Nipah virus

Belongs to the genus Henipavirus in the family Paramyxoviridae

Nipah virus has not been found in Australia.

Nipah virus was first described after a major outbreak of disease in pigs and humans in Malaysia in early 1998 and Singapore in 1999. The outbreak resulted in the death of 105 people out of 256 affected and the culling of over 1 million pigs.

Since then, there have been regular reports of clusters of cases in humans in Bangladesh and India. In contrast to the Malaysian outbreak, some of these clusters appear to involve direct bat-human transmission, and some have evident human-to-human transmission.

Evidence of infection with Nipah or a related virus has been found in bats from Indonesia to Africa.

Fruit bats

Incubation period is 4–14 days. Pigs are highly infectious during this period.

Pigs

This is a highly contagious disease in pigs. The majority of infections in pigs are asymptomatic, but symptomatic cases show acute fever, laboured breathing, and neurological signs such as trembling, twitching and muscle spasms. Generally, mortality is low (less than 5%), except in young piglets.

The clinical course of the disease appears to vary with age. Sows primarily present with neurological disease, but sometimes die suddenly without evident signs. In weaners and porkers, a respiratory syndrome predominates, frequently accompanied by a harsh non-productive (loud barking) cough. Apparent high mortality rates in piglets may indirectly reflect infection in sows and inability to effectively suckle piglets.

Other animals

Infection in horses, dogs and cats was also a feature of the Malaysian outbreak. Clinical signs ranged from asymptomatic to severe febrile illness, with respiratory or neurologic presentation.

Humans

As Nipah virus outbreaks in pigs have been associated with human cases, early detection of the disease is important in reducing the risk to people.

Nipah virus infection in people can be asymptomatic, or can result in a spectrum of clinical manifestations, from fever, muscle pain and vomiting, through to pneumonia and encephalitis. Chronic neurological symptoms and relapsing or recurring encephalitis has been recorded.

The case fatality rate in people is estimated at 33–100% (average 52%).

Fruit bats are the natural host for the virus. The first reported outbreak of Nipah virus infection in Malaysia in 1998 is thought to be due to a combination of factors: land-use change resulting in habitat loss, encroachment of pig farms into remnant habitat, and the local farming practice of planting fruit trees close to pig sheds. Infection spread locally, and subsequently more widely, as a result of the movement of asymptomatic pigs for trade. The majority of human cases had a history of direct contact with sick pigs or their contaminated tissues.

In the Bangladesh and India outbreaks, the primary source of infection for people appears to be consumption of date palm sap contaminated with urine or saliva from infected fruit bats.

Direct human-to-human transmission has also been recorded in outbreaks in Bangladesh in 2004, but it is unclear whether transmissibility reflects cultural practices or variation in strain pathogenicity.

During outbreaks of disease in pigs in Malaysia, the spread of infection was readily controlled by a variety of measures, including quarantining infected premises, controlling animal movements, culling pigs, burying or incinerating infected carcasses, and decontaminating.

There are currently no effective treatments for Nipah virus infection.