Story highlights
Nipah virus spreads from animals to people and among humans
Infection can cause fatal encephalitis, inflammation of the brain
A little-known virus causing deaths in a southern Indian state has become a global cause for concern seemingly overnight.
Nipah virus has killed as many as three-quarters of patients during previous outbreaks. It is a zoonotic virus, meaning it is transmitted from animals to humans.
Nipah is also considered an “emerging” virus because its discovery occurred relatively recently: in the past two decades. Though there have been only a few outbreaks, Nipah is considered a public health threat because it can infect a wide range of animals while leading to severe disease and death in people, according to the World Health Organization.
Infection with Nipah virus can cause no symptoms, or it can cause fatal encephalitis (inflammation of the brain), with a range of possible illnesses between those two extremes.
The natural host is a particular family of bats, Pteropodidae, which can spread severe disease to farm animals including pigs, resulting in substantial economic losses.
The name comes from Sungai Nipah, a village in the Malaysian peninsula where the virus was identified after farmers became sick in 1998 and 1999.
How is it transmitted?
In past outbreaks, human infections are believed to have resulted from direct contact with sick pigs, including throat and nasal secretions or contaminated tissues, according to the US Centers for Disease Control and Prevention.
Eating fruits or fruit products (such as raw date palm juice) contaminated with urine or saliva from infected fruit bats is also believed to have caused human infections.
Nipah virus can also spread directly from person to person, with family members or medical staff most at risk since transmission requires very close contact with the ill or deceased.
What are the signs of illness?
Between four and 14 days may elapse between the infection and a patient’s first symptoms. However, a 45-day incubation period has been reported, according to WHO.
Commonly, once infected, a person develops flu-like symptoms of fever, headaches, muscle pain, vomiting and sore throat. Sometimes, this is followed by dizziness, drowsiness, altered consciousness and signs of encephalitis. Some patients will develop severe respiratory problems, including pneumonia or acute respiratory distress that would require mechanical assistance to breathe.
In the most severe cases, encephalitis and seizures will progress to coma within 24 to 48 hours.
How deadly is it?
Scientists estimate the fatality rate at 40% to 75%, varying by outbreak. Most people who survive acute encephalitis brought on by Nipah virus make a full recovery, but some former patients report long-term neurologic conditions. About 20% of patients are left with seizure disorder and personality changes, while a small number relapse.
How is it treated?
There are no drugs or vaccines to specifically treat or prevent Nipah virus infection.
Supportive care is the recommended treatment, so health care workers and caretakers do their best to provide symptom relief, such as trying to bring down a fever by cooling a patient.
Where is it?
Outbreaks have occurred in Malaysia, Singapore, Bangladesh and India.
Patients are believed to have either had contact with animals, consumed raw date palm juice or had contact with infected people. Other regions and countries that are home to the related species of bat may also be at risk for Nipah virus infections, including Cambodia, Thailand, Indonesia, Madagascar, Ghana and the Philippines, according to WHO.
Join the conversation
How common is it?
Nipah virus is very rare. From 1998 to 2015, WHO reported more than 600 cases, with subsequent high-fatality outbreaks occurring in India and Bangladesh, though the total number of people affected remains unknown.