What is Nipah virus? Kerala starts mass testing after outbreak in India

Indian authorities have instituted mass testing to halt the spread of the deadly Nipah virus, which has killed two people in the southern state of Kerala.

Public gatherings were curbed and some schools were shut last week, officials said on Thursday. It is the fourth outbreak in the region since 2018.

Nipah is a rare but serious bat-borne virus that can cause fever, vomiting and respiratory infections in humans. Severe cases can involve seizures and encephalitis – inflammation of the brain – and result in a coma.

The virus has a fatality rate between 40-75%, according to the World Health Organization (WHO). It has no known vaccine, and the usual treatment is to provide supportive care.

What is the Nipah virus?

The first Nipah outbreak was recorded in 1998 after the virus spread among pig farmers in Malaysia and Singapore. The virus is named after the village where it was discovered.

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.

Flying foxes are the natural carriers of the virus. “It’s carried by fruit bats who sit in the tops of trees,” said Joanne Macdonald, an associate professor of molecular engineering at the University of the Sunshine Coast. “They can urinate and contaminate fruit, and when people eat that they get the virus and then they get sick.”

“Once you get it, [the only treatments are] rest, hydration, treatment of symptoms.”

Scientists fear a mutated, highly transmissible strain will emerge from bats. Outbreaks are rare but Nipah has been listed by the WHO as one of several diseases deserving of priority research for their potential to cause a global epidemic, alongside Ebola, Zika and Covid-19.

Nipah is a type of Henipavirus, and is related to Hendra virus, which was first discovered in Australia and has caused deaths in humans and horses.

What has happened during previous outbreaks?

The first Nipah outbreak in 1998 infected nearly 300 people in Malaysia, killing more than 100, and prompted the culling of one million pigs in an effort to contain the virus.

It also spread to Singapore, with 11 cases and one death among slaughterhouse workers who came into contact with pigs imported from Malaysia.

Since then, the disease has mainly been recorded in Bangladesh and India, with both countries reporting their first outbreaks in 2001. Bangladesh has borne the brunt in recent years, with more than 100 people dying of Nipah since 2001.

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

Two early outbreaks in India killed more than 50 people before they were brought under control.

The southern state of Kerala has recorded two deaths from Nipah and four other confirmed cases since last month. This marks Kerala’s fourth recorded outbreak of Nipah in five years, after other instances in 2018, 2019 and 2021.

The state has managed to stamp out previous outbreaks within a matter of weeks through widespread testing and strict isolation of those in contact with patients.

Are animal-to-human viruses becoming more frequent?

Zoonotic diseases – those that can be transmitted from animals to humans – have multiplied over the past 20 to 30 years.

Industrial farming increases the risk of pathogens spreading between animals while deforestation heightens contact between wildlife, domestic animals and humans.

Scientists have warned that the climate crisis is increasing the risk of “zoonotic spillover” events, with 15,000 instances of viruses jumping between species predicted over the next 50 years.