April 23, 2026 Author : Saraiva da Cunha (infectious diseases) Human Nipah virus infection is a rare disease . It is caused by a virus that can be transmitted from animals to humans. The natural reservoir of this virus is some fruit bats. Domestic species, such as pigs and horses, can be infected, have severe illness, and transmit the virus to humans. In humans, infection can be severe and has a high mortality rate. Documented cases to date have been concentrated in five countries: Malaysia, Singapore, Bangladesh, India, and the Philippines. The Nipah virus is considered a priority microorganism and the infection an emerging disease due to the number of possible host species, high human mortality rate, ability to be transmitted between species and within the same species, and absence of treatments or vaccines. This virus is thus considered a potential cause of a pandemic and, therefore, since its identification, it has been monitored by international health authorities. Currently, the World Health Organization considers the risk of dissemination low, but active surveillance is maintained. What is the Nipah virus? The Nipah virus belongs to the genus Henipavirus , of the family Paramyxoviridae . It was identified during an outbreak of viral encephalitis affecting several people who had contact with pigs in Malaysia and Singapore in 1998-1999. The natural reservoirs of the Nipah virus are fruit bats of the family Pteropodidae , which exist in some coastal regions and islands of the Indian Ocean, India, Southwest Asia, and Australia. These bats can carry the virus without showing signs of illness, but no cases of human disease have been identified in all regions where they exist. Other animal species, including livestock, such as pigs, can be intermediate hosts of the virus and be the origin of human infection , as happened in the first outbreak of Nipah virus infection. How is the Nipah virus transmitted? Human infection can occur after virus transmission: From animals to humans , resulting from human exposure to secretions from bats or other infected animals, when these come into contact with the mouth, nose, or eyes (mucous membranes), or with wounds on the skin. This transmission from animals to humans makes Nipah virus infection a zoonosis. Through the consumption of contaminated food , particularly the fruits or sap of some palm species where bats feed and which they contaminate with their saliva or urine. Between people , through exposure to respiratory secretions or other body fluids. This form of infection is not very efficient and has been documented in situations of very close contact, such as caregivers of sick people. The first outbreak of Nipah virus infection The first outbreak of human infection with the Nipah virus is believed to have been a consequence of some local agricultural practices in Malaysia that reduced the habitat and food availability for bats . These bats would then have expanded their habitat to search for food in areas near pig farms. The pigs became infected through contact with bat secretions and developed a respiratory infection that spread rapidly among the animals and allowed for intense replication of the virus. The high viral load in the respiratory secretions of sick pigs significantly increased the risk of infection for people in close contact. An outbreak of human infection, with encephalitis, then occurred among pig farm workers and professionals involved in the transport and slaughter of animals. The mortality rate reached almost 40%. Initially thought to be Japanese encephalitis, a disease that is transmitted by mosquitoes, several targeted measures were taken, without success. About six months after the first cases of human illness, in March 1999, a new virus was isolated, designated Nipah virus in reference to the name of the place where the patient from whom the virus was isolated lived and identified as the cause of the disease. With the discovery of this new virus and its transmission, the strategy for containing, monitoring, and preventing the disease was altered , and measures such as restrictions on animal movement, sanitary slaughter of animals from farms with identified cases, isolation and disinfection of farms, restrictions on the marketing of potentially suspect meats, among others, were implemented, allowing the outbreak to end in about two months . Since the first outbreak in Malaysia and Singapore, other smaller outbreaks have been recorded in these and other Southeast Asian countries, such as Bangladesh and India, where cases have already been identified in 2026. In the most recent outbreaks, the role of pigs has been much less relevant. Most cases are related to transmission from bats and the consumption of contaminated fruits and palm sap. Incubation period, symptoms, and treatment of Nipah virus infection After infection, the incubation period varies on average from 4 to 14 days but can reach 45 days. There may be asymptomatic infections, but most people develop symptoms, initially nonspecific , such as: Fever; Cough; Headache, sore throat, muscle pain; Nausea and vomiting. The virus affects the respiratory and central nervous systems, and in many cases, the infection progresses rapidly with complications, mainly encephalitis and symptoms such as confusion, drowsiness, seizures, altered state of consciousness, and respiratory distress. The severity of the complications and the speed of progression can result in coma and death within 24 to 48 hours. One in five people who recover have permanent neurological sequelae. Definitive diagnosis of Nipah virus infection is only possible with laboratory confirmation because the symptoms are common to many other diseases. Currently, there is no treatment or vaccine against the Nipah virus , although antiviral drugs and monoclonal antibodies are in clinical trials. Treatment is based on supportive care . The mortality rate of Nipah virus infection is estimated to be between 40% and 75%. Prevention of Nipah virus infection For populations and visitors to at-risk areas, the main preventive measures include: Avoid eating dates or wash and peel them well before eating; Do not ingest raw date palm sap; Avoid proximity to bats and their habitats and other sick animals; Use protective clothing and other appropriate protective measures in areas and hours with a higher risk of the presence of bats, animals, or sick people. References European Centre for Disease Prevention and Control (ECDC). Nipah virus disease . Hassan MZ, Ibrahim SK, Harriss E, Horby P, Olliaro P, Rojek A. Interpreting the natural history and pathogenesis of Nipah virus disease through clinical data, to inform clinical trial design: a systematic review. Lancet Microbe 2026:101295. World Health Organization. Nipah virus . Atualizado 2026. Meet the infectious diseases clinical team from Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
