroughbred racehorses.

A year after the prediction, the first and southernmost case of the virus was recorded in June 2019 in the Upper Hunter Valley.

The scientists said strict specific biosecurity protocols should be implemented to protect veterinary staff from the virus. They described a biosecurity protocol suitable for veterinary hospitals, capable of being adapted for a range of situations, in areas with flying foxes.

The review team said that while their review focused on the characteristics of Hendra virus epidemiology around diagnostics and biosecurity, human behaviors and attitudes towards Hendra virus vaccination and associated side effects and adverse events are likely to play a major role in prevention.

The review team comprised Ka Yuen, Natalie Fraser, Joerg Henning, Justine Gibson, Lily Betzien and Allison Stewart, all with the School of Veterinary Science at the University of Queensland; and Kim Halpin, with the Australian Centre for Disease Preparedness, part of the Commonwealth Science and Industry Research Organization.

Ka Y. Yuen, Natalie S. Fraser, Joerg Henning, Kim Halpin, Justine S. Gibson, Lily Betzien, Allison J. Stewart
Hendra virus: Epidemiology dynamics in relation to climate change, diagnostic tests and control measures,
One Health, Volume 12, 2021, 100207, ISSN 2352-7714, https://doi.org/10.1016/j.onehlt.2020.100207.

The study, published under a Creative Commons License, can be read here

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