In 1998, with no explanation or signal of danger, a fearsome disease took off in Malaysia. Pigs died in large numbers and then men slaughtering infected animals also fell ill. They passed it to their families at home. Nearly half of those who got sick died.
It was not Ebola – it was a virus that became known as Nipah, after the Malaysian town of Kampung Sungai Nipah where it was first identified. But there are resemblances to Ebola in the way the disease suddenly emerged from the animal world and then spread between humans, causing a threat to life that caught the medical and scientific world off-guard.
The story of the outbreak of Nipah in Malaysia was told – and embellished – in the 2011 film Contagion, starring amongst others, Kate Winslet, Gwynneth Paltrow and Matt Damon. There, the disease became a global pandemic, killing 26 million people.
In reality, the death toll from Nipah in Malaysia and Singapore, where it had spread, was 105 out of 265 cases, but could have been much worse had it been more easily transmitted. It also caused the collapse of the $1bn pig industry. The disease seemed to come from nowhere, but as with other such viruses, the emergence and spread was caused by a cocktail of human behaviour and environmental change.
The virus is endemic in fruit bats – also known to carry Ebola virus. The bats were on the move, leaving rainforests where slash-and-burn logging was causing massive haze, shutting out sunlight and preventing the fruit they ate from growing. Drought caused by El Niño made things worse.
Large numbers of bats were later seen in the orchards around the pig farms of northwest Malaysia. The virus from their saliva was in the half-eaten fruit they dropped – which was devoured by the pigs.
The Malaysian outbreak was finally stopped by mass culling of pigs in May 1999. But since then there have been regular Nipah outbreaks in Bangladesh, where transmission occurs directly from fruit bats to humans.
“We know how it happens,” said Professor John Clemens, executive director of the International Centre for Diarrhoeal Disease Research, Bangladesh. “The fact that it has established itself as an endemic focus in Bangladesh with regular, albeit infrequent, transmission to man suggests that it could cause broader problems for humanity at large. I would add as well that similar to Ebola virus, people in intimate contact with Nipah patients can acquire the infection, human to human.
“I’m sure you see the parallels there with Ebola, except unlike Ebola, which has its traditional homeland in sub-Saharan Africa, Nipah is here in Asia.”
Nipah was at first misdiagnosed in Malaysia as Japanese encephalitis, because of the swelling of the brain that occurs.
“When it is transmitted to man, it can cause an extremely serious encephalitis, sometimes with pneumonia, and when people get sick with this, the case fatality rate is about 50%, with substantial serious neurological impairment of a fraction also who survive,” said Clemens.
In Bangladesh, the outbreaks occur because of the traditional drinking of palm wine, a delicacy made from date palm sap. Fruit bats like to hang upside down in the palm trees, with the result that their excretions – urine and saliva can find their way into the sap.
There should be ways to avoid this route of transmission – if not through persuading people to avoid palm wine, then by putting skirts on the trees to keep the bats away, said Clemens.
But that would not end the hidden risk. Changes in people’s behaviour or alterations we make to our environment can precipitate a small outbreak – perhaps with a different and unexpected route of transmission – that becomes something far more dangerous. It happened with Ebola, which spread from rural villages into the cities, where large numbers of people lived close together and were easily infected. That is also the danger with other zoonotic diseases, including Nipah, said Clemens.