Scientists hunting treatments for Ebola and related diseases are trying several approaches. So far, the following have only been tested against the virus in animals:
Small Molecules: These are drugs that can be put into a pill. BCX4430 is from a class of drugs called nucleoside analogues. These molecules may look a lot like the building blocks of the virus' own genetic material (RNA instead of DNA), but the drugs end up preventing the virus from reproducing.
Estrogen Blockers: A few of these FDA-approved medicines, including the fertility drug Clomid, turn out to protect rodents against Ebola in the laboratory, but nobody knows why. It's apparently not related to the drugs' effects on estrogen in the human body.
Small Interfering RNA (siRNA): These snippets of RNA are custom-tailored to bind to a virus' RNA while it is reproducing, and this kills the virus.
Therapeutic Vaccines: Scientists have produced vaccines against Ebola by engineering a different virus, such as vesicular stomatitis virus, to include harmless bits of the Ebola virus. Vaccines are generally designed to protect against infection, but this vaccine may also be useful after a person has been exposed to Ebola to prevent illness.
Engineered Antibodies: Immune system proteins called antibodies attach to foreign substances such as viruses and help a person fight off an infection. Scientists have tailored a particular sort, called monoclonal antibodies, to attack Ebola viruses and related species. Monkeys given the antibodies soon after exposure to what would normally be a lethal dose of Ebola survived.
The Ebola outbreak in West Africa is terrifying because there's no drug to treat this often fatal disease. But the disease is so rare, there's no incentive for big pharmaceutical companies to develop a treatment.
Even so, some small companies, given government incentives, are stepping into that breach. The result: More than half a dozen ideas are being pursued actively.
And these are boon days for drugs that can treat viruses. Think of treatments for AIDS and hepatitis C.
Potential treatments for Ebola pursue many strategies. These include conventional drugs, custom-built antibodies, and vaccines that are designed not simply to prevent the spread of a disease, but to treat it in people who are in the early stages of infection.
Each idea has shown some promise in animals. But nothing has yet passed critical human testing, so there's nothing ready to be tried during the current outbreak.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, is hopeful about this multipronged approach, but says, "I think it's really too early to make a prediction about what is the more or less promising one among them."
One challenge is that there are several different species and strains of Ebola-like viruses, so there may not be a one-size-fits-all solution.
But one experimental drug could conceivably fit that bill. It's called BCX4430. Travis Warren at the U.S. Army Medical Research Institute for Infectious Diseases lab in Frederick, Md., has been working on this antiviral drug.
"It worked great against both Ebola virus and [the closely related] Marburg virus" when tested in mice, he says. It also protected guinea pigs from these viruses and yellow fever.
So the next set of tests was in a small number of monkeys who had been infected with Marburg virus.
"When we started the drug either 24 hours or 48 hours after the infection, 100 percent of those animals survived," Warren says.
It's notable that this drug is being developed by a small company, called BioCryst Pharmaceuticals.
"It just wouldn't make the cut at a major company," says Dr. William Sheridan, BioCryst's medical director, who once worked at the drug giant Amgen.
Ebola, scary as it is, has only made about 2,500 people sick since it was discovered in 1976, killing about 1,700 of them. So the market for a drug like this is tiny.
Still, Sheridan says his company has good reason to pursue it, beyond his desire to address an important public health issue.
"There is a market, and the market is the U.S. government," he says.
The government has promised to buy a stockpile of drugs that are effective against Ebola, in case someone should try to use it as a biological agent on the battlefield, or in an act of terrorism. Federal agencies also are helping to pay for the research, so the company is pushing forward as quickly as it can.
"We're currently [manufacturing the] drug and will be conducting typical animal safety experiments that you typically do before you put drugs in humans," Sheridan says. "And once that's successfully completed, I anticipate by the middle of next year that we should have completed phase one studies in people."
Phase one tests will tell them whether the drug is relatively safe, but it won't tell them whether it would actually be an effective treatment. Assuming the drug seems safe, it would be ready for testing in a future outbreak of Ebola.
Of course, most potential drugs don't live up to their early promise, and there's no assurance this one will, either.
But Travis Warren at the Army lab says that given all the advances in developing drugs to treat viruses, something will emerge out of this broad quest for an Ebola drug.
"I'm absolutely certain it will happen," Warren says. "It's just a matter of time."