WASHINGTON — The Ebola epidemic in West Africa, already ghastly, could get worse by orders of magnitude, killing hundreds of thousands of people and embedding itself in the human population for years to come, according to two worst-case scenarios from scientists studying the historic outbreak.

The virus could potentially infect 1.4 million people by the end of January, according to a statistical extrapolation by the U.S. Centers for Disease Control and Prevention published Tuesday. That astonishing number came just hours after a report in the New England Journal of Medicine warned that the epidemic might never come fully under control, and that the virus could become endemic in the population, crippling civic life in the affected countries and remaining an ongoing threat to spread elsewhere.

These dire scenarios from highly respected medical sources were framed, however, by optimism from U.S. officials that a ramped-up response can and will contain the outbreak in the weeks and months ahead.

CDC Director Tom Frieden cautioned that the estimates in the new report from his agency do not take into account the actions taken, or planned, since August by the United States and the international community. Help is on the way and it will make a difference, he said – but time is of the essence.

“A surge now can break the back of the epidemic, but delay is extremely costly,” Frieden said.

The situation on the ground in West Africa is bleak, with people dying of Ebola in the streets outside clinics with no available beds, and other victims remaining at home where they are infecting their care-givers. No Ebola outbreak has ever approached the scale of this one. The previous worst outbreak, in Central Africa, involved only 425 infections in Uganda from October 2000 to January 2001, and was brought under control by local responders aided by international organizations, according to the New England Journal of Medicine.

The World Health Organization has reported more than 5,800 cases including more than 2,800 deaths.

The CDC assumed the actual number of cases is 2.5 times higher than what’s officially known.

On graphs showing the rising number of infections and deaths, the lines continue to curve upward. Infections are doubling every 20 days in the coastal nations of Liberia and Sierra Leone, the CDC said. Each infected person is infecting roughly two additional people. The epidemic will begin to subside when that reproduction rate of 2.0 becomes lower than 1.0.

The CDC estimates that in Liberia and Sierra Leone, including unreported cases, there will be about 21,000 total infections by Sept. 30.

The United States recently launched a $750 million effort that includes treatment facilities in Liberia, and the U.N. Security Council voted unanimously last week to create an emergency medical mission to respond to the outbreak. In addition, the WHO is working on moving infected people out of their homes and into small centers that would provide at least rudimentary levels of care, in hopes of increasing survival rates and slowing the transmission of the disease.

Although the United States plans to build 17 treatment centers, each with 100-bed capacity, in Liberia, American personnel will not be staffing those facilities, officials have said. Instead, the U.S. plans to train volunteers and others from aid organizations or nonprofits. Some global health experts have said this could slow down the response because there aren’t enough volunteers stepping forward.