Nipah Virus Disease


The emergence of Nipah virus disease in Malaysia in 1998 illustrates the connection between disease emergence and man's complex relationship with the environment—in particular, the intersection of human behavior with deforestation, habitat encroachment, and modern agricultural methods. Nipah virus disease is an infectious, zoonotic disease caused by the Nipah virus (NiV), one of the viruses in the recently named genus Henipahvirus, and a member of the Para-myxoviridae family of RNA viruses. To date, outbreaks of Nipah virus disease have been limited in number and have occurred in only three Asian countries, but the severity of the disease and its efficient transmission from animals to humans makes understanding and preventing Nipah virus disease a global health priority.


Since about 1920, deforestation in the Malaysian Peninsula has taken place in order to produce pulpwood and palm oil in vast monoculture plantations that grow only Elaeis guineensis, the oil palm tree. This reduced the population of native fig plants and fruitbearing trees available for Malaysia's pteropid bat populations, who foraged farther afield to secure their favorite food sources. Additionally, farms in Malaysia, both plant and livestock operations, often decorate or supplement their growing space with fruit trees, which attracted the displaced bats.

Transmission electron micrograph (TEM) depicts a number of Nipah virus virions that had been isolated from a patient's cerebrospinal fluid (CSF) specimen.

Transmission electron micrograph (TEM) depicts a number of Nipah virus virions that had been isolated from a patient's cerebrospinal fluid (CSF) specimen.
(Science Source/Science Source)

Sometime in the late 1990s, bats who carried the Nipah virus, fed on fruit trees near a pig farming operation in the village of Sungai Nipah in the Malaysian state of Perak, shedding the virus in their saliva and urine, likely dropping bits of contaminated fruit, and providing an opportunity for pigs to acquire, amplify, and pass the virus on to the humans who cared for them. In their role as intermediate host, the pigs did experience illness from Nipah infection, but not to the serious extent that the virus caused as it spilled over into the human population. In September 1998, an outbreak of a serious encephalitis syndrome occurred among workers at a Sungai Nipah pig farm, and quickly spread to nearby farms and then to Singapore, where the pigs were transported for processing. In all, 257 people contracted Nipah virus disease during the initial outbreak and 106 people died. In 1999, the causative virus was recognized as a novel pathogen and given the name Nipah for the area where it first emerged. Since the initial outbreak of Nipah virus disease, at least eight additional outbreaks have occurred in Bangladesh and the neighboring Indian state of West Bengal. No additional outbreaks of Nipah virus disease have occurred in Malaysia.

Risk Factors

Old World fruit bats of the genus Pteropus were confirmed in 2011 as the natural reservoir for Nipah virus, and these bats are found in forested areas of eastern Africa and Madagascar, throughout Asia, Australia, and the Pacific islands. Habitat destruction for monoculture and for building settlements and farms are bringing these bats into increasingly close contact with humans. In Bangladesh and other areas, crowding and lack of improved sanitation facilities facilitate the transmission of Nipah from person to person. Although Nipah virus disease could erupt anywhere pteropid bats carry the virus, risk factors for the disease remain greatest for those who work with pigs or eat raw date palm sap within pteropid bat habitats, and for people in close contact with persons infected with the disease.

Causes and symptoms

Because affected pig farmers in the initial 1998 Nipah virus disease outbreak developed inflammation of the brain, the cause of the outbreak was initially assumed to be Japanese encephalitis, a mosquitoborne disease of the tropics that is endemic (present and occurs periodically) in Malaysia. When mosquito control measures did not slow the outbreak, and officials recognized that most infections continued to occur in adult males (Japanese encephalitis is more common in children), scientists began to seek the cause elsewhere, eventually focusing on bats as the primary reservoir of the virus that causes the disease. The bats infected pigs on the farms, and the pigs served as an intermediate host. The pigs amplified the virus into an efficient pathogen for infecting the men who worked in the pig farms in Malaysia, along with those who worked in plants that processed the pork in Singapore.

Later outbreaks occurring in India and Bangladesh were caused by direct contact with the virus from bat excretions (saliva or urine) that contaminated raw date palm sap, which is used in making a popular drink in both locations. Once the infection was established in humans, person-to person transmission via infected body fluids and droplets caused additional cases.

