We, as horse owners and veterinarians, often become quite complacent regarding certain diseases found elsewhere in the world–Diseases that if here, would wreak havoc in our human and horse populations. We know such disease entities exist, but often we know very little about them and rely strictly on the Department of Agriculture and its officials to keep them out of our country by enforcing various laws and regulations dealing with the importation of livestock and merchandise.
Occasionally, a disease will make it through the defense system and will have to be reckoned with. A prime example would be West Nile. The West Nile virus was known for many years in Africa, Europe and Asia, but only recently made it to North America. Quite possibly, it was brought here by an infected mosquito who hitched a ride on an airplane.
I will have to admit my knowledge of the disease, Hendra, was almost nil until I received, by E-mail, a 13-page report on the condition entitled “Research Update: Hendra Virus.” It was prepared by Dr. Jo Edmondston and Dr. Hume Field for “2009–Australian Biosecurity CRC for Emerging Infectious Diseases.” The report on the emerging virus disease is very well-written and it is from this source of information that my knowledge of Hendra has been gained.
In 1994, the Hendra virus was first isolated from an outbreak of a disease which occurred in a racing stable located in the Brisbane, Australia, suburb of Hendra. In this outbreak, 13 horses died and another seven head, which had been exposed, were destroyed to minimize the risk for further spread of the disease. In this outbreak a horse trainer and a stable hand became extremely ill. The horse trainer died. Both of these individuals had very close contact with the sick horses.
What are the symptoms of this disease known as Hendra? They are: acute onset, in horses, with a rise in temperature and heart rate, accompanied by respiratory or neurological symptoms leading to a rapid onset of death.
The incubation period of Hendra virus in the horse is five to 16 days and in humans is five to 14 days. Seventy-five percent of horses die from acute infection two days after the first symptoms of the disease appear.
According to the information provided on the Hendra virus incidents, there have been 12 outbreaks in Australia since 1994, in which 44 horses either died or were euthanized. In these incidents there were seven people, who after close contact with some of the infected horses, became ill with influenza-like symptoms. Three of these people recovered but four died.
In 1994, after the Hendra virus was isolated and identified, it became imperative to find its source in nature. From the start of the investigation a total of 169 animals were checked for antibodies for the Hendra virus and found to be negative.
According to the report I have read, by early 1996, a break came in the investigation. The Hendra virus antibodies were discovered in several species of the fruit bats known in Australia as Australian flying foxes.
There are four species of flying foxes in Australia native to the country. They are the little red flying fox, grey headed flying fox, black flying fox and the spectacled flying fox. The mammals feed on fruit and plant seeds and it is known that they play a very important role in pollination and seed dispersal for at least 290 plant species.
Scientists studying over 5,000 serum samples from 46 species of animals, in Australia, found no evidence of antibodies from the Hendra virus except in flying foxes as well as horses and humans which had been involved in the previous incidents. Ongoing scientific studies of the Australian flying foxes seem to point to them as the natural reservoir of the Hendra virus.
How does the Hendra virus get from the flying fox to the horse? The exact method is not known but scientists think a horse eats grass or partially eaten fruit which is contaminated with bat urine, saliva or other bodily fluids such as birthing fluids. Of course these fluids have to contain the Hendra virus as the host bat must be undergoing an active infection, thus shedding lethal Hendra virus in their body fluids.
In all of the studies of the Hendra virus there is no evidence that the virus goes from bat-to-human or human-to-human or human-to-horse, but it does go from bat-to-horse-to human. “The greatest risk of human infection appears to be through the direct physical contact with the body fluids of ill, dying or dead horses.”
There is much research to be done on the Hendra virus, especially its behavior in the wild with the flying foxes. A treatment for the disease is badly needed as well as a vaccine to prevent it.
I thought you'd find this article on an emerging virus disease, with all of its complexities and problems which scientists are trying to understand and manage, of great interest. The world is ever changing, even in the world of the horse.
Information for this article about the disease, Hendra, and the Hendra virus was taken solely from the article I reference earlier.
Many thanks for the paper which was sent to me by my good Australian friend, Ineke Kuiper, publicity officer for the Shire Horse Society of Australia. www.shirehorsesociety.com.au