Researchers are claiming a breakthrough in the battle against the deadly Ebola and Marburg viruses. Outbreaks of both are currently killing people in Africa.
Vaccines against the viruses have proven "100 per cent effective" at protecting monkeys, say the scientists.
The research, published in the latest issue of Nature Medicine, provides hope that vaccines to protect humans from the viruses could be available in the next few years.
Ebola and Marburg viruses both cause haemorrhagic fever, a devastating disease that causes major internal and external bleeding and kills 50-90 per cent of those infected within a few days. There is no cure.
Angola has been in the grips of a Marburg outbreak since 2004. As of 26 May, it had killed 335 of the 399 people who were confirmed to be infected, according to the World Health Organization.
Meanwhile, in the Republic of Congo, Ebola has killed at least 10 people in the past few weeks.
Outbreaks of Ebola in humans have been linked to exposure to infected bushmeat — principally gorillas and chimpanzees (see Ebola passes from animals to humans).
Like humans, the infected primates succumb to haemorrhagic fever and soon die.
The new vaccines are the first to protect non-human primates from both Ebola and Marburg, says Thomas Geisbert, of the US Army Medical Research Institute of Infectious Diseases, one of the lead researchers.
Safety first: Vaccine
researcher working with
samples from the monkeys
Geisbert and colleagues based the vaccines on a virus called vesicular stomatitis virus.
They made it harmless by removing the gene that makes it infectious. They then created the two vaccines by replacing a protein on the surface of the virus with one from the Ebola and Marburg viruses.
They gave the vaccines to macaque monkeys and then exposed them to Ebola and Marburg. The monkeys resisted infection.
The Ebola and Marburg proteins on the vaccines 'primed' the monkeys' immune systems, allowing them to recognise and destroy the Ebola and Marburg viruses and stop them replicating.
"This is a major step forward in combating these pathogens," says Geisbert. "This study lays the groundwork for future trials in humans."
Geisbert says he expects the vaccine to work in people because non-human primates are even more sensitive to the two viruses than humans are.
"The fact that we completely protected non-human primates from disease and death when infected with an extremely high dose of these viruses shows the potential success of these vaccines in humans."
However, he adds that it will take several years to determine the lowest protective doses and only then can human trials begin.
Also, a vaccine for people would need to incorporate a protein from the form of Ebola found in Sudan.
Geisbert told SciDev.Net it could take 18 months or more to get that work done.
"I'm really excited by this new study," says Fons Van Gompel, associate professor of tropical medicine at the Institute of Tropical Medicine in Belgium.
However, he adds that just because the vaccine works in non-human primates, does not necessarily mean it will protect people too.
And conducting clinical trials of a human vaccine in Africa could be difficult, say Van Gompel, noting that during recent outbreaks of Ebola and Marburg viruses, international health workers were threatened by local people.