The World Health Organization reported two cases of a rare virus in an eastern Indian state on Thursday.
The virus — called Nipah — kills more than half of the people it infects. The Nipah virus, named after the village in Malaysia where the first known patient lived, is part of the same family of viruses as measles. However, it is not as infectious as measles, but it is far more deadly.
How is it transmitted?
Nipah is a zoonotic virus, which means it can be transmitted from animals to humans. Most commonly, it occurs through direct contact with an infected pig or bat, according to the US Centers for Disease Control and Prevention. Eating fruit or fruit products – such as raw date palm juice – contaminated with urine or saliva from infected fruit bats also contributes to the spread.
It can also spread directly from person to person. Transmission, however, occurs through very close contact with the infected individual.
What are the signs of illness?
It can take between four and 14 days for symptoms to appear after a person is infected, according to the WHO, and asymptomatic cases are rare.
The first signs of infection are non-specific and include flu-like symptoms such as fever, headache, muscle aches, vomiting and sore throat. In about two-thirds of patients, the disease progresses rapidly, and coma may strike within five to seven days. Some infections also lead to respiratory symptoms such as coughing and abnormal chest X-rays.
Most patients show changes in the fluid that surrounds the brain, which are commonly seen in other viral infections of the brain. Changes caused by tissue death can be seen on brain imaging, and the brain’s electrical activity predicts the severity of the disease.
How dangerous is it?
The virus is classified by the CDC as biosecurity level four — the highest category, with the most dangerous pathogens like Ebola — and has the potential to serve as an agent for bioterrorism.
Although there have been only a few outbreaks, Nipah is considered a public health threat due to its high fatality rate, potential for human-to-human transmission, ability to cause outbreaks and lack of approved vaccines or treatment.
In severe cases, the virus can attack parts of the brain that control basic life functions such as eye movement, heart rate and blood pressure, causing permanent damage.
Survivors often experience fatigue and changes in the way their nervous system works. These effects often persist for years.
How is it diagnosed?
Testing is often done using a blood sample to detect and quantify specific proteins.
How is it treated?
There is no vaccine or medicine specifically for Nipah. Doctors provide supportive care, and patients who develop severe neurological symptoms may need help breathing.
A drug called ribavirin — which is approved for use with other drugs to treat chronic hepatitis C — may offer some benefit, although results are mixed.
The result is that doctors focus on prevention by reducing the risk of animal-to-human transmission and implementing infection control measures when working with infected people.
Where do outbreaks occur?
Nipah outbreaks occur almost every year in parts of Asia, most often in Bangladesh, India, Malaysia, the Philippines and Singapore, with Bangladesh recording the highest number of infections. This is because the fruit bats that transmit the virus — among the largest bats in the world — are native to these regions.
The virus typically spreads from December to May, during the bat breeding season and the date palm shell harvesting season.
Nipah virus has also been found in bats from China, Cambodia, Thailand, Madagascar and Ghana. A case of Nipah has never been reported in the United States.
How common is it?
It is very rare. As of 2024, approximately 754 cases have been reported globally, although that figure is probably an underestimate.
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