Explained: What is Nipah and why is the deadly virus flaring up again

It’s the third time in five years that the brain-damaging virus, which can spread from bats and pigs to humans, has surfaced in the Kozhikode district of Kerala. In a 2018 outbreak, 21 people died before it was contained. The virus has previously been detected in countries including Singapore and Malaysia. Here’s what you need to know about it:

What is Nipah virus?

Nipah is a zoonotic virus — meaning it can be transmitted from animals to humans — which can cause a severe respiratory infection and attack the brain, according to the World Health Organization. It was first detected in 1999 during an outbreak among Malaysian pig farmers, and was also found in Singapore. While no new infections have occurred in either location, there have been periodic flare-ups in Bangladesh and India since 2001.

How is Nipah virus transmitted?

The Malaysian outbreak is believed to have been caused by the virus spreading from infected pigs to humans. But in India and Bangladesh, the most likely transmission path is thought to be from the consumption of fruit products — such as date palm sap — contaminated by the urine or saliva of infected fruit bats, according to the WHO. The health organization said a high percentage of subsequent outbreaks likely involved human-to-human transmission.

What are the symptoms of Nipah infections?

Symptoms usually begin with a fever and headache, often accompanied by signs of respiratory illness like a cough or sore throat, according to the US Centers for Disease Control and Prevention. They may appear any time within two weeks of exposure to the virus. The infection can worsen, leading to disorientation, seizures and encephalitis — a swelling of the brain — which may put patients into a coma within 24 to 48 hours.

How dangerous is it?

India is right to be concerned. An estimated 40% to 75% of infected patients die from the virus, with the mortality rate varying from outbreak to outbreak.

How is Nipah virus treated?

There are no Nipah vaccines available for humans or animals, nor are there any effective treatments other than supportive care. Researchers are currently developing monoclonal antibodies — immunotherapeutic drugs that would directly fight the virus — but no licensed treatments are yet available, according to the CDC. Compassionate use of experimental compounds have been offered previously, and local media are reporting that India is working to make monoclonal antibodies available. In the case of the Kerala outbreak, authorities are using patient contact tracing in a bid to contain the spread of the virus.

Which other countries have reported Nipah?

So far the virus has been confined to Asian countries: India, Bangladesh, Singapore, Malaysia and the Philippines

Are animal-human viral transmissions on the rise?

Scientists have suggested that factors such as climate change and deforestation are increasing the risk of animal-human crossover infections. In the case of the Nipah outbreak in Malaysia, “agricultural intensification” was thought to have created a pathway for the virus to spread from fruitbats to pigs and then to humans. Zoonosis is common, accounting for more than six of out of every 10 known infectious diseases in people, according to the CDC. Most of the time the infections cause limited disease, dying out without having a major impact. However, in the aftermath of Covid-19, more tracking systems now are in place and picking up novel pathogens.