Outbreak status and risk assessment of Nipah virus infection

Japan Institute for Health Security

January 30, 2026

This document provides information based on official documents published by national and international health and research institutions. Therefore, it does not include information announced at press conferences, etc. As investigations by domestic and international health organizations and researchers continue, the information may have been significantly updated since the date of publication of this document. Please refer to the most recent updates for the latest information.

1.Overview

Nipah virus is a negative-sense, single-stranded RNA virus with an envelope belonging to the genus Henipavirus of the Paramyxoviridae family. Flying fox (fruit bats) that live in tropical and subtropical regions of South Asia and East Asia are the natural hosts. The virus is transmitted to humans through direct contact with fruit bats; ingestion of fruits, vegetables or unheated processed products contaminated with fruit bat body fluids; contact with pigs or horses infected via fruit bats; and close contact with infected people at home or in medical institutions.

After an incubation period of about 4-14 days, patients typically develop non-specific symptoms such as fever, headache, and muscle pain; as the illness progresses, neurological symptoms such as dizziness, drowsiness, and altered consciousness may appear. Reports also indicate that respiratory symptoms may develop. There have been reports of the use of multiple antiviral drugs, but treatments and vaccines with established efficacy and safety are not available. The case fatality rate is reported to be between 40% and 75% (WHO, 2026). However, case ascertainment differs across settings because of variation in surveillance capability and medical systems; mild cases may be missed, which can overestimate the case fatality rate.

The WHO has listed Nipah virus infection as a priority disease with pandemic potential, warranting prioritization for research and development because of the lack of vaccines and treatments, the high case fatality rate, and the potential for human-to-human transmission (WHO, 2024).

2. Epidemiological situation of Nipah virus infection

Nipah virus infection was first reported in Malaysia and Singapore in 1998-1999. In this epidemic, the virus was transmitted from fruit bats to pigs, and it is thought that transmission of infection to humans occurred through an epidemic of respiratory infections in pigs (Chua, 2003).

Since then, outbreaks have been reported in the Philippines, Bangladesh, and India, and in Bangladesh and India in particular, there have been reports of outbreaks every year since 2001. Unlike Malaysia, Bangladesh and India have reported many cases of infection from oral ingestion of date sap, fruit, and processed products contaminated with the body fluids of fruit bats. In addition, close contact with patients at home and healthcare-associated infections resulting from patient care and examination at medical institutions have also been reported. On the other hand, large-scale community transmission via human-to-human transmission has not been reported so far. In addition, fruit bats with Nipah virus antibodies have been reported, including countries where no cases have been reported in humans, and it is thought that there is a risk of outbreak depending on the local situation in areas where fruit bats live.

In Japan, there have been no reports of patients with Nipah virus infection. In addition, the area where fruit bats live in Japan is limited to the Ogasawara Islands and the Nansei Islands, and there are no reports of fruit bats with Nipah virus.

3.Risk assessment

• Nipah virus infection is endemic in South and Southeast Asia through contact with infected animals such as fruit bats and pigs, ingestion of fruits and vegetables such as dates and their unheated processed products contaminated with their bodily fluids, and contact with patients and their bodily fluids at home and in medical institutions. Therefore, the risk of infection in South and Southeast Asian countries is high when these risk behaviors are involved.
• In recent years, outbreaks have been reported in South Asia, but all of them have been limited to small-scale outbreaks associated with the risk behaviors mentioned above, and no human-to-human transmission has been reported in large communities, so the risk of infection with Nipah virus among travelers and locals without risk behaviors is low.
• The habitat area of fruit bats, known as the host of Nipah virus, is limited to some islands in Japan, and there are no reports of bats with Nipah virus in Japan, so the risk of Nipah virus infection in Japan is low.
• When imported cases occur, if appropriate infection control measures are not taken, household infections and healthcare-related infections may occur in Japan. However, sustained community transmission in Japan is unlikely; Nipah virus is not readily transmitted through casual contact in daily life.

4.Recommended action

• When traveling to areas where Nipah virus infection is endemic, the following precautions are recommended.

1. 1. Basic infection prevention measures include hand hygiene such as hand washing with soap and water, using alcohol disinfectant, wearing masks, and cough etiquette.
   2. Avoid direct contact with bats and pigs, and avoid touching or eating raw unwashed fruits and sap such as dates.
   3. Avoid contact with patients with Nipah virus infection and people who are unwell and suspected of having Nipah virus infection as much as possible, and if they do come into contact, avoid direct contact with patients and their bodily fluids using gloves and other means to prevent infection and implement basic infection prevention measures such as hand hygiene.
   4. If any of the above risk behaviors occur during travel and symptoms suggestive of Nipah virus infection, including fever, headache, dizziness, or neurological symptoms, develop during travel or after return, prompt medical evaluation is recommended. In such cases, travel history and relevant local exposures should be clearly communicated to healthcare providers.

• Travelers with risky behavior in Nipah virus endemic areas may develop Nipah virus infection while abroad. When examining patients with severe infectious diseases such as acute encephalitis and acute respiratory infections of unknown cause, medical professionals need to differentiate Nipah virus infection and take appropriate measures, including infection control measures. For details on clinical response, please refer to Henipavirus Infection Clinical Practice Guidelines 2024.

Related information

Japan Institute for Health Security, National Institute of Infectious Diseases. Nipah virus infection (Japanese language page)

Japan Institute for Health Security, National Institute of Infectious Diseases. Nipah Virus Infection and Hendra Virus Infection Testing Manual (Version 1.2) (Japanese language page)

Japan Institute for Health Security, National Center for Global Health and Medicine, Disease Control and Prevention Center
Henipavirus Infection Clinical Practice Guidelines 2024 (external link, Japanese language page)

Ministry of Health, Labour and Welfare Quarantine Station　FORTH (external link, Japanese language page)

References

• Chua, K.B., Nipah virus outbreak in Malaysia. J Clin Virol, 2003. 26(3): p. 265-75.
• WHO, Pathogens Prioritization, June 2024. https://cdn.who.int/media/docs/default-source/consultation-rdb/prioritization-pathogens-v6final.pdf?sfvrsn=c98effa7_9&download=true
• WHO, Nipah Virus Infection, accessed 30 Jan 2026. https://www.who.int/health-topics/nipah-virus-infection#tab=tab_1.

 

Creation

Japan Institute for Health Security Bureau of Health Security and Management

Department of Intelligence and Emergency Operations

Department of Infectious Disease Epidemiology

Department of Infectious Disease Clinical Policy

National Institute of Infectious Diseases

Center for Emergency Preparedness and Response

Department of Veterinary Science

Center for Public Health Action in Applied Epidemiology

Field Epidemiology Training Program (FETP-J)

Department of Infectious Disease Surveillance

National Center for Global Health and Medicine

　 Disease Control and Prevention Center