Experimental Treatments That Could Help Stop Ebola

— -- intro: Federal officials have confirmed that medical teams have given two Ebola-infected nurses from Dallas experimental treatments to help them fight the deadly virus that has already killed at least 4,555 people, mainly in West Africa, according to the World Health Organization.

While testifying before a congressional panel on Thursday, Dr. Luciana Borio, assistant commissioner for counter-terrorism policy for the U.S. Food and Drug Administration, said “every Ebola patient in the U.S. has been treated with at least one investigational product.”

Two nurses from Texas Health Presbyterian Hospital in Dallas were diagnosed with Ebola after treating Thomas Eric Duncan, a Liberian man who contracted the disease before arriving in the U.S.

Duncan died on Oct. 8 making him the first person to die from Ebola in the U.S. The ongoing worst-ever Ebola outbreak has pushed doctors and health care officials to search for new or experimental treatments.

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Several companies have products in development aimed at combating the virus that can lead to a deadly hemorrhagic fever. Before the outbreak, doctors generally used supportive care, including intravenous fluids and oxygen to help patients.

While every U.S. patient and many patients from European countries have received some kind of experimental treatment, the effectiveness of these treatments remains unclear without more rigorous scientific study.

To better understand how doctors can approach treating the deadly disease, here is a list of some experimental treatments in the works.

Do you have questions about Ebola in America and elsewhere in the world? Post them to the Good Morning America Facebook page tagged #EbolaFactsABC. At 1 p.m. ET, ABC News will hold a live Ebola Q&A session with George Stephanopoulos and ABC News chief health and medical editor Dr. Richard Besser.

quicklist: 1category: The Experimental Treatments Designed to Fight Ebola title: Brincidofovirurl:text: An antiviral drug called brincidofovir was used to treat Thomas Eric Duncan, the first person to be diagnosed with Ebola in the U.S., and Ashoka Mukpo, an American freelance cameraman who contracted the virus while on assignment in Liberia.

Brincidofovir is a modified version of an existing drug called cidofovir and works by inhibiting the replication of a virus, according to Chimerix, a pharmaceutical company based in North Carolina.

The medication is experimental and before the outbreak had not been tested to combat Ebola in humans or primates, according to Chimerix.

Duncan died on Oct. 8 after being hospitalized at Texas Health Presbyterian Hospital for over a week. Mukpo was transported from Liberia to the biocontainment unit at Nebraska Medical center, where he remains in isolation. media:25931828

quicklist: 2category: The Experimental Treatments Designed to Fight Ebola title: ZMappurl:text: The most well-known of the experimental treatments was used on the first two American health workers to be diagnosed with Ebola in Liberia.

Dr. Kent Brantly and Nancy Writebol were the first humans to be given the drug, which had previously been tested only in primates, according to health officials. The drug is a mix of three synthetic antibodies that can attack the structure of the Ebola virus.

This cocktail of antibodies specifically attack the virus' spike-like protrusions used to invade cells and replicate. It remains unclear whether the drug helped the patients get over their infection due to the small number of people given the drug.

Of the seven people known to have been given ZMapp, five survived the virus.

In August, Mapp Pharmaceuticals announced the supply of ZMapp had been exhausted and that it would take weeks to months to manufacture more of the medication. media: 25073030

quicklist: 3category: The Experimental Treatments Designed to Fight Ebola title: ZMaburl:text: One component of ZMapp has been used to help infected patients in Spain and Norway fight the virus. Called ZMab, the drug consists of a cocktail of three mouse antibodies developed to fight the virus.

In theory the antibodies will give a patient's immune system a head start against the virus and a chance to create their own antibodies and fight off the virus.

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quicklist: 4category: The Experimental Treatments Designed to Fight Ebola title: Convalescent Serum url:text: Doctors have also tried an older method of treatment called “convalescent serum,” which involves giving an infected patient plasma from another patient who has recovered. In theory, that surviving patient will have developed antibodies that can help the infected patient fight off the virus.

In the U.S., Dr. Kent Brantly has donated plasma to at least three patients, Dr. Rick Sacra, Nina Pham and Ashoka Mukpo. The serum can also be a limited option since a donor and recipient must have a matching or compatible blood type.

Since Brantly is blood type A+, his plasma could not be used to help Thomas Eric Duncan, whose blood type was B+, according to his family.

While there was no hard evidence that the plasma donation could help a patient with Ebola, Dr. Phillip Smith, who treated Dr. Rick Sacra as the head of the biocontainment unit at Nebraska Medical Center, said it was a fairly safe procedure and there was a chance it provided Sacra critical time to allow his immune system to fight off the Ebola virus.

"We're hoping it [would] jump-start his immunity. To survive [Ebola] you have to build up enough antibodies to [fight the virus]," Smith told reporters. "We were hoping to buy him some time, to give his immune system time to battle the disease."

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quicklist: 5category: The Experimental Treatments Designed to Fight Ebola title: TKM-Ebola url:text: The pharmaceutical company Tekmira, based in Canada, was the second experimental Ebola therapy to be used in the U.S. after the ZMapp supply was exhausted.

Dr. Rick Sacra was given a dose of the Tekmira drug, TKM-Ebola, when he arrived in Nebraska for treatment earlier this month, doctors said.

Thomas Geisbert, a virologist studying Ebola at the University of Texas Medical Branch in Galveston, Texas, worked on the production of TKM-Ebola and said that the medication works by targeting a specific region of the virus' genetic material and preventing it from making more copies of itself.

"It interferes with the virus genetic blueprint," Geisbert explained.

The experimental drug, which was partially funded by the Department of Defense's Threat Reduction Agency, was tested extensively in primates and it was approved for phase one of human trials this January by the U.S. Food and Drug Administration.

quicklist: 6category: The Experimental Treatments Designed to Fight Ebola title: Sarepta's Ebola Anti-Viral Medicationurl:text: One other option for doctors will be a drug designed by the Massachusetts-based Sarepta Therapeutics.

Chris Garabedian, president and CEO of Sarepta, said the drug works by targeting the protein responsible for replicating the Ebola virus in the host. In primate studies, the survival rate for subjects treated with the medication was between 60 to 80 percent, according to Garabedian. The drug was developed originally due to a contract with the Department of Defense.

However, there are just 25 doses currently ready for immediate use, according to a spokesperson for Sarepta. There is material for another 100 doses, but that material is not yet ready and would take months before it would be ready for use in patients.

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quicklist: 7category: The Experimental Treatments Designed to Fight Ebola title: Biocryst Pharmaceuticals' BCX4430 url:text: One other drug is being developed by a North Carolina-based pharmaceutical company collaborating with the National Institutes of Health.

The antiviral drug BCX4430 could be used to treat different kinds of hemorrhagic fever including Ebola, according to Biocryst Pharmaceuticals.

The Ebola drug attempts to stop the virus by targeting a key enzyme in the virus, according to the company's website.

The drug will start the first phase of human trials later this year, according to the U.S. Centers for Disease Control and Prevention.