By Maggie Fox, Health and Science Editor

WASHINGTON, Dec 20 (Reuters) - Carefully designed drugs may be able to treat a variety of new and dangerous viruses, including the Nipah, Hendra and Ebola viruses, researchers reported on Thursday.

They used an approach that has worked with newly designed AIDS drugs known as entry inhibitors, and found it effective against Nipah and Hendra viruses.

These drugs stop certain types of viruses from getting into cells and could provide the first treatment for the mysterious and deadly infections, which have only recently emerged, said Dr. Anne Moscona of Weill Cornell Medical College in New York.

Writing in the Journal of Virology, Moscona and colleagues said they found a piece of a related virus called a parainfluenza virus that will fit in between the attacking virus and the cells it infects.

"These peptides act like door jambs -- their particular shapes prevent 'doors' in the viral 'fusion protein' from closing as they should," Cornell's Dr. Matteo Porotto said in a statement.

"The parainfluenza peptide's shape simply makes it a better door jamb," Porotto added.

"This is really proof of concept," Moscona cautioned in a telephone interview.

No drug is immediately available from the research, she said. "By understanding the mechanism of how they work and how to make them work better, we can design better ones that might be viable."

Nipah virus was first seen when it killed more than 100 people out of 257 infected in Malaysia in 1999. The Hendra virus was first seen in Australia in 1994, when it killed two people and many horses. They are genetically related and both are believed to be carried by bats.

Bats are also suspected of carrying Ebola virus, which has killed several hundred people in outbreaks across Africa -- most recently 35 in Uganda this month.

Moscona's team has been working with another sort of virus called parainfluenza virus, which causes respiratory infections in children. They found a protein particle called a peptide taken from parainfluenza virus can stop Hendra and Nipah viruses from entering and infecting human cells.

"We've been urgently working on this because right now there's absolutely nothing that can be done to stop this fatal, transmissible illness," Moscona said.

The approach should work against a range of viruses that infect human cells by using a protein on the outside that changes shape to break in, Moscona said.

Currently, the peptides that the team has been working with do not last long in the body. A good drug would provide protection for a long time, and might be used both after patients became infected and, in the case of an outbreak, to protect people not yet infected, Moscona said.

"So, we are also developing methods of sustained-release -- for example, encasing the peptide in a polymer pellet that would be injected under the skin. The pellet would then release the drug slowly over the course of a week. That could form a viable method suitable for stockpiling," she said. (Editing by Eric Walsh)

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