A new treatment has successfully protected monkeys infected with Marburg virus, a disease with a course so similar to Ebola's that it's impossible to clinically differentiate the two, scientists announced Wednesday.

Though the technique has not yet been tested in people, the development has researchers noting that what's helpful for Marburg could well be helpful for Ebola, which is now seeing its worst-ever outbreak, claiming more than 1,350 lives in West Africa.

"This technology may have potential for combatting Ebola," says Thomas Geisbert of the University of Texas Medical Branch in Galveston, senior author of the study, published in the journal Science Translational Medicine.

The study marks the first time that a group of primates could be protected from the Marburg disease at a late stage of infection, including after symptoms were already present.

Science is still in the animal-research stages for both Ebola and Marburg viruses. Like the experimental treatment used to care for three health workers sickened with Ebola, this treatment for Marburg virus has yet to be tried in humans. But results from the monkey study are promising.

In the new study, 16 macaques were infected with highly lethal doses of Marburg virus. The monkeys were treated with the experimental therapy, siRNA, at different times, ranging from 45 minutes to three days after infection. All 16 of the treated monkeys survived. A control group of macaques were similarly infected with Marburg, and all of them died by the eighth day.

With funding, a clinical trial of the anti-Marburg approach could be done in about a year, says Geisbert.

Viral Siblings

Ebola and Marburg viruses are close and deadly kin. The viruses are the only two known members of the filovirus family, which can cause severe hemorrhagic fever and often death.

Both viruses spread to humans from animals, then spread among humans through contact with bodily fluids. Both are marked by severe bleeding from orifices, and neither has an approved vaccine or drug for treatment.

"This is a major step toward treatment of Marburg, which can be as lethal as Ebola," says Gaya Amarasinghe, a biochemist at Washington University in St. Louis. "These findings are from a monkey model, and that's a very relevant model for filoviral infections."

In fact, researchers including Geisbert found they could protect monkeys from Ebola virus using the same technology as in the new Marburg study, a result published in 2010 in the journal Lancet.

"It was the same species of Ebola in the current outbreak," says Geisbert. "The difference is that that study examined treatment shortly after exposure. It did not look at initiating treatment at signs of illness."

Combining Tactics

An experimental treatment for Ebola called ZMapp leapt ahead of normal research and approval processes when two American health workers and a Spanish priest were treated experimentally, before any human trials were conducted.

The Americans are so far doing well, while the Spanish man has died.

The two experimental treatments follow different biological routes. ZMapp is composed of three monoclonal antibodies from the tobacco plant that bind to the protein of the Ebola virus. "Basically, [ZMapp] interferes with the way that Ebola virus attaches to and enters the host cells," says Geisbert.

The other technology is an siRNA, or "small interfering RNA," consisting of small pieces of RNA that can inhibit protein production. This interferes with how the virus grows once it gets into cells.

Because the two treatments work differently, combining them might work better than either one alone, an approach that Geisbert's team is developing. Mixing and mingling promising treatments harkens back to scientists working on AIDS treatments in the 1990s who discovered that combination retroviral therapy produced better results than any one drug.

"Combining successful therapies will likely extend the treatment window, if these different approaches can work well together," says Amarasinghe.

Behind the Clock

While the World Health Organization has concluded that it is ethical to use unproven drugs to try to combat the outbreak of Ebola, experimental drugs simply are not available in sufficient quantity. In an opinion piece published Wednesday in the journal Nature, University of Oxford epidemiologist Oliver Brady writes that "even under a conservative scenario, up to 30,000 people would have so far required treatment or prophylaxis in the current outbreak."

The world's medicine cabinet has thus far been able to provide experimental drugs to only three people.

The real challenge right now, says Alta Charo, professor of law and bioethics at the University of Wisconsin, Madison, is stopping the current outbreak using available methods. That means providing gloves and protective suits for health care workers in West Africa, increasing the number of health care workers, isolating the sick, educating affected communities, supplying antibiotics, and promoting alternatives to dangerous cultural practices like close handling of the newly dead.

Whether for a future outbreak of Marburg, or today's outbreak of Ebola, "the most important way to reduce the death toll is through public health measures," Charo says.

Update: The number of Ebola deaths has been updated to reflect the most recent numbers from the World Health Organization as of August 20.