Ebola is continuing to kill people across West Africa, but there is still no cure.
Available treatments only ease the symptoms of the disease. People with Ebola are given supportive care, such as intravenous fluids to combat the dehydration caused by bleeding, vomiting and diarrhoea.
Several potential drugs and vaccines are working their way through animal studies and clinical trials, but progress has been slow. On-the-ground trials are almost impossible to conduct, largely because outbreaks in Africa are sporadic and unpredictable. "It is difficult to do conventional clinical trials," says Thomas Geisbert of the University of Texas Medical Branch at Galveston, who is developing vaccines and therapies.
The only treatment to have reached human trials works through a technique called RNA interference. The approach uses RNA molecules – which can block DNA from making proteins – to stop the Ebola virus from replicating.
The drug, called TKM-Ebola, protected monkeys when it was given to them within 30 minutes of being injected with the virus. Safety studies in human volunteers have been paused, however, while the manufacturer gets more information to the US Food and Drug Administration about how the immune system responds to high doses.
Another approach is to inhibit a viral enzyme that is vital to the microbe's survival. A compound that seems to do this, called BCX4430, is currently being tested in animals infected with Ebola.
Even better would be a vaccine against the virus. Perhaps the most promising – also still in animal studies – are those made from a relatively harmless microbe called vesicular stomatitis virus (VSV). The VSV is genetically altered so that a protein on its surface is switched for one of Ebola's proteins. This tricks the body's immune system into thinking it has seen Ebola, and triggers the production of antibodies against the virus. The idea is that, if the immune system encounters the real virus later, it is primed and ready to attack it.
Vaccine as treatment
A vaccine could even be used as a treatment after someone is exposed to Ebola, in the same way that rabies vaccine is used therapeutically. That's because these viruses are incubated for several days before they cause symptoms, so there is time for the vaccine to kick in.
Indeed, in 2009, one of the VSV-based vaccines was given to a German researcher who accidentally pricked her finger with a needle carrying the virus. She survived the incident, but there is no way to know if the virus really entered her body.
Such a strategy would need the vaccine to be given as soon as possible after exposure. "If someone comes in with the full-blown symptoms of haemorrhagic virus, they don't have long, maybe 24 to 48 hours," says Geisbert.
Unfortunately, none of these treatment approaches are close enough to receiving regulatory approval – or even passing the first stage of human safety trials – to be used in Africa now. They may be ready for the next epidemic, though, says Geisbert.