Tobacco plants grow in a controlled environment at the Kentucky BioProcessing facility in Owensboro, Ky. The company is using tobacco plants grown at this facility to help manufacture an experimental drug to treat patients infected with Ebola. (AP)

It took nearly three decades of tireless research and countless millions of U.S. government dollars to produce a few grams of the experimental Ebola drug that may have saved the lives of two U.S. missionaries stricken by the virus in West Africa.

And now some are asking this question: If the drug did help missionaries Kent Brantly and Nancy Writebol, whose conditions appear to be improving, could the same drug be given to the hundreds of people dying of Ebola in Liberia, Sierra Leone, Guinea and Nigeria?

What would it cost? What are the ethics of distributing a drug that had never been tested on humans in foreign countries — even if medical authorities could persuade people to take it? And how fast could it be done?

“Two months,” said Charles J. Arntzen, a professor at the Biodesign Institute at Arizona State University, who has collaborated for the past 15 years with Mapp Biopharmaceutical, the small San Diego company that produced the experimental serum given to the two Americans. “Maybe they could do it in a month. If they were [already] planning on it, I’m sure they could produce 10,000 doses in a month.”

Anthony S. Fauci, director of the NIH’s National Institute of Allergy and Infectious Diseases, was more cautious in an interview on CNN on Tuesday. “It is not easy to make this serum,” he said. “The number of doses that are available right now, today . . . is less than a handful.

“It really is going to be a supply problem,” Fauci added. “It would take months to produce a significant amount more.”

Only one place has been approved by the U.S. government to produce ZMapp, the cocktail of three antibodies injected into Brantly and Writebol, who contracted the deadly disease in Liberia. That is Kentucky BioProcessing in Owensboro, Ky., where the antibodies are produced in specially modified tobacco plants, which are harvested, ground up into a green liquid, purified and turned into tiny doses — perhaps half a gram or a gram — of the ZMapp that was administered to the two missionaries.

A spokeswoman, Maura Payne, said in an e-mail Tuesday that “KBP is working closely with Mapp, various government agencies and other parties to increase production of ZMapp, but this process will take several months.” Mapp has a three-year, $10 million contract with the U.S. Defense Threat Reduction Agency to produce the drug, according to a spokeswoman for the agency.

The Ebola outbreak in West Africa has sickened more than 1,600 and killed 887 in four countries. On Tuesday, Writebol, 59, a missionary from Charlotte, was flown to an isolation unit at Emory University in Atlanta in the same “air ambulance” that took Brantly there over the weekend.

“Nancy is still very, very weak, but shows continued, but slowed, improvement,” according to a statement issued by SIM USA, the missionary group she works for.

The statement quoted her husband, David Writebol, as saying: “A week ago we were thinking about making funeral arrangements for Nancy. Now we have reason to be hopeful.”

Though the Ebola drug became a public issue only Monday, groups of researchers — funded and aided by a variety of U.S. government agencies — have been working on treatments and vaccines for nearly 30 years. The Canadian government also has funded an array of research into Ebola.

“This isn’t something that happened overnight,” said Tom Geisbert, a professor of microbiology and immunology at the University of Texas Medical Branch in Galveston who has spent almost 25 years on the effort. “All of these started at least a decade ago.”

Answers to the riddle of Ebola — discovered in Central Africa in 1976 — have been a long time coming in part because working with the virus in a lab requires myriad safety protocols and layers of safety gear. That slows down the daily research process. “It takes about three times as long to do anything,” Geisbert said.

Perhaps more significantly, drugmakers traditionally have shown little interest in pouring resources into such research, because outbreaks occur only sporadically and historically have affected only a small number of patients.

“There’s been no financial incentive for pharmaceutical companies to develop these countermeasures,” Geisbert said. “It just comes down to dollars.”

That has left the government to fund research into Ebola, but even that effort took many years. For years, there were only a handful of Biosafety Level 4, or BSL-4, labs — the only facilities secure enough to handle the most dangerous pathogens — operating in the United States.

That landscape changed dramatically after the terrorist attacks of Sept. 11, 2001, after which the government swiftly funded construction of a wave of BSL-4 labs and put a premium on bioterrorism research.

“It was really post-9/11 that the funds were put into biodefense,” said Geisbert, who spent most of the 2000s working on a potential Ebola vaccine at the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick, Md. “Over the last five to 10 years, there’s been tremendous progress.”

That progress includes ZMapp, as well as the potential vaccine that government officials have put on a fast track for early-stage human trials this fall. But Geisbert said four or five promising vaccines and three post-infection treatments for Ebola remain in various stages of development. All have received years of research and significant grants from U.S. agencies such as the NIH or the Department of Defense. “It’s just a matter of time; there’s obviously a lot of interest now,” he said.

The cost of any effort to help West African Ebola victims is a matter of speculation; only Mapp and a few others would know, and they have declined to answer questions this week. But Arntzen said any government, especially the United States, could afford it.

Would the effort violate ethical guidelines? That seems unlikely, said Ezekiel Emanuel, chairman of the Department of Medical Ethics and Health Policy at the University of Pennsylvania.

“When it’s life or death and you don’t have any options . . . something that has a potential to increase your chances seems like a good thing,” he said. “It’s hard to hurt you worse than the disease is going to hurt you here. That’s not to say it can’t happen.”

Within the United States, the Food and Drug Administration must grant a “compassionate use” waiver before any patient in a dire situation can legally receive an experimental drug. The FDA tends to grant the overwhelming majority of requests it receives, but it cannot force a drug company to provide an unproven drug to a patient.

Mark Berman and Alice Crites contributed to this report.