- Related Topics:
- flying fox
- Nipah virus disease
- On the Web:
- Cambridge University Press - Cambridge Core - Nipah virus infection: A review (Oct. 17, 2026)
Nipah virus
What is Nipah virus?
How is Nipah virus transmitted?
Do bats get sick from Nipah virus?
What are the symptoms of Nipah virus disease?
How can Nipah virus infection be prevented?
Nipah virus, bat-borne infectious agent that causes a febrile illness in humans. Known as Nipah virus disease, this condition can progress to severe respiratory distress and potentially fatal encephalitis (brain inflammation), with a fatality rate as high as 75 percent.
Outbreaks of Nipah virus disease are sporadic and have been limited to South and Southeast Asia. The virus is named for the Malaysian village of Kampung Sungai Nipah, where the first human cases were identified in 1998–99. No vaccines or treatments are available for Nipah virus disease.
Viral structure and pathogenesis
Evidence indicates that some species of pteropid bats handle viruses differently from most animals. For example, when exposed to Nipah virus, fruit bats (Pteropus) do not significantly increase their type I interferon (IFN-I) response, which is a first line of defense against invading pathogens such as viruses. Instead, their IFN-I system is always active at a constant level, continuously triggering certain interferon-stimulated genes that help control viral replication.
Experts also suspect that when infection occurs, bats quickly activate their type III interferon (IFN-III) response, which produces antiviral cytokines, while retaining steady IFN-I activity. This balanced innate immune response stops the virus from multiplying without fully eliminating it and prevents the body from mounting an excessive reaction to the pathogen. These mechanisms collectively allow bats to carry viruses without experiencing symptoms of infection.
Nipah virus (NiV) belongs to the genus Henipavirus, which is classified in the family Paramyxoviridae. Similar to other members of this family, Nipah virus is made of single-stranded, negative-sense RNA. Its genetic material and replicative complex—composed of nucleocapsid protein, phosphoprotein, and RNA polymerase—are enclosed within a matrix protein shell and a lipid bilayer. The lipid bilayer is covered with spikelike attachment and fusion glycoproteins that bind to ephrin-B2 and ephrin-B3 receptors on host cells, enabling viral entry. These receptors are found on epithelial cells, endothelial cells (those that line blood vessels), and neurons across many mammalian species, making a wide range of hosts susceptible to infection.
" height="20" alt="HEW Logo">
Although research is ongoing, it is generally thought that Nipah virus first infects the epithelial cells of the respiratory tract. It causes nearby host cells to fuse into one large, multinucleated cell (a syncytium). When this cell breaks down, the virus is released into the bloodstream. From the lungs the virus can spread to the blood vessels and bloodstream, and from the olfactory epithelium it can reach the brain through the olfactory nerve. Other vital organs such as the heart, kidneys, and spleen are also affected. Nonstructural proteins synthesized by the virus affect host innate immune cells and impair immune responses, which contribute to disease development. In response to viral replication in the central nervous system, inflammatory cytokines are produced. Their production has been linked to the disruption of the blood-brain barrier and the development of neurological symptoms.
Reservoirs and transmission
Fruit bats (Pteropus; also called flying foxes) are the natural reservoir hosts of Nipah virus. In infected bats the virus is present in feces and various bodily fluids, including urine, saliva, blood, and birthing fluids. Contact with these substances is the primary route of Nipah virus transmission to other species. For example, transmission can occur through the consumption of fruits that were bitten by an infected bat and thus became contaminated with the virus. The raw sap of date palm plants, which is widely consumed in Bangladesh and the state of West Bengal in India, as well as the naturally fermented liquor derived from the sap (called tari), can also be contaminated by bats and are additional sources of viral transmission.
Although fruit bats are reservoir hosts, they do not develop symptoms of Nipah virus infection owing to their specialized immune systems, which tolerate the virus. Intermediate hosts for Nipah virus include pigs and horses, which develop symptoms and are a source of infection for humans. Other animals, including dogs, cats, hamsters, ferrets, guinea pigs, squirrel monkeys, and African green monkeys, have also shown susceptibility to infection, which makes the virus a major public health concern. An infected person can spread the disease through their bodily fluids. The possibility of airborne transmission through virus-laden aerosols has not been confirmed.
Nipah virus disease outbreaks
The first human cases of Nipah virus infection were reported among pig farmers in Malaysia in 1998–99. Infection is thought to have spread from contact with the contaminated tissues and bodily fluids of infected pigs. The disease spread to Singapore in 1999, when infected pigs were imported from Malaysia. About 300 people were infected during this outbreak, and more than a third of them died. Beginning in 2001, outbreaks have occurred almost every year in Bangladesh. India also reported cases of the virus and its disease for the first time in 2001, with subsequent outbreaks reported periodically from the states of Kerala and West Bengal. In 2014 a Nipah virus outbreak in the Philippines was linked to contact with and consumption of meat from infected horses.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
Symptoms, detection, treatment, and precaution
- Nipah virus is classified by the U.S. Centers for Disease Control and Prevention as a Category C bioterrorism agent—the lowest of the three bioterrorism threat categories.
- The virus must be handled exclusively in biosafety level 4 (BSL-4) facilities that provide the highest levels of biosafety.
- It remains viable in raw date palm sap for seven days at 22 °C (71.6 °F).
- It can be rendered inactive by heating at 100 °C (212 °F) for at least 15 minutes, using soaps, detergents, and sodium hypochlorite, and irradiating with ultraviolet light.
- Washing, peeling, and cooking fruits thoroughly before consumption can reduce the risk of contamination.
- Two strains of Nipah virus are recognized—Malaysia (NiV-M) and Bangladesh (NiV-B)—of which the Bangladesh strain has higher pathogenicity.
- As of January 2026 more than 400 people have died of Nipah virus infection worldwide.
People infected with Nipah virus may be asymptomatic or may present nonspecific symptoms, including fever, headache, body aches, nausea, vomiting, and sore throat. Some patients may experience extreme breathing difficulty. Patients may also report dizziness, lethargy, and confusion, which are signs of encephalitis. Symptoms usually appear within 4 to 14 days of infection. In severe cases encephalitis and seizures are followed by coma within 24 to 48 hours. Although some patients recover, death occurs in 40 to 75 percent of cases. About 20 percent of patients who recover from acute encephalitis report residual neurological symptoms, including fatigue, seizures, and changes in behavior. Relapse has been reported in some patients, and encephalitis may develop later.
The nonspecific nature of the symptoms makes Nipah virus disease difficult to diagnose. Physicians rely on clinical features during the acute phase of the disease, as well as detection of viral RNA in bodily fluids using real-time polymerase chain reaction and detection of antibodies using enzyme-linked immunosorbent assay.
In the absence of approved medicines or vaccines, the treatment of Nipah virus infection is limited to providing supportive care for respiratory and neurological complications. Several experimental therapies, including the monoclonal antibody m102.4 and such antivirals as remdesivir and ribavirin, have been used in some cases. Newer classes of drugs, such as fusion-inhibitory peptides, are being developed for the treatment of Nipah virus disease. To reduce the risk of Nipah virus infection, the Centers for Disease Control and Prevention recommends regular handwashing with soap and water; avoiding contact with bats, their roosts, and bat-contaminated objects (including food); and avoiding contact with Nipah-infected people or animals (such as pigs) and their bodily fluids.