NEW YORK, Aug 20 (Reuters) - An experimental drug from Tekmira Pharmaceuticals Corp helped lab monkeys recover from the most deadly strain of Marburg virus, a close cousin of Ebola, even after symptoms appeared, scientists reported on Wednesday.
The findings, published in the journal Science Translational Medicine, offer a glimmer of hope for treating not only Marburg disease but also Ebola hemorrhagic fever at a relatively late stage of infection.
Tekmira is also developing an experimental Ebola drug that works by a mechanism identical to the Marburg one. The company was ordered to halt the human trial of that treatment earlier this year when some of the healthy volunteers experienced adverse events such as fever.
This month, however, regulatory authorities allowed a modified version of the trial to resume, and the company is considering making the compound available in West Africa's current Ebola outbreak.
Outside experts, while praising the Marburg study as an important advance, also expressed caution given its small size and the problematic safety history of this class of drugs.
All 16 infected monkeys that received the drug, including seven that had symptoms of illness, recovered. Two of the seven received the drug three days after infection, long after scientists feared the virus would have proliferated so extensively and caused such severe organ damage that treatment would be ineffective, study leader Thomas Geisbert, professor of microbiology and immunology at the University of Texas Medical Branch, told reporters.
All five of the infected monkeys that did not receive drug became sicker and sicker, and were euthanized.
Both Marburg and Ebola cause hemorrhagic fever and kill the vast majority of those they infect, with the most severe strains having a 90 percent fatality rate. There are no approved treatments or vaccines.
Other experimental vaccines or drugs have proved effective when given to lab monkeys soon after infection, but it was not clear if, once Ebola or Marburg symptoms appeared, anything would help.
The bigger the window of treatment, the more people could be cured. Many patients do not receive medical care until they have symptoms, which occurs days after being infected.
The findings come as Africa struggles to contain the worst Ebola outbreak in history. With the number of deaths surpassing 1,200, U.S. government agencies have hurriedly issued grants to small biotech companies developing Ebola vaccines or treatments, including NewLink Genetics and Profectus BioSciences.
Gary Kobinger of the Public Health Agency of Canada, an Ebola and Marburg scientist not involved in the new study, called the new study "a clear step forward." But "one has to be careful (basing conclusions on) two animals," he said, referring to the number effectively treated three days after infection.
The Tekmira drug consists of so-called small interfering RNA (siRNA), the sister molecule of DNA. The siRNA binds to the viruses' genetic material and prevents them from proliferating in cells they have infected.
The only similar success in a hemorrhagic virus came last year. When Kobinger and colleagues paired a cocktail of anti-Ebola antibodies made by Mapp Biopharmaceutical with the immune-system compound interferon, the combination cured seven of eight monkeys that received it three days after infection and after symptoms had appeared, they reported last October. (Editing by Michele Gershberg and Matthew Lewis)