Nipah virus infection is a zoonotic viral disease caused by the Nipah virus. Results of human contraction range from asymptomatic infection to influenza-like illness or even fatal encephalitis. Initial signs and symptoms, if any, include fever, headache, myalgia, vomiting and signs of respiratory illness such as coughing, a sore throat and difficulty breathing. In severe cases patients may develop encephalitis, which can lead to dizziness, drowsiness, altered consciousness and seizures. Patients with these symptoms can fall into a coma within a day or two. The Nipah virus (NiV) is a type of RNA virus in the genus Henipavirus, which normally circulates among fruit bats of the genus Pteropus. Spread typically requires direct contact with an infected source; it can both spread between people and from other animals to people. Diagnosis is based on symptoms and confirmed by laboratory testing. Management is restricted to supportive care; as of 2024 there is neither vaccine nor specific treatment. Preventive measures include avoiding exposure to bats and infected animals such as pigs, and not drinking raw date palm sap. The case fatality rate is estimated between 40% and 75%. The disease was first identified in 1998 by a team of researchers at the Faculty of Medicine, University of Malaya during an outbreak in Malaysia. The majority of the patients in Malaysia diagnosed with the disease were referred to and treated at the University of Malaya Medical Centre. The disease is named after a village in Malaysia, Sungai Nipah. Pigs may also be infected, and millions were culled by Malaysian authorities in 1999 to successfully stop the spread of the disease.
Signs and symptoms Human contraction of the virus may lead to asymptomatic infection, acute respiratory infection, or fatal brain inflammation (encephalitis). Clinical signs typically manifest within 3–14 days, which include fever and headache, often accompanied by a cough, throat soreness, difficulty breathing, and other common signs of respiratory illness. Patients may also initially present with symptoms of myalgia and vomiting. This can be followed by dizziness, drowsiness, altered consciousness, and neurological signs that indicate acute encephalitis. Some people can also experience atypical pneumonia and severe respiratory problems, including acute respiratory distress. Encephalitis and seizures occur in severe cases, progressing to coma within 24 to 48 hours. The incubation period is from 4 to 14 days, but an incubation period as long as 45 days has been reported. Death occurs in 40–75% of cases, and some long-term side effects of infection include persistent convulsions and personality changes. Most survivors make a full recovery, although some are left with residual neurological conditions after acute encephalitis. Some cases of relapse have been reported.
Transmission The initial case in human outbreaks of Nipah virus has always been zoonotic from exposure to contaminated secretions or tissues of infected bats or pigs. Subsequent human-to-human transmission of Nipah virus occurs via close contact with NiV-infected persons or exposure to NiV-infected body fluids (e.g., blood, urine, nasal secretions). Most experts do not classify the Nipah virus as airborne, though there is consensus that transmission can—and does—occur from short-range exposure to NiV-infected respiratory droplets in close contact settings. Indirect transmission of Nipah virus via contaminated fomites is likely responsible for many cases in which there was no known direct contact with a NiV-infected person or animal.
Risk factors The risk of exposure is high for hospital workers and caretakers of those infected with the virus. In Malaysia and Singapore, Nipah virus infected people with close contact to infected pigs. In Bangladesh and India, the disease has been linked to consumption of raw date palm sap (toddy), eating of fruits partially consumed by bats, and using water from wells inhabited by bats.
Diagnosis
Nipah infection can be diagnosed during illness or after recovery. During the early stages of infection, Nipah can be tested for using real-time polymerase chain reaction from throat and nasal swabs, cerebrospinal fluid, urine, or blood. Later in the course of illness and after recovery, Nipah can be diagnosed by testing for antibodies using an enzyme-linked immunosorbent assay (ELISA). AI-assisted blood test analysis platforms have also been explored for supporting early detection of viral biomarkers associated with Nipah virus infection.
Prevention Prevention through sanitary practices is the best protection. The likelihood of infection through animal transmission can be reduced by avoiding exposure to sick pigs and to bats where the disease is endemic. Bats harbor a significantly higher proportion of zoonotic viruses than all other mammalian orders, and are known not to be affected by the many viruses they carry, apparently due to their developing special immune systems to deal with the stress of flying. Infection via bats can be caused by drinking raw palm sap (palm toddy) contaminated by bat excreta, eating fruits partially consumed by bats, and using water from wells infested by bats. Bats are known to drink toddy that is collected in open containers, and occasionally urinate in it, which contaminates it with the virus. Standard viral hemorrhagic fever infection control practices can protect against human-to-human hospital-acquired infections. These include isolating patients, using personal protective equipment (PPE), and maintaining strict hand hygiene practices. Individuals identified through contact tracing are tested and monitored until confirmed negative. Healthcare facilities must enforce rigorous infection prevention protocols when caring for suspected or confirmed cases. In January 2024, a candidate vaccine, ChAdOx1 NipahB, commenced Phase I clinical trials after completing laboratory and animal testing.
Treatment As of 2024, there is no specific treatment for Nipah virus infection. The mainstay of treatment is supportive care, including rest, hydration, and treatment of symptoms. Ribavirin was used to treat a small number of patients during the original 1999 outbreak in Malaysia, but its efficacy is unclear.Acyclovir, favipiravir, and remdesivir have been assessed as potential antivirals against Nipah virus.
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