This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
In recent months Australia has seen the lengths science will go to to control the potential outbreak of significant infectious diseases. At this stage, Hendra virus is not particularly infectious in humans but is very deadly and some important recent developments have led to increased concern in the scientific community.
Hendra virus is named after the suburb Hendra in Queensland, Australia, where the virus was first detected. It is a member of the henipavirus family which is a sub group of the paramyxoviridae family of viruses. This family has many members that are known to cause diseases in humans (such as measles and mumps) but also dogs, cattle, birds and marine mammals can be infected.
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Henipavirus structure. Credit: Wikimedia
Hendra virus, and the related Nipah virus, have now both been observed in livestock throughout North Eastern Australia and South East Asia which is a big problem as when this zoonotic virus makes the jump into humans it can be deadly. In Australia the biggest concern is for horses. All tallied up 75% of infected horses die or are put down due to Hendra infection and there have been 7 recorded cases of the disease jumping to humans, 4 people succumbed to the infection.
Whilst having the capacity to kill humans and horses yet another organism, the fruit bat, is thought to be the reservoir of infection. The viral infection is largely asymptomatic in the bats but results in the shedding of enormous amounts of virus in the bat urine and faeces which can be inhaled or ingested by horses resulting in infections. Horses can infect each other, probably through saliva, and the path to humans probably involves inhalation of aerosolised saliva from the horse. Transmission directly from bat to human has not yet been documented and it is unknown if this in fact even possible.
The disease presents relatively similarly in horses and humans and the disease has been characterised by haemorrhages and oedemas throughout the respiratory system but fatally has also resulted in meningitis in the documented human cases.
The identification of fruit bats as the reservoir for infection presents a huge problem for infection control as the bats are a protected species and cannot be culled. They are also a difficult species to remove from an area and so livestock producers continually fear infection from the fruit bat populations.
Earlier this year the alarm bell sounded louder than ever after news that a dog from a property containing infected horses had also tested positive for Hendra marking the only recorded instance of either bat or horse to dog (as the exact path is unsure) transmission and the dog had to be put down. While the transmission to dog does not make the virus more dangerous necessarily it represents a worrying situation where there is enough virus being shed in these regions that non-traditional hosts are able to be infected.
But there may be a solution. As they so often do, a vaccine for Hendra virus may be able to limit the spread to horses and other potential livestock hosts and so limits the chance of subsequent human exposure. Australia’s governmental science organisation, the Commonwealth Scientific and Industrial Research organisation (CSIRO), have 10 full-time staff (called the bat-pack) dedicated to various aspects of Hendra research. In addition to the vaccine, further efforts are being made to understand bat ecology as a predictive tool for potential outbreaks and how the bat faeces and urine is able to carry the virus from bat to horse.
So while it has been all bad news in the past there might be an opportunity to deal with this particular emerging human pathogen early and nip this one in the bud.
References
http://www.abc.net.au/news/specials/hendra-virus/ - last accessed 25th Sept. 2011
Williamson MM, & Torres-Velez FJ (2010). Henipavirus: a review of laboratory animal pathology. Veterinary pathology, 47 (5), 871-80 PMID: 20682803
Aguilar HC, & Lee B (2011). Emerging paramyxoviruses: molecular mechanisms and antiviral strategies. Expert reviews in molecular medicine, 13 PMID: 21345285
Vigant F, & Lee B (2011). Hendra and nipah infection: pathology, models and potential therapies. Infectious disorders drug targets, 11 (3), 315-36 PMID: 21488828