Hendra virus (formerly called equine morbillivirus) is a member of the family Paramyxoviridae. The virus was first isolated in 1994 from specimens obtained during an outbreak of respiratory and neurologic disease in horses and humans in Hendra, a suburb of Brisbane, Australia.
Only three human cases of Hendra virus disease have been recognized. Two of the three individuals known to be infected had a respiratory illness with severe flu-like signs and symptoms. Infection with Nipah virus was associated with an encephalitis (inflammation of the brain) characterized by fever and drowsiness and more serious central nervous system disease, such as coma, seizures, and inability to maintain breathing.
Illness with Nipah virus begins with 3-14 days of fever and headache. This is followed by drowsiness and disorientation characterized by mental confusion. These signs and symptoms can progress to coma within 24-48 hours. Some patients have had a respiratory illness during the early part of their infections.
The natural reservoir for Hendra virus is thought to be flying foxes (bats of the genus Pteropus) found in Australia. The natural reservoir for Nipah virus is still under investigation, but preliminary data suggest that bats of the genus Pteropus are also the reservoirs for Nipah virus in Malaysia.
Hendra virus caused disease in horses in Australia, and the human infections there were due to direct exposure to tissues and secretions from infected horses. Nipah virus caused a relatively mild disease in pigs in Malaysia and Singapore. Nipah virus was transmitted to humans, cats, and dogs through close contact with infected pigs.
In Australia, humans became ill after exposure to body fluids and excretions of horses infected with Hendra virus. In Malaysia and Singapore, humans were infected with Nipah virus through close contact with infected pigs.
These diseases can be prevented by avoiding animals that are known to be infected and using appropriate personal protective equipment devices when it is necessary to come into contact with potentially infected animals.
Laboratory tests that are used to diagnose Hendra virus (HV) and Nipah virus (NV) include detection of antibody by ELISA (IgG and IgM), real time polymerase chain reaction (RT-PCR), and virus isolation attempts. Laboratory diagnosis of a patient with a clinical history of HV or NV can be made during the acute and convalescent phase of the disease by using a combination of tests including detection of antibody in the serum or the cerebrospinal fluid (CSF), viral RNA detection (RT-PCR) in the serum, CSF, or throat swabs, and virus isolation from the CSF or throat swabs.
One of the three Hendra virus infections was marked by a delayed onset of progressive encephalitis. Serious nervous disease with Nipah virus encephalitis has been marked by some sequelae, such as persistent convulsions and personality changes.
Two of the three human patients infected with Hendra virus died. During the Nipah virus disease outbreak in 1998-99, 257 patients were infected with the virus. About 40% of those patients who entered hospitals with serious nervous disease died from the illness.
The drug ribavirin has been shown to be effective against the viruses in vitro. Drug investigations to date have been inconclusive and the clinical usefulness of these drugs is uncertain.
The distribution of these agents in their natural reservoirs will eventually define the geographic range of the threat the viruses pose. However, these viruses are recent discoveries, and much work remains to be done on their geographic distribution and the reservoir species. The occurrence of the disease in humans has been associated only with infection of an intermediate species such as horses with Hendra and swine with Nipah virus. Early recognition of the disease in the intermediate animal host is probably the most crucial means of limiting future human cases.
K Murray, P Selleck, P Hooper, et al. A morbillivirus that caused fatal disease in horses and humans. Science 1995, 268:94-7.
JD O'Sullivan, AM Allworth, DL Paterson, et al. Fatal encephalitis due to novel paramyxovirus transmitted from horses. Lancet 1997, 349:93-5.
Chua KB, Goh KJ, Wong KT, et al. Fatal encephalitis due to Nipah virus among pig-farmers in Malaysia. Lancet 1999; 3541257-9.
Paton NI, Leo YS, Zaki SR, et al. Outbreak of Nipah-virus infection among abattoir workers in Singapore. Lancet 1999; 3541253-6.
Lee KE, Umapathi T, Tan CB, et al. The neurological manifestations of Nipah virus encephalitis, a novel paramyxovirus. Ann Neurol 1999; 46428-32.
CDC, Outbreak of Hendra-like virus—Malaysia and Singapore, 1998-1999. MMWR. Apr 9, 1999; vol 48, no 3, 265-269.
CDC, Update: Outbreak of Nipah virus-- Malaysia and Singapore, 1999. MMWR, Apr 30, 1999; vol 48, no 16, 335-337.