The Centers for Disease Control and Prevention on Thursday asked U.S. physicians to watch for cases of Ebola, which has been surging in Uganda in recent weeks.
As of Thursday, there were 44 confirmed cases and 10 deaths in Uganda, with a few dozen possible cases and 20 deaths still under investigation, making this the largest outbreak in that country in 20 years. At least six infections and four deaths occurred among health care workers.
No cases have yet been reported outside Uganda, and American doctors are being alerted as a precaution, according to the agency’s alert. There are no approved drugs or treatments for the type of Ebola virus causing the outbreak in Uganda.
The agency urged physicians to obtain a travel history from patients whom they suspect of having Ebola.
“While there are no direct flights from Uganda to the United States, travelers from or passing through affected areas in Uganda can enter the United States on flights connecting from other countries,” the C.D.C. alert said.
Ebola is a rare and deadly disease, seen mostly in sub-Saharan Africa. The infection begins with mild respiratory symptoms, but left untreated can rapidly damage internal organs.
Patients eventually bleed from their eyes, nose, mouth and rectum — dramatic symptoms that have stoked fear of the virus. Ebola kills about half of those infected on average, usually within two weeks of the appearance of symptoms.
The C.D.C. and the World Health Organization both provide information on how to diagnose and treat patients infected with the virus.
The outbreak was first detected in Mubende, Uganda, but has already spread to four other districts in a 75-mile radius. There will be many more cases and deaths before the virus can be contained, said Dr. Fiona Braka, emergency operations manager at the W.H.O. regional office for Africa, based in Brazzaville.
“We are concerned because we still haven’t reached the peak,” Dr. Braka said.
The virus was circulating undetected for some time, and even after the first patient was diagnosed, health officials have been able to trace only three-quarters of the people who may have been exposed, Dr. Braka said.
The remaining contacts have scattered, raising the possibility that cases will sprout in other parts of the country or the world.
Ebola is highly contagious, and previous outbreaks have quickly spiraled out of control. The largest tore through West Africa in 2014 and accounted for more cases than all previous ones combined. By its end, the W.H.O. reported 28,616 cases and 11,310 deaths.
The toll included 11 Americans, nine of whom contracted the disease outside the United States. Two of them died.
The World Health Organization has twice declared a public health emergency of international concern — the organization’s highest alert — for Ebola: in 2014, and again in 2019, when the virus surfaced in the Democratic Republic of the Congo.
The vaccines and treatments approved for Ebola target the Zaire species, the primary source of previous outbreaks. But they are ineffective against the Sudan species now circulating in Uganda.
Anticipating that vaccines against the Sudan species might someday be necessary, scientists have been working on at least eight candidates.
The furthest in development is a single-dose vaccine developed by the Vaccine Research Center at the National Institutes of Health, which has been licensed to the Sabin Vaccine Institute.
The vaccine has been shown to be safe, produces copious antibodies against the virus, and is highly protective against the Sudan virus in monkeys. About 100 doses are readily available.
Another vaccine candidate, made by a British team, targets both Zaire and Sudan species, but is in early-stage trials. Only 81 doses are available.
Both candidates could be made available in clinical trials during the current outbreak, pending approval from Ugandan health authorities.
Sabin also has enough bulk material to produce 40,000 doses of its vaccine, stored at a biotech company called ReiThera, in Italy. But filling and finishing those doses in vials will take at least until the end of the year, according to Dr. Rick Koup, acting director of the federal vaccine center.
Health officials came up against similar hurdles in acquiring doses of the monkeypox vaccine, which hindered the response in the initial weeks of the U.S. outbreak. That vaccine is still in short supply worldwide.
“These are two rapid succession cases where clearly we need to come up with a better solution,” Dr. Koup said.
Few facilities can fill and finish vaccines, creating a bottleneck when doses are urgently needed. On the other hand, finished doses expire more quickly, requiring emergency stocks to be constantly replenished.
Two months ago, Dr. Koup said, he would have predicted that finishing doses of a suddenly needed vaccine was “not going to be a big issue.” But in hindsight, he said, “obviously, we should have had a few thousand doses filled.”
Activists lauded federal scientists for having the foresight to develop vaccines for emerging pathogens. But instead of relying on private companies, the government should own and control a vaccine manufacturing facility that can be used during an outbreak, said James Krellenstein, a founder of PrEP4All, a group that promotes access to H.I.V. care.
“How many outbreaks do we have to watch spiral out of control because of the lack of vaccine manufacturing capacity before the U.S. government fixes this problem?” Mr. Krellenstein said. “The thing that’s very frustrating is, this is really a fixable problem.”
Scientists have also been developing so-called monoclonal antibodies that can broadly neutralize multiple species of Ebