what we know about the deadly Nipah virus.

VIRUS SLEUTHS  Forest officials in the south Indian state of Kerala place a bat found in a well into a container for testing to see if it might be carrying the Nipah virus.

KOCHI, India — The rare and deadly Nipah virus has emerged in southern India, killing at least 11 people and causing more than 25 others to be hospitalized. Although global health officials consider that, so far, to be a relatively small outbreak, they’re worried.

Nipah is on the World Health Organization’s priority list of emerging diseases that could cause a global pandemic, alongside Zika and Ebola.

“This is the first time we’ve seen the virus in south India,” says R.L. Sarita, the director of health services in the Indian state of Kerala. “And we want to make sure that it stays contained here.”

Those infected suffer a quick onset of symptoms, including fever, vomiting, disorientation, mental confusion, encephalitis and — in up to 70 percent of cases, depending on the strain — ultimately death. Here’s what we know, and don’t know, about this incurable disease:

How is the Nipah virus spread?

Several species of fruit bat that live throughout Asia carry Nipah. During outbreaks in Bangladesh from 2001 to 2007, most people contracted the virus by drinking raw date palm sap that virus-carrying fruit bats had also sipped and contaminated (SN: 12/19/09, p. 15).

Bats can also transmit Nipah to pigs and other livestock, which can then pass the infection onto humans. And humans can spread the virus through saliva and possibly other bodily fluids. One victim in the latest outbreak was a 31-year-old nurse who had been treating Nipah patients.

To find the source of this outbreak, health officials in India are testing local bats, livestock and food samples, including mangos that may have been bitten by bats, found in the home of a family that lost four members to Nipah.

HANGING OUT Several species of fruit bats are known to carry the Nipah virus without getting sick themselves. Cases in Bangladesh likely involved greater Indian fruit bats (Pteropus giganteus), such as these pictured. The animals can spread the virus through their saliva and urine.

How does the virus cause infection?

Nipah and its viral cousin Hendra latch onto a proteins called ephrin-B2 and ephrin-B3 on the surface of nerve cells and the endothelial cells lining blood and lymph vessels, researchers have found. Nipah can also invade lung and kidney cells.

Virologists who have studied Nipah’s behavior in animals think that in humans, it initially targets the respiratory system before spreading to the nervous system and brain. Most patients who die succumb to an inflammation of blood vessels and a swelling of the brain that occurs in the later stages of the disease. 

Why are epidemiologists worried about Nipah?

“The No. 1 reason is that it’s just so lethal,” says Linfa Wang, who heads the emerging infectious diseases program at the Duke-NUS Medical School in Singapore. In fact, the villain virus in the 2011 film Contagion was based on Nipah .

Since the virus was first documented in 1998, there have been small, contained outbreaks almost every year in southeast Asia and Bangladesh.

But Nipah has the potential to spread farther — due to the fact that its fruit bat carriers live across a wide range extending from Australia to West Africa.

In addition, some strains are more lethal than others. An outbreak in Malaysia in 1999 was caused by a strain with a 30 percent mortality rate, while the Bangladesh outbreaks involved a different strain that killed 70 percent of infected humans. Scientists aren’t sure why the mortality rates are so different.