An experimental drug has protected monkeys against infection with Nipah virus, a lethal disease and emerging pandemic threat for which there is no approved vaccine or cure, scientists reported recently.

The antiviral drug, remdesivir, also is being tested against the Ebola virus in the outbreak now underway in the Democratic Republic of Congo.

The only current treatment for Nipah virus infection is a monoclonal antibody that is still experimental; it was tested during an outbreak in India last year.

In the new trial, eight African green monkeys were given lethal doses of Nipah virus. Half of them later got intravenous remdesivir. All four monkeys that got the drug survived; the four that did not died within eight days.

If the drug wins approval for use against Nipah, “it will give us an extra treatment that could be used relatively quickly,” said Emmie de Wit, a virologist at the National Institute of Allergy and Infectious Diseases and one of the study’s lead authors. “The average person who reaches a hospital dies within two days, so it’s hard to protect them once they’re infected.”

Ebola and Nipah belong to different viral families, but remdesivir — made by Gilead Sciences and also known as GS-5734 — appears effective against both.

In mice or cells cultivated in the laboratory, the drug also has shown some effectiveness against two other pandemic threats: Lassa fever and MERS coronavirus. It also is effective against respiratory syncytial virus, which infects children all over the world.

Although the outer shells of all these viruses are very different, their polymerases — the genome-copying enzyme that remdesivir targets — are similar, de Wit explained.

The new study, done jointly by the NIAID and the Centers for Disease Control and Prevention, was published in Science Translational Medicine.

Nipah virus, which causes encephalitis and pneumonia, is lethal in about 70% of cases. It can be caught from animals or transmitted between people.