Symptoms of Nipah virus disease usually appear within two weeks of exposure to the virus, and most often begin with fever and headache. Some people with Nipah virus disease also have a cough, sore throat, nausea, abdominal pain, or blurred vision early in the course of the disease. Drowsiness, disorientation, and mental confusion tend to appear within a few days of the start of symptoms, and in severe cases, seizures or coma can result within 48 hours of the onset of the disease.



There is no definitive treatment for Nipah virus disease, and supportive measures offer the best alternative for managing the disease. Mechanical ventilation may be necessary, along with hydration, seizure control, prevention of secondary infections, and fever control. The antiviral drug ribavirin has shown benefit in laboratory settings, but its effectiveness in treating humans with Nipah virus disease remains inconclusive. Survivors of Nipah virus disease require monitoring for long-term relapse, along with support for disability and neurological complications including seizures and personality changes.

Public health role and response

In order to contain the initial outbreak of Nipah virus disease, more than one million pigs were culled in Malaysia, resulting in economic hardship for many in the livestock industry. The cull number was likely greater than necessary, as bats were initially not suspected as the reservoir of the disease. Today, surveillance systems in most of Malaysian pig farms are in place to provide an early warning for future outbreaks. Long-term measures to prevent Nipah outbreaks focus on limiting the shared spaces and food resources among bats, livestock, and humans.

A vaccine for Hendra virus, a closely related virus to Nipah that is also capable of causing serious disease and fatalities in humans and other mammals, has been developed in Australia for use in horses. There is evidence that the vaccine could also confer some immunity to Nipah virus disease, offering a potential starting point for formulating a vaccine intended to prevent both Nipah and Hendra disease in humans.


During the initial outbreak of Nipah virus disease in Malaysia and Singapore, the case fatality rate approached 40 percent. Subsequent outbreaks in India and Bangladesh saw the case fatality rates rise to between 70 percent and 100 percent. Relapsing encephalitis occurred among some affected persons in Malaysia almost a year after initial infection, and survivors can experience long-term neurologic dysfunction. Nipah virus disease remains a serious challenge even in the presence of modern supportive care. As many outbreaks occur in areas with less developed medical infrastructure, case fatality rates are likely to remain high in future outbreaks without access to substantial advancements in treatments.

Killing potential animal hosts regardless of their infection status in order to limit the spread of disease.
A disease or pathogen that is normally present in an environment and sparks periodic outbreaks.
Intermediate host—
An animal host that supports some form of a pathogen that becomes more efficient in its ability to infect another species, either through genetic changes, parasite maturity, or an increase in numbers.
Cultivating a single species of plant crop.
A disease-causing organism.
Reservoir host—
An animal or plant host whose systems maintain an infectious organism while unharmed by it, and serve as a source for infection for other species.
A disease that can be transmitted to humans from animals.


Preventing infection with Nipah virus is best achieved by avoiding raw date palm sap and its products, and avoiding contact with bats and pigs when in areas where Nipah virus disease outbreaks occur. Strict barrier infection control precautions protect healthcare workers and limit human-to-human transmission in healthcare settings. Surveillance systems in South Asian pig farms help indicate the presence of disease before large-scale outbreaks occur. As the Nipah virus is labile and easily killed with common detergents, handwashing programs for livestock workers and procedures for washing transport crates and vehicles have been introduced with success. Limiting deforestation and monoculture for palm oil plantations, preserving dedicated habitat for bats, and planning that reduces the interface between bats, human settlement, and commercial agriculture could also help control outbreaks of Nipah virus and other zoonotic diseases.


Unless travelling to an area where Nipah virus disease outbreaks have occurred and also coming in contact with infected humans or pigs, with raw date palm sap, or with infected fruit bats and their saliva or excreta, it is unlikely for a person to contract Nipah virus disease. Nevertheless, symptoms with or without travel history should precipitate a prompt consultation with a physician.



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Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA, United States, 30329, (800) CDC-INFO, CDC-INFO, .

International Society for Infectious Diseases (ISID), 9 Babcock Street, Unit 9, Brookline, MA, United States, 02446, (617) 277-0551,, .

World Health Organization (WHO), Avenue Appia 20, Geneva, Switzerland, CH - 1211 Geneva 27, , .

Brenda W. Lerner, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.