Doctors have turned to an age-old form of antiviral therapy in the fight against Ebola.
The treatment, endorsed by the World Health Organization, involves infusing blood plasma from convalescing survivors into a newly diagnosed patient.
Amid a growing Ebola crisis in West Africa and no proven therapy or vaccine, WHO also has issued interim guidance on the collection, storage and use of blood plasma from survivors in the convalescent phase. Their blood, WHO officials say, is rich in infection-fighting antibodies.
"Desperate times call for desperate measures," Dr. Bruce Farber, chief of infectious diseases for the North Shore-Long Island Jewish Health System, said referring to the infusions.
At least one of the two infected Dallas nurses, Nina Pham, 26, received a plasma transfusion from Ebola survivor Dr. Kent Brantly, the medical missionary who was infected while treating Ebola patients in Liberia.
Pham was flown late last week to the National Institutes of Health's Clinical Center, the premier research hospital in the United States, for further care.
She contracted Ebola while caring for Thomas Eric Duncan, the Liberian national who died nearly two weeks ago.
Another nurse to contract Ebola, Amber Vinson, was being treated at Emory University Hospital in Atlanta.
Doctor: 'In theory it works'
Farber said the plasma treatment is a throwback to the 1920s and '30s when it was more widely -- but not always successfully -- used.
In those days, plasma therapy filled a void in an era devoid of antimicrobials and was administered to patients with either bacterial or viral infections.
"Blood consists of two major components, the red cells and the plasma," Farber said, explaining that when blood is centrifuged -- spun at high speed -- it separates into the two constituents. The plasma portion contains the antibodies.
Antibodies, infection-fighting proteins, develop following exposure to a virus, such as Ebola. Infusing a newly diagnosed patient with it provides the protein components to fend off the disease.
"In theory it works," Farber said, "but it basically requires that you have enough antibodies in the plasma for the process to be effective.
"It's certainly important to emphasize that there are many questions as to its efficacy, especially for it to work on a large scale. In that case, you would need a large pool of survivors for it to be useful."
Farber said plasma treatments never could be considered a cure and they have not worked in numerous infections, particularly HIV.
Plasma infusions, nevertheless, offer an expeditious way to provide therapy for a virus at the center of an explosive outbreak.
West Africa cases skyrocket
Although the Ebola virus has been known since 1976, the infection never threatened populations the way it does now.
In the past, it largely had been a sporadic problem in Central Africa in relatively small outbreaks, according to WHO data. Its recent emergence in West Africa has taken global health experts by surprise.
The exponential growth of the disease is decimating populations in Liberia, Guinea and Sierra Leone -- and there is no end in sight to the skyrocketing number of cases, WHO officials say.
The U.S. Centers for Disease Control and Prevention estimates 8,997 total cases of the disease in the three countries since spring, and 5,006 laboratory-confirmed cases.
The official number of deaths was 4,493 as of Friday, but experts say hundreds -- possibly thousands -- of people may have died without ever being officially counted.
It is the continuing expansion of the highly contagious infection that poses a threat to the rest of the world, experts say.
"Regardless of whether you think Ebola is going to turn into a pandemic or you're worried for your children or you operate from compassion, the only way to guarantee safety for all is to end the epidemic at its source," said global health expert Laurie Garrett, a senior fellow at the Council on Foreign Relations in Manhattan. Garrett, formerly of Newsday, reported on a major Central African outbreak of Ebola in the 1990s.
New studies on immunity
Some scientists see the outbreak as raising new lines of research, especially regarding human immunity.
Last week in the medical journal The Lancet, scientists from the Center for Computational Biology and Bioinformatics at the University of Texas in Austin found that while Ebola kills some people, it may be immunizing others.
Dr. Steve Bellan said a proportion of people in West Africa are exposed to the virus but do not develop infection. "There is evidence that this may happen frequently," Bellan said Friday. "And this may be an important missing piece in how Ebola is interacting with the population."
Bellan said it's unknown whether the exposure amounts to long-term immunity. He doubts that antibodies from someone who was exposed but didn't develop symptoms would be appropriate for a plasma infusion.
Dr. Vincent Racaniello, the Higgins Professor of Microbiology and Immunology at Columbia University in Manhattan, said while there are some unknowns about the virus, there are several features that are well established. It will never become airborne, he said.
"Viruses are transmitted in a certain way and it's very, very difficult for them to change," Racaniello, a virologist, said. "Changing makes viruses very sick.
"So it is fixed," he said of the mode of transmission.