'Nipah has jumped from bats to humans because the natural habitats of bats have been disturbed. There are a lot of viruses out there we don't know about, and disturbing the environment may lead to the transmission of them.'

Now scientists have identified the way the virus infects cells, causing often-fatal encephalitis. This discovery could lead to medications and vaccines to prevent or cure the disease, according to a report in the July 6 online edition of Nature.

Nipah virus is carried by bats. It can be transmitted directly from bats to humans or to pigs and then to humans. The first known outbreak of the virus occurred in Malaysia between 1998 and 1999. That outbreak killed 105 people and sickened 265. The Malaysian government also had to destroy more than 1 million pigs to prevent further spread of the virus. In pigs, the virus causes only about 5 percent mortality.

In Bangladesh, death rates from repeated outbreaks over the past four years have risen to 70 percent. This suggests that the virus may be mutating and becoming more lethal, the researchers said.

Becoming More Lethal

"For the virus to enter the cell it needs to latch on to a protein in the cell," said lead researcher Dr. Benhur Lee, an assistant professor of microbiology, immunology and molecular genetics at the University of California, Los Angeles. Lee's team has found that protein, the cell receptor called Ephrin-B2.

To identify this receptor, Lee's team stitched the Nipah virus to part of a human antibody. They found that the virus attached to the Ephrin-B2 receptor on the cell surface, but did not attach to cells where the receptor had been blocked.

Lee thinks this discovery can lead to drugs that could prevent people from being infected by the Nipah virus. "This is the first step to developing therapeutic drugs that can block the virus from getting into cells," he said. "We have already identified some compounds that might block this interaction."

The virus is becoming more lethal, Lee added. "It seems to be spreading more easily from human to humans," he said.

However, Lee thinks the threat of using the virus for bioterrorism is probably limited to infecting pigs, causing the animals to be destroyed and potentially devastating the hog-farming industry. In the United States, the estimated value of pigs in the hog-farming industry is $8.6 billion, Lee said.

Disturbing the Environment

The reason the virus suddenly appeared in humans is probably due to increased contact between bats and livestock and humans, Lee said. "Nipah has jumped from bats to humans because the natural habitats of bats have been disturbed," he said. "There are a lot of viruses out there we don't know about, and disturbing the environment may lead to the transmission of them."

Lee added, "Now that these viruses have been released into the human population, all we can do is hope to investigate and research them, and hope to come up with therapeutics and vaccines."

Curt Horvath, an associate professor of molecular biology at Northwestern University, called Lee's study "very interesting. It leads to further areas of research."

Horvath thinks there is a potential biodefense threat from Nipah.

"The reason that this virus is on the biodefense priority list is because it is fatal and there is some potential for misuse," he said. "As with all these emerging viruses [like SARS] that appear apparently from nowhere and disappear just as fast, there is a potential that they will come out again. The more we can learn about how the virus gets into cells, the better we will be prepared for another outbreak."

More information: The US Centers for Disease Control and Prevention can tell you more about Nipah virus.