Hendra & Nipah viruses

Victorian statutory requirement

Notification is not required however any new case of these emerging infections should be discussed with the Department of Human Services as a matter of urgency.

School exclusion is not required.

Infectious agent

Two distinct, but closely related RNA viruses of the family Paramyxoviridae: Hendra virus which has so far only been detected in Queensland, and Nipah virus which has been confined to the Malay Peninsula.

Identification

Clinical features
Both viral diseases may cause acute infection with a variety of symptoms including fever, headache, shortness of breath, dizziness, drowsiness and confusion. Two of the three recorded cases of Hendra virus in humans were fatal. One death was due to septic pneumonia while the other was due to severe encephalitis.

In clinical cases of Nipah virus infection encephalitis is the major manifestation, often leading to coma and death in three to thirty days. The case fatality rate for clinical cases approaches 50%. The frequency of subclinical infections is unknown.

Method of diagnosis
The diagnosis can be made by the detection of specific neutralising IgM and IgG antibodies to either virus. Testing is available through the CSIRO Australian Animal Health Laboratory at Geelong. The diagnosis can also be confirmed by virus isolation from infected tissues.

Incubation period

The incubation period varies from four to18 days and rarely up to three months (Hendra virus).

Public health significance & occurrence

Hendra and Nipah viruses are recently recognised zoonotic viral diseases. Hendra virus appears to have emerged from fruit bats in Australia. Horses are the intermediary host most commonly associated with human infection. The first described outbreak of Hendra virus infection occurred in the Brisbane suburb of Hendra in 1994, involving 21 horses (14 fatal cases) and two of their human handlers (one fatal case). A smaller outbreak occurred in 1995 involving two horses and a farmer from the northern Queensland town of Mackay.

The presumed reservoir for Hendra virus is the fruit bat, the Australian flying fox (Pteropus spp.), which appears to be an asymptomatic host. A 20% seropositive rate to Hendra virus has been found among Pteropus bats in Queensland. Wildlife workers who frequently come in to contact with Australian bats have very low seropositive rates.

Nipah virus (named after the Baru Sungai Nipa village in Malaysia) is closely related to Hendra virus. Nipah virus may also have emerged from fruit bats. Pigs are the most common intermediary host associated with human infection. The virus was first identified in 1999 during the investigation of an outbreak in several pig-farming provinces on the Malay Peninsula. The outbreak began in 1998 and resulted in 265 confirmed human cases with 105 deaths in Malaysia and Singapore.

No human or animal cases of Hendra or Nipah viral disease have been detected in Victoria.

Reservoir

Fruit bats (Pteropus spp.) are the primary reservoir for both viruses and appear to be asymptomatic carriers. Horses are the most likely intermediary host in human infection for Hendra virus although other species such as cats show serological evidence of exposure.

Pigs are the most likely intermediary host for Nipah virus although seropositive horses and dogs have been identified.

Mode of transmission

The mode of transmission is unknown although a respiratory route is suspected. Human infection has been most commonly associated with direct contact with infected horses (Hendra) or infected pigs (Nipah). Symptomatic infections also occur in cats and other animals. Both viruses have been isolated from the urine of infected bats and other infected animals.

Period of communicability

There is no evidence of person to person transmission.

Susceptibility & resistance

Unknown.

Control measures

Preventive measures
In an outbreak setting the public should be advised to avoid contact with possible animal sources, particularly bats.

Control of case
Treatment is primarily supportive as there is no proven specific treatment. An uncontrolled trial of the antiviral drug ribavirin has suggested it may reduce the mortality in Nipah virus encephalitis. Expert treatment advice should be sought from an infectious diseases physician.

Control of contacts
No person to person transmission has been observed.

Control of environment
See Outbreak measures, below.

Outbreak measures

A single confirmed case of either of these emerging viral infections would constitute an outbreak.

Case investigation determines the likely source of infection through a detailed history of the patient’s work and travel history.

Further cases may be identified through active case finding amongst close contacts with similar exposure, as well as animal source detection if the infection was acquired in Australia.

In the event of a case being linked to exposure in Victoria or elsewhere in Australia, the Department would work closely with relevant animal health authorities and scientists to control possible sources of infection.

Measures could include:

appropriate protective equipment and hygiene practices for animal handlers and investigators on implicated farms or properties
slaughter of infected horses, pigs, or other animals with burial or incineration of carcasses

restriction of movement of horses or pigs from infected farms or designated areas.

International measures

Prohibition of export of animal products from affected areas.

Additional sources of information

McCormack, JG, Allworth, MA 2002, ‘Emerging viral infections in Australia,’ Med J Aust, vol. 177, pp. 45–49.
Patterson, DL, Murray, PK, McCormack, JG 2000, ‘Zoonotic disease in Australia caused by a novel member of the Paramyxoviridae’, Clin Infect Dis, vol. 27, pp. 112–8.

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