Hendra virus is a recently discovered virus affecting both horses and humans which, to date, has only been identified in Australia. Although originally named "equine morbillivirus" because of antigenic relationships to other morbilliviruses, more recent data indicates that it is a distinct member of the paramyxovirus family.

History:

Hendra virus first appeared in August, 1994, at a stable in Mackay, Australia, with a second outbreak in September, 1994 near Brisbane, Australia. In the later outbreak, infection killed 14/21 horses and their trainer. A second stable hand became ill, but recovered. A third human case was subsequently defined- the husband of a veterinarian who helped with the postmortem on one of the first horses killed in Mackay. This individual developed a mild, meningoencephalitis shortly after the postmortem, but recovered, only to die in October, 1995 of recurrent encephalitis.

In February, 1999, another case of Hendra virus infection was identified in a horse in Australia. This horse died after only 24 hours of clinical illness. To date, there have been no human cases associated with this horse, nor other infected horses.

Clinical signs in the horses:

• fever, lethargy
• respiratory distress
• ataxia, head pressing

Symptoms in humans:

• The same mixture of respiratory and neurologic signs seen in horses extended to the humans involved, although either respiratory or neurologic signs tended to predominate in each individual.

Where did this virus come from?

No other evidence of Hendra virus infection was uncovered by extensive serologic screening of horses in Australia, and serologic screening for infection in 46 species of other domestic and wild animals near the original farms of origin did not initially reveal any reservoir of infection. However, in May 1996, antibodies against Hendra virus were detected in "flying fox" fruit bats, and more recently Hendra virus has been isolated from uterine fluid and fetal tissues of flying fox bats. Although the precise epidemiologic relationship between these bats and infected horses/humans remains to be elucidated, it is now thought that Hendra virus is a bat virus that has evolved the ability or opportunity to infect other species. Of great interest is the fact that since the original discovery of Hendra virus, two other novel paramyxoviruses have been isolated in Australia (Menangle virus) and Malaysia (Nipah virus), both of which also may be derived from fruit bats.

References:
Anonymous. 1996. Another human case of equine morbillivirus disease in Australia. Emerg. Infect. Dis. 2:71-72.

Halpin, K. et al. 2000. Isolation of Hendra virus from pteropid bats: a natural reservoir of Hendra virus. J. Gen. Virol. 81:1927-1932.

Murray, K. et al. 1995. A morbillivirus that caused fatal disease in horses and humans. Science 268:94-97.

Murray, K. et al. 1995. A novel morbillivirus pneumonia of horses and its transmission to humans. Emerg. Infect. Dis. 1:31-33.

O'Sullivan, J.D. et al. 1997. Fatal encephalitis due to novel paramyxovirus transmitted from horses. Lancet 349:93-95.

Wang, L.-F. et al. 1998. A novel P/V/C gene in a new member of the Paramyxoviridae family, which causes lethal infection in humans, horses, and other animals. J. Virol. 72:1482-1490.

Williamson, M.M. et al.. 1998. Transmission studies of Hendra virus (equine morbillivirus) in fruit bats, horses and cats. Aust.Vet. J. 76:813-818.

Young, P.L. et al. 1996. Serologic evidence for the presence in Pteropus bats of a paramyxovirus related to equine morbillivirus. Emerg. Infect. Dis. 2:239-240.

Yu, M. et al. 1998. Sequence analysis of the Hendra virus nucleoprotein gene - comparison with other members of the subfamily Paramyxovirinae. J. Gen. Virol. 79:1775-1780.

Yu, M. et al. 1998. The attachment protein of Hendra virus has high structural similarity but limited primary sequence homology compared with viruses in the genus paramyxovirus. Virology 251:227-233.