Indian authorities said this week that they are working to contain an outbreak of Nipah, a rare virus that is transmitted from animals to humans and causes high fever and a high mortality rate.
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Here’s what we know so far.
What is the Nipah virus?
The first outbreak of Nipah was recorded in 1998 after the virus spread among pig farmers in Malaysia. The virus is named after the village in the Southeast Asian country where it was discovered.
Outbreaks of this virus are rare, but Nipah has been listed by the World Health Organization (WHO) – along with Ebola, Zika and Covid-19 – as one of several diseases that deserve priority research because of their potential to cause a global epidemic. Nipah is usually transmitted to humans through animals or contaminated food, but can also be transmitted directly between humans.
Fruit bats are the natural vectors of the virus and have been identified as the most likely cause of subsequent outbreaks.
Symptoms include high fever, vomiting and respiratory infections, but severe cases can be characterized by seizures and encephalitis leading to coma.
There is no vaccine against the Nipah virus. According to the WHO, the mortality rate of patients is between 40 and 75%.
What about previous epidemics?
The first Nipah outbreak in Malaysia killed more than 100 people and killed a million pigs to contain the virus.
It has also spread to Singapore, where there have been 11 cases and one death among slaughterhouse workers who came into contact with pigs imported from Malaysia.
Since then, the disease has been reported primarily in Bangladesh and India, with both countries recording their first outbreaks in 2001. The hardest hit in recent years has been Bangladesh, where more than 100 people have died from Nipah since 2001.
Two 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 more confirmed cases since last month. The authorities have closed certain schools and carried out large-scale testing campaigns.
This latest Nipah outbreak represents the fourth wave in Kerala in five years. When it first emerged in 2018, the virus killed 17 people.
Increasing transmission from animals to humans?
Zoonoses – diseases that can be transmitted from animals to humans – appeared thousands of years ago and have multiplied in the last 20 to 30 years.
The development of international travel enabled them to spread more quickly. By occupying ever larger areas of the planet, humans are also contributing to the disruption of ecosystems and increasing the likelihood of random virus mutations that can be transmitted to humans, experts point out.
Industrial agriculture increases the risk of pathogens spreading between animals, while deforestation increases contact between wildlife, domestic animals and people.
As species mix more, they will transmit their viruses more, which will encourage the emergence of new diseases that may be transmissible to humans. Climate change will push many animals to flee their ecosystems for more habitable areas, a study published in the journal Nature warned in 2022.
It was estimated in 2018 that there are 1.7 million unknown viruses in mammals and birds, of which 540,000 to 850,000 can infect humans.