Nipah: A Fearsome Virus

In 1998, with no warning or explanation, a fearsome disease took over in Malaysia. Pigs died in large numbers, and the men slaughtering the infected animals also fell ill. They brought it to their families at home, and over half of those who got sick died. It was a virus called Nipah, identified in Kampung Sungai Nipah, Malaysia.

However, there are similarities to Ebola in the way the disease suddenly emerged from animals and then spread among humans. Both cause a threat to life that caught the medical world off-guard.

The story of the Nipah outbreak was told in the 2011 film Contagion. Contagion has stars such as Gwynneth Paltrow, Kate Winslet, and Matt Damon. In the movie, the disease became a global pandemic, killing 26 million people.

In reality, where it spread in Malaysia and Singapore, the death toll from Nipah was 105 out of 265 cases. It also caused the $1bn pig industry to collapse. The disease appeared to come out of nowhere, but as with other viruses, the spread was due to a mixture of human behavior and environmental changes.

The virus is native in fruit bats who can also carry the Ebola virus. The bats were leaving rainforests where logging was causing heavy haze, closing out sunlight and preventing the fruit they ate from growing. However, the drought caused by El Niño made things worse.

Scores of bats were in the orchards near the pig farms of northwest Malaysia. The virus from their saliva was in the fruit they dropped, which the pigs devoured.

Mass culling of pigs finally stopped the Malaysian outbreak in May 1999.

Professor John Clemens, executive director of the International Centre for Diarrhoeal Disease Research, says it is very similar to Ebola. However, unlike Ebola, whose homeland is in Africa, Nipah is in Asia.

In Malaysia, Nipah was first thought to be Japanese encephalitis, due to the swelling of the brain.

Clemens says when it is in humans, it can cause a serious encephalitis, sometimes with pneumonia. When people get ill with this, the case fatality rate is 50%. Out of those who survive, a fraction end up with serious neurological impairment.

The outbreaks occur in Bangladesh because of the traditional drinking of palm wine, a delicacy made from date palm sap. Fruit bats enjoy hanging upside down in the palm trees, resulting in their excretions, like urine and saliva, finding their way into the sap.

There are ways to avoid this route of transmission, whether it is convincing people not to drink palm wine or putting skirts on the trees to keep the bats away.

However, that would not end the unknown risk. Changes in behavior or environmental alterations can accelerate a small outbreak, maybe with a different route of transmission, and could become something far more dangerous. Ebola spread from rural villages into the cities, where scores of people living close together were easily at risk of infection. That is also the same danger with other zoonotic diseases, including Nipah.