New Ebola infections in virus-ravaged Liberia appear to be declining for the first time in months, the World Health Organization said Wednesday.

Until now, officials have been suspicious of this encouraging trend, thinking it might be an artifact of poor data collection, a symptom of chaos in countries that were overwhelmed by the crisis. But Bruce Aylward, a top WHO official, said Wednesday that the decline in new cases “is real,” measured by scores of empty beds in Ebola clinics, fewer cases confirmed by laboratory tests and a drop in burials by specially trained teams.

Still, the WHO and other officials remain wary because the nature of this outbreak has been one of unpredictable surges and declines.

“It’s like saying your pet tiger is under control,” Aylward said. “This is a very, very dangerous disease.”

Aylward, assistant WHO director-general in charge of the Ebola response, had said in a news conference two weeks ago that without significant progress against the epidemic, there could be 5,000 to 10,000 new cases per week by the beginning of December in the West African countries hardest hit by the disease. That dire outlook was consistent with other forecasts by epidemiologists who have warned that there would be catastrophically high numbers of Ebola cases without a robust response.

In Liberia, reports of new Ebola cases have tapered off.

But Aylward said Wednesday that it appears an increase in the number of safe burials, tracing of people who have had contact with Ebola patients and an aggressive public awareness campaign have been helping. He warned that even a few unsafe burials could make the disease flare up again in places where it seems to have been contained.

“The danger now is that instead of a steady downward trend, we end up with an oscillating trend where the virus goes up and down,” he said.

Liberia is one of the three countries most affected by the epidemic, which is also raging next door in Sierra Leone and Guinea. The cumulative number of cases in those three countries, dating to the beginning of the outbreak, jumped to 13,676, according to a WHO update issued Wednesday. That’s an increase of more than 3,000 cases from the WHO report issued five days earlier.

The organization said the sharp increase reflected a re­examination of older data rather than a surge in new cases. The WHO reported 4,910 deaths from Ebola in the three countries so far. Health-care workers have been particularly hard hit: 521 have been infected, and 272 have died. Data suggest that most of those infections have taken place outside Ebola treatment and care, according to the latest WHO update, which provided no details.

For many weeks now, a truism of the Ebola epidemic is that it moves on “virus time” while the world moves on “bureaucratic time.” A twist on that phenomenon is that the virus is shifty, fading in some places while flaring in others. That challenges global health officials to find a way to be more nimble in their response.

U.S. Army soldiers in recent days have been flying into Liberia by the hundreds to complete the construction of 17 new Ebola Treatment Units. The U.S. military is focused exclusively on Liberia and on carrying out a mission developed by Army planners in Germany in September.

On Wednesday, Aylward said that the empty beds in existing Ebola clinics are “absolutely” needed still and that there are no plans to reduce capacity at this time. He said that it is normal to shuffle resources from one hot zone to another as an epidemic spreads but that it is too soon to let down defenses.

President Obama recognized the work and leadership of U.S. health-care workers in their response to the Ebola threat at the White House on Wednesday. (Ashleigh Joplin/AP)

“These are wily viruses. They are waiting for you to make that kind of mistake,” he said.

The apparent progress overseas comes amid continuing controversy over the treatment of health-care workers who return to the United States from West Africa. Kaci Hickox, a nurse quarantined against her will in recent days, threatened Wednesday to take legal action if Maine does not lift her quarantine by Thursday morning.

“I am not going to sit around and be bullied by politicians and forced to stay in my home when I am not a risk to the American public,” Hickox said on NBC’s “Today” show.

Ebola is spread only through direct contact with the bodily fluids of someone who has symptoms of the disease. Hickox remains free of symptoms, and Ebola tests on Hickox have been negative. But since leaving New Jersey on Monday, she has remained at her home in Maine, where a state trooper has been stationed out front, according to her attorney, Norman Siegel.

“She was a prisoner in a hospital tent [in New Jersey], and now she’s a prisoner in her home in Fort Kent,” he said. “The venue changes, but she’s still quarantined.”

Maine Gov. Paul LePage (R) is looking for ways to force Hickox, who was released from mandatory Ebola isolation in New Jersey, to abide by a 21-day quarantine in Maine, LePage’s office said in a statement. But Siegel said that if Maine officials obtain a required court order to enforce the quarantine, she intends to challenge it.

Doctors Without Borders, the organization with which Hickox worked in Sierra Leone, said in a statement Wednesday that it “strongly disagrees with blanket forced quarantine for health care workers returning from Ebola affected countries.” It added: “Such a measure is not based upon established medical science.”

In Washington, President Obama dismissed critics who have pushed for more aggressive travel restrictions and mandatory quarantines for returning volunteers. Flanked by U.S. medical workers who have either come back from battling the Ebola epidemic in West Africa or will soon head there, Obama said Wednesday that the United States should be treating returning medical personnel like “heroes” rather than stigmatizing them.

“Like our military men and women deploying to West Africa, they do this for no other reason than their own sense of duty, their sense of purpose, their sense of serving a cause greater than themselves,” the president said. “They deserve our gratitude, and they deserve to be treated with dignity and with respect.”

The president was introduced by Kent Brantly, a doctor for the Christian relief group Samaritan’s Purse who became infected with Ebola in Liberia this summer but recovered after being evacuated to Atlanta. Brantly praised the medical personnel from Guinea, Liberia and Sierra Leone who have been battling the epidemic, saying they “have fought with valiant effort against this menace, but they need the help of the international community to turn the tide of this epidemic.”

Obama also warned Wednesday that more infections could surface in the United States, despite efforts to control the virus.

“The truth is that until we stop this outbreak in West Africa, we may continue to see individual cases in America in the weeks and months ahead, because that’s the nature of today’s world,” he said. “We can’t hermetically seal ourselves off. The nature of international travel and movement means that the only way to assure that we are safe is to make sure that we have dealt with the disease where it — right now — it is most acute.”

Ariana Cha and Juliet Eilperin contributed to this report.