Hendra virus (Hendra henipavirus)
Hendra virus (Hendra henipavirus) is a rare and serious zoonotic illness primarily affecting horses and occasionally humans, originating from Australia. First identified in 1994 in Hendra, a suburb of Brisbane, the virus is transmitted from flying foxes, large Australian bats, to horses, typically through the bats’ urine. The disease can lead to severe respiratory symptoms in both horses and humans, with a high mortality rate; approximately 80% of infected horses and 57% of known human cases have resulted in death. In humans, symptoms may include a dry cough, fever, confusion, and in severe cases, can lead to encephalitis or septic pneumonia. Over the years, there have been limited outbreaks, primarily in northeastern Australia, with a total of seven known human infections, resulting in four fatalities. Although direct transmission from bats to humans has not been observed, caution is advised for those working with horses, particularly those showing symptoms. Preventive measures emphasize hygiene and the use of protective gear to mitigate risks. Research into potential treatments, including the antiviral ribavirin and antibody therapies, is ongoing, but conclusive results are still needed.
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Hendra virus (Hendra henipavirus)
Hendra virus (Hendra henipavirus) is a rare illness occurring among horses and some humans on the northeastern coast of Australia. The disease was first identified after an outbreak in the Brisbane, Queensland, Australia, suburb of Hendra. There, in 1994, twenty-one horses and two workers contracted the illness. Primarily a respiratory disease, Hendra is zoonotic, meaning it is transferred between animals and humans. Hendra most likely originated in flying foxes (large Australian bats) whose urine infected horses. Some of the horses then infected humans. Four humans and more than one hundred horses have died of Hendra since 1994.
Background
Hendra virus was discovered in 1994 in Hendra, a suburb of Brisbane, Queensland, Australia. There, the virus appeared in two people and twenty-one horses at a racing stable. The initial human cases were a forty-nine-year-old horse trainer and a forty-year-old stable worker. The trainer experienced a fatal fulminating pneumonic illness, while the stable worker lived through a flu-like sickness. Both of the people had been in close contact with ill horses and had become infected through the horses’ respiratory moisture and body fluids. Approximately ninety other people who had worked at or visited the stable were monitored, but they did not show symptoms.
The Hendra virus has since claimed the lives of more than one hundred horses in Queensland and New South Wales. Between 1994 and 2024, seven humans were infected, with four dying of the virus. According to the World Health Organization, all the viral incidents took place along the northeastern coast of Australia. These incidents included Brisbane in 1994 and 2008; Mackay in 1994; Cairns in 1999 and 2004; Townsville in 2004; Murwillumbah in 2006; Peachester in 2006 and 2007; Clifton Beach in 2007; Proserpine in 2008. An additional equine case took place in Queensland in 2022 and in 2023, a horse died of the Hendra virus in the Newcastle Hunter region of New South Wales.
Overview
Hendra virus is a form of zoonotic illness, or a disease that may be transmitted from animals to humans, or, in some cases, from humans to animals. One of the most well-known zoonotic diseases is rabies, a nervous-system disorder resulting from a virus transmitted by the bite of an infected creature. Some other zoonotic diseases include trichinosis, salmonella, psittacosis, anthrax, and plague.
Scientists have determined that the Hendra virus most frequently originates among flying foxes, large bats native to Australia, South and Southeast Asia, and East Africa. Flying foxes are a natural reservoir for the virus but do not demonstrate any remarkable symptoms or behaviors when they are carrying it. The virus is most likely transferred through flying fox urine to horses, which may then infect other horses, dogs, or humans. Although it may be scientifically possible, transmission from flying foxes directly to humans, from humans to horses, or from humans to other humans has not been observed.
The Hendra virus is a rare disease and, even in areas with significant populations of flying foxes, horses are statistically very unlikely to become infected. However, among those horses who do become infected, the mortality rate is about 80 percent. Among infected horses, symptoms may include elevated temperature and heart rate, sweating, and frothing mucus around the nose. In more serious cases, the symptoms may also include muscle weakness or spasms, difficulty balancing, and rapid physical deterioration leading to death.
For infected humans, the viral incubation period usually lasts from around 9 to 16 days. When the virus fully emerges, it can lead to serious respiratory illness with many of the signs and symptoms of influenza. More specifically, the symptoms of human infection may involve a dry cough, a sore throat, difficulty in breathing, or fever. Symptoms may also include headache, dizziness, fatigue, and confusion. For some patients, the illness may lead to encephalitis, an inflammation of the brain most commonly linked to viral infections, or a severe and destructive lung infection known as septic pneumonia. The human fatality rate for the Hendra virus, based on the seven known cases, is high, at 57 percent.
People who may have been infected should undergo testing. Preliminary tests include examining a person’s medical history and lifestyle factors, determining whether a person has been in close contact with a potentially infected horse, and performing a physical exam and blood tests. Biopsies of infected tissue may also provide valuable insights. Laboratory tests may include detection of antibodies or attempts to isolate the virus. (Antibodies are blood proteins produced by the body to counteract foreign or harmful substances within the body.) Another potential option is real-time polymerase chain reactions, which involves close study of a DNA sample. Any person suspected of having Hendra virus should be treated in highly controlled and contained environments to prevent spread of the disease.
The Hendra virus may be treatable. Medical experts have identified a drug called ribavirin as potentially helpful in combating the virus within the human body, although testing has been limited and inconclusive. A form of therapy employing a neutralizing antibody for Hendra (along with the related Nipah virus) has proven effective among infected animals. Australian scientists are experimenting with adapting this approach for use in human patients.
Caution and hygiene are two important means of reducing further Hendra virus outbreaks. Horses that demonstrate symptoms of the virus or die suddenly of neurological or respiratory illness should be considered potential carriers. Suspected carriers should be isolated at least fifteen feet (five meters) from other horses, humans, and dogs, or kept behind a protective wall, and treated with caution. Humans who work with horses, particularly ill horses, should practice all possible hygiene and safety measures to reduce their chances of becoming infected. Personal protective gear and frequent washing of hands and clothing are essential to avoiding possible infection.
Bibliography
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