Nipah: What do we know about virus spreading in India's Kerala?

India's southern state of Kerala shut some schools and offices this week as officials raced to halt the spread of the deadly Nipah virus, after it killed two people in the fourth outbreak since 2018.

Here is what we know about the virus:

WHERE DID THE VIRUS COME FROM?

The Nipah virus was first identified in 1998 during an outbreak of illness among pig farmers in Malaysia and Singapore.

It is able to infect humans directly through contact with the bodily fluids of infected bats and pigs, with some documented cases of transmission among humans.

Scientists suspect Nipah has existed among flying foxes for millennia and fear a mutated, highly transmissible strain will emerge from bats.

WHAT ARE THE SYMPTOMS AND HOW IS IT TREATED?

There are no vaccines to prevent or cure the infection, which has a mortality rate of between about 70%. The usual treatment is to provide supportive care.

Infected people initially develop symptoms that include fever, respiratory distress, headaches, and vomiting, the World Health Organization (WHO) says. Encephalitis and seizures can also occur in severe cases, leading to coma.

The virus is on the WHO's research and development list of pathogens with epidemic potential.

WHERE WERE THE EARLIER OUTBREAKS?

The 1998 outbreak in Malaysia and Singapore killed more than 100 people and infected nearly 300. Since then, it has spread thousands of miles, killing between 72% and 86% of those infected.

More than 600 cases of Nipah virus human infections were reported between 1998 to 2015, WHO data shows.

A 2001 outbreak in India and two more in Bangladesh killed 62 of 91 people infected.

In 2018, an outbreak in Kerala claimed 21 lives, with other outbreaks in 2019 and 2021.

Parts of Kerala are among those most at risk globally for outbreaks of bat viruses, a Reuters investigation showed in May.