The Nipah virus is a new virus "discovered" in 1999 responsible for a zoonosis that causes the disease in animals and human beings after contact with an infected animal. It takes its name from the place where it was found for the first time in Malaysia. The Nipah virus is closely related to another recently discovered (1994) zoonotic virus, called the Hendra virus, from the name of the town where it developed for the first time in Australia. The Nipah virus and the Hendra virus belong to the family of Paramyxoviridae. While the members of this group of viruses are only responsible for a few limited outbreaks, the biological capacity of these viruses to infect a wide range of hosts with a high mortality rate in human beings has made this emerging viral infection a public health concern.
Some species of frugivorous bats are now thought to be the natural hosts of the Nipah and Hendra viruses. Their geographical distribution covers an area including the north, east and south of Australia, Indonesia, Malaysia, the Philippines and some Pacific islands. The bats appear to be receptive to infection by the viruses but do not themselves become ill. It is not known how the virus is transmitted from bats to animals.
The method by which transmission occurs between animals and from animals to human beings is poorly understood, although it appears to require close contact with the infected tissues or organic fluids of infected animals. Anti-Nipah antibodies have been found in pigs and other domestic and wild animals. The role of species other than pigs in transmitting the infection to other animals has not been established yet.
It is unlikely that the Nipah virus is transmitted easily to human beings, although previous reports suggest that it passes more easily from animals to human beings than the Hendra virus. Despite frequent contact with frugivorous bats, no serological traces of infection are found in people who look after them. Pigs appear to have been the origin of the infection in most human cases in the Malaysian outbreak that occurred in Nipah, although other sources such as infected dogs or cats cannot be excluded. No cases of human to human transmission of the Nipah virus have been reported.
The incubation period is between 4 and 18 days. The infection is often mild or silent (subclinical). In symptomatic cases, the disease usually begins with a "flu-like" syndrome, with high temperature and muscle pain (myalgia). It can progress to inflammation of the brain (encephalitis) accompanied by drowsiness, disorientation, seizures and coma. Fifty percent of declared clinical cases are fatal.
No medical treatment has yet been shown to be effective against Nipah virus infection. Above all, treatment is by intensive support. Early treatment with ribavirin, an anti-viral agent, appears to reduce both the duration and severity of the febrile illness. Hozever, it is not yet known, whether or not this treatment can cure or improve survival.