U.S. and Canadian researchers have successfully treated monkeys infected with the deadly Marburg virus by using a vaccine they developed several years ago. But, there may be obstacles in they way of getting this therapy to market.
The Marburg vaccine is the result of a collaboration by U.S. Army infectious disease researchers and their counterparts at the Canadian Public Healthy Agency. It is part of an effort to develop protections against possible biological warfare agents.
The highly virulent Marburg virus, like the closely related Ebola virus, can cause massive internal bleeding, organ failure, fever, shock and delirium, and usually death. An outbreak in Angola last year killed more than 300 people, 90 percent of those infected.
The U.S. and Canadian scientists had created the Marburg vaccine by removing a gene from a harmless virus and replacing it with a gene for a Marburg virus surface protein. Last year they reported that inoculations prevented the disease in animals that were infected weeks later. Now, they show in the journal Lancet that shots protected monkeys that were already infected.
"This is kind of like [how] rabies vaccine is used. The vaccine is actually given after the challenge," said U.S. Army virus researcher Thomas Geisbert, who is part of the team that infected eight monkeys with high doses of Marburg virus.
The scientists injected five of the animals with the vaccine 20 to 30 minutes later, but left the other three untreated. Geisbert says these three died by day 12, but the five vaccinated monkeys remained healthy.
"Two or three of the animals had very mild low grade fevers around day six, but the animals never stopped eating," he said. "There was no evidence of clinical illness whatsoever in these animals."
The results suggest that the vaccine could be an effective treatment for the disease after exposure for patients or health workers and relatives exposed to a patient. Geisbert says his team is beginning to conduct studies on how long after infection the vaccine would still offer protection. He says the monkey study indicates a period of one to two days, but the window of opportunity could be longer.
"We're talking about a worst-case scenario in monkeys where we intentionally inject these animals with an incredible amount of virus," he noted. "But in the real world, where you have natural outbreaks in Africa, people are probably not getting exposed to these kinds of doses. So in that case you probably would have a lot more time."
In a commentary published in the Lancet, Stephan Becker of the Robert Koch Institute in Berlin, Germany calls the research good news because there are no drugs to treat Marburg virus. But he says the likelihood of developing commercial vaccines against Marburg and Ebola is dim. Fortunately there are too few infected people to allow researchers to test the effectiveness of drugs and create a market for drug companies.
Becker suggests that the current effort to develop biological warfare treatments might bring about just enough vaccine development to allow treatment in emergency situations, such as a laboratory accident with the viruses or protection of health workers in a Marburg or Ebola outbreak.
