Key messages

  • Nipah virus infection is a newly emerging zoonosis.
  • Nipah virus infection does not have to be notified, but any new cases should be reported to the department.
  • Human cases range from asymptomatic to those involving fatal encephalitis.
  • The initial outbreaks was in Malaysia in 1998, followed by Singapore, Bangladesh and India.
  • Fruit bats are the natural host, but pigs, horses, goats, sheep, cats and dogs can become ill if infected and transmit the virus.

Notification requirements for Nipah virus infection

Notification is not required; however, any new cases of this emerging virus should be reported to the department as a matter of urgency.

Infectious agent of Nipah virus infection

Nipah virus (NiV) infection is a newly emerging zoonosis. NiV, a member of the Paramyxoviridae family, is a zoonotic virus, which means it can transfer from animals to people.

NiV was first identified during an outbreak in Kampung Sungai Nipah, Malaysia, in 1998. All subsequent outbreaks have occurred in South Asia (India, Bangladesh, Malaysia and Singapore).

Identification of Nipah virus infection

Clinical features

In humans, NiV causes encephalitis (inflammation of the brain) or respiratory signs and symptoms. The case-fatality rate of encephalitis is estimated at 40–75 per cent.

Human cases range from asymptomatic to cases involving fatal encephalitis. Infected people initially develop a flu-like illness with fever, headaches, myalgia (muscle pain), vomiting and sore throat. This can be followed by dizziness, drowsiness, altered consciousness, and neurological signs of acute encephalitis.

Encephalitis and seizures occur in severe cases, progressing to coma within 24–48 hours.

Some people can develop atypical pneumonia and severe respiratory problems, including acute respiratory distress syndrome.

Most people who survive acute encephalitis make a full recovery, but approximately 20 per cent are left with residual neurological deficits, such as persistent convulsions and personality changes.

A small number of people, usually those with mild or subclinical cases, can relapse or develop delayed-onset encephalitis.

Diagnosis

The diagnosis can be made by the detection of specific neutralising IgM and IgG antibodies to the virus, enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR) assay, immunofluorescence assay and virus isolation by cell culture.

The diagnosis can also be confirmed by virus isolation from infected tissues.

Testing is available through the CSIRO Australian Animal Health Laboratory at Geelong.

Incubation period of Nipah virus

The incubation period varies from 4 to 18 days.

Public health significance and occurrence of Nipah virus infection

There are currently no drugs or vaccines available to treat humans with NiV infection. Supportive care and the treatment of symptoms are the main approaches.

No human or animal cases of NiV infection have been detected in Victoria.

Reservoir of Nipah virus

Fruit bats from the Pteropodidae family, particularly the species belonging to the Pteropus genus, are the natural host for NiV, although illness does not occur in the bats.

NiV outbreaks in pigs and other domestic animals (horses, goats, sheep, cats and dogs) were first reported during the initial Malaysian outbreak.

NiV is capable of causing severe disease in pigs and other domestic animals.

Mode of transmission of Nipah virus

During the initial outbreaks in Malaysia and Singapore, most human infections (predominantly of farmers and abattoir workers) resulted from direct contact with sick pigs or their contaminated tissues. Transmission was thought to occur via respiratory droplets, contact with throat or nasal secretions of pigs or contact with the tissue of a sick animal.

In the Bangladesh and India outbreaks, consumption of fruit or fruit products (raw date palm sap/juice) contaminated by infected fruit bats was the most likely source of infection. During those outbreaks, NiV spread directly from human to human through close contact with people’s excretions, secretions and body fluids. In India, transmission from human to human was also reported in a healthcare setting.

From 2001 to 2008, approximately half of the reported cases of NiV infection in Bangladesh were due to human-to-human transmission.

Period of communicability of Nipah virus infection

Unknown.

Susceptibility and resistance to Nipah virus infection

Undetermined. Relapses of infection can occur.

Control measures for Nipah virus infection

Preventative measures

There is no treatment or vaccine available for humans or animals.

In the absence of a vaccine, raising awareness of risk factors and educating people about measures that can reduce the risk of exposure to the virus will reduce the risk of infection.

To reduce the risk of animal-to-human NiV transmission, gloves, gowns, protective eyewear and boots should be worn when handling sick animals or their tissues and during slaughtering and culling, along with good hand hygiene before leaving farms and abattoirs.

To reduce the risk of human-to-human transmission, unnecessary close physical contact with NiV-infected people should be avoided. If person-to person transmission is a possibility, isolation, along with standard, droplet and contact precautions, should be implemented.

Control of case

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

Control of contacts

Asymptomatic contacts require education on transmission prevention and the signs and symptoms of illness.

Symptomatic contacts should be consider for testing, in consultation with an infectious diseases physician.

Control of environment

To reduce the risk of bat-to-human NiV transmission, efforts should focus on:

  • avoiding contact with fruit bats and infected animals such as pigs
  • ensuring that fruit bats are not able to roost close to animal pens
  • reducing bats’ access to date palm sap
  • boiling freshly collected date palm juice and thoroughly washing and peeling fruits before consumption.

Outbreak measures for Nipah virus infection

A single confirmed case of NiV infection constitutes an outbreak.

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

Further cases may be identified through active case finding among close contacts with similar exposure.

If a case is linked to exposure in Victoria or elsewhere in Australia, the department will work closely with relevant animal health authorities and scientists to identify and control possible sources of infection.

Measures could include:

  • testing possible animal sources (fruit bats) and affected animals for the presence of NiV or serological evidence of infection
  • using appropriate protective equipment and hygiene practices for animal handlers and investigators on implicated farms or properties
  • slaughtering infected animals and burying or incinerating the carcasses
  • restricting the movement of animals from infected farms or designated areas.

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