Marburg virus is closely related to the Ebola virus. The two viruses are the only members of the filovirus family. Both viruses cause severe hemorrhagic fever in humans and non-human primates. (C. Bickel/Science Translational Medicine)

Researchers for the first time have effectively treated monkeys infected with the deadly Marburg virus, even when the treatment began days after the animals were exposed and had begun showing symptoms, according to a new study.

The findings, published Wednesday in the journal Science Translational Medicine, could prove significant in part because the type of Marburg involved — the most lethal form — is closely related to the Ebola virus responsible for the devastating outbreak in West Africa.

Thomas Geisbert, a primary author of the study and a professor at the University of Texas Medical Branch in Galveston, said the Ebola outbreak highlights the “clear and present danger” such viruses pose to human health and underscores the need for the development of effective countermeasures.

There are no approved vaccines or drugs to treat the most deadly strain of Marburg — or Ebola, for that matter — and prior to Wednesday’s findings, no post-exposure treatment had been shown to entirely protect non-human primates.

Geisbert said the study, which was funded by the U.S. government and conducted in collaboration with the drug’s manufacturer, Canadian firm Tekmira Pharmaceuticals, involved giving 21 rhesus monkeys lethal doses of the MARV-Angola virus.

Sixteen of the monkeys received doses of Tekmira’s drug, which uses “small interfering RNA,” or siRNA, a technology that interferes with how the virus grows once it gets into a cell. Some of the monkeys were treated as soon as 30 minutes after being infected, while others received treatment beginning three days after exposure. All of them survived, while the monkeys that received no treatment died.

Geisbert said the results suggest the drug has “real-world utility,” given that it worked days after the animals were infected and after the onset of symptoms. He added, “This approach has the potential for use against all filoviruses [such as Marburg and Ebola].”

He added that further studies are needed to determine just how long after exposure to the virus the drug can be given and still be effective, and he said human trials are needed to ensure the drug’s safety.

This is an electron microscope photo of the Marburg virus. (Thomas Geisbert, University of Texas Medical Branch)

The findings come as governments and private companies have reignited efforts to speed up the development of medications and vaccines for virulent diseases amid the Ebola outbreak in West Africa. Last week, the World Health Organization said it would be ethical to offer unapproved treatments to Ebola victims, given the disease’s high mortality rate.

Tekmira previously had begun “Phase I” human trials for an Ebola treatment but put those efforts on hold after the Food and Drug Administration raised questions about safety. However, the FDA has removed its “clinical hold,” potentially clearing the way for the use of the experimental drug in patients.

Another experimental drug called ZMapp recently got international attention after it was used to treat two Ebola-stricken U.S. missionaries in Liberia. The San Diego-based company behind ZMapp said last week that its supply of the drug was exhausted after it sent its last doses to Liberia, but it is working with the government to determine how quickly more could be produced. Unlike the Tekmira drug in Wednesday’s study, ZMapp uses a cocktail of three “monoclonal antibodies” to essentially block the Ebola virus from entering cells.

Amesh Adalja, a member of the public health committee of the Infectious Disease Society of America and an infectious disease doctor at the University of Pittsburgh, called Wednesday’s study fascinating and exciting. He said it offers another example of how research into treatments for highly infectious diseases such as Marburg and Ebola — an effort that was accelerated after the Sept. 11 terrorist attacks — is finally paying off.

“We are starting to see the fruits of that,” he said. “It’s not overly optimistic to think we’ll be able to change the way these viruses are treated five to 10 years from now. These viruses will not be as deadly.”

For now, Adalja said, even an array of promising drugs in development can’t bring the Ebola crisis under control. What’s needed is adherence to traditional public health measures such as quarantining patients and tracking down those who might have the disease.

“It would be a mistake,” he said, “for people in those countries to think that these drugs are going to be available in large enough quantities to alter the course of this outbreak.”

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