As the death toll from the Ebola virus in four West African nations topped 1,000, an official from the World Health Organization said she hopes accelerated efforts to develop treatments might yield more medicine by the end of this year.

Marie-Paule Kieny, assistant WHO director general, said she hopes that work to produce more of the medication developed by a small San Diego biopharmaceutical company, as well as other drugs, could result in wider availability sometime late in 2014 -- perhaps between November and January of 2015.

WHO said Tuesday that the death toll in Guinea, Sierra Leone, Liberia and Nigeria had reached 1,013. A small number of doses of an experimental treatment -- perhaps 1o total, Kieny said -- were exhausted with their distribution to Liberia on Monday for the treatment of two doctors there who have been stricken by the virus, according to Mapp Biopharmaceutical, which developed the drug.

The shortage of medications amounts to "a market failure," Kieny said. "It’s a market failure because this is typically a disease of poor people in poor countries, and so there is no market." As a result, she said, "there are no clinical stockpiles," and the best authorities can do is "accelerate development and scale up" as quickly as possible.

As the worst Ebola outbreak in history continues unabated, Kieny and WHO announced that a panel of experts convened by the organization had determined on Monday that the use of controversial experimental treatments for the disease is ethical. There is no cure for Ebola, but several of the treatments are in various stages of clinical development.

Two American patients who were sickened while treating the outbreak in Liberia have received  ZMapp. Both are improving after being flown to the United States for treatment in an Atlanta hospital. But a Spanish priest who was being treated with ZMapp died on Tuesday, according to Agence France-Presse.

Kieny also became the first official to say publicly that ZMapp appeared to help the two U.S. missionaries, Kent Brantly and Nancy Writebol, who were the first to receive it. The drug had never been tested on humans before it was given to them in recent weeks.

But she said her impressions were based on media reports. Authorities have said it's impossible to know whether a medication works, or has harmful side-effects, based on two patients.

"I haven’t seen their medical records," she said. But in light of the "dramatic and rapid" improvement both experienced, it is "highly probable this has been due to the administration of the drug," she said.

Liberia said Tuesday that it would give ZMapp to two doctors, Zukunis Ireland and Abraham Borbor, who had fallen ill with the virus while treating other patients. The company that manufactures ZMapp said Monday that it has exhausted its supply of the treatment after sending the last doses to Liberia.

"Ethical criteria must guide the provision of such interventions," WHO said in a statement Tuesday. "These include transparency about all aspects of care, informed consent, freedom of choice, confidentiality, respect for the person, preservation of dignity and involvement of the community."

The results of the treatments should then be shared with the broader scientific community to help better understand how these drugs work in a clinical setting.

Kieny said WHO would convene another panel at the end of August to discuss prioritizing distribution of scarce medications.

Meanwhile, beyond Guinea, Liberia and Sierra Leone, several other African nations are closely monitoring ill patients who are suspected to have contracted the disease.

As the worst Ebola outbreak in history unfolds in West Africa, The Post's Joel Achenbach explains how the deadly virus wreaks havoc on the human body. (Davin Coburn/The Washington Post)

So far, aside from those three countries where the outbreak initially spread, only Nigeria, Africa’s most populous country, has confirmed cases of Ebola. Nigeria has confirmed 10 cases, and two of the patients have died.

A Liberian American, Patrick Sawyer, collapsed in Nigeria's most populous city, Lagos, and later became the first patient to die of Ebola in that country. A nurse who treated Sawyer also died.

Nigerian President Goodluck Jonathan called Sawyer a “mad man” for bringing the virus into the country knowing that he was sick, according to Reuters news agency. Sawyer’s sister had reportedly died of Ebola.

Rwanda has isolated a German student, who had recently traveled to Liberia and reported Ebola-like symptoms, until test results can rule out Ebola.

Two men in Benin suspected of having the disease were being tested for Ebola on Monday.

And Senegal has quarantined a suspected Ebola patient while awaiting test results.

In Liberia, aid workers fear that they are losing the battle with the virus.

The situation is “catastrophic,” said Lindis Hurum, the Doctors Without Borders emergency coordinator in Liberia, according to the organization.

The organization, which has been on the front lines of the public health emergency, has more than 600 doctors working in the region, and it says that more are desperately needed.

But these health workers face an acute risk. In Liberia, more than 40 health workers have contracted the disease, according to Doctors Without Borders.

Two Americans working in Liberia contracted the virus while treating and aiding Ebola-stricken Liberians.

Brantly, a doctor,  and Writebol, a volunteer, were both given experimental Ebola treatments and flown from Liberia to a special treatment facility at Emory University in Atlanta.

“I am growing stronger every day,” Brantly said in a statement Friday, according to Samaritan’s Purse, the organization he was affiliated with while working in Liberia.

Brantly said that as soon as he suspected that he was becoming sick, he isolated himself until the tests came back confirming his diagnosis. Writebol was assisting in a decontamination room for nurses and doctors moving in and out of rooms where Ebola patients were being treated.

Writebol's son, Jeremy, said on the NBC's "Today" show Tuesday that his mother is improving as well.

"I've heard the term 'very optimistic' cautiously," Writebol said. "They do feel that recovery is going to be complete for her."

Other missionaries working with Writebol through an organization called SIM USA will return to the United States, but North Carolina officials said they would be quarantined for 21 days as a precaution. That is the maximum amount of time that the Ebola virus can incubate before symptoms begin to show.

So far, the virus has claimed the most lives in Guinea, the country where it is believed to have begun.

This worst outbreak could be traced back to a 2-year-old child who researchers believe might have died in the border town of Guéckédou, Guinea, in early December 2013 --  months before the epidemic was identified, according to a recent paper published in the New England Journal of Medicine.

From there, it spread to neighboring Liberia and Sierra Leone.

A health-care worker from Guéckédou may have catalyzed its spread to several Guinean towns. More than a dozen people contracted the virus in the months before the outbreak was identified in March, leading to a hydra-like transmission chain for the disease.

The clusters of infected patients spread across a swath of geography that now crosses three different countries. Health workers in all three countries were ill equipped to deal with an Ebola outbreak, which had never before occurred in West Africa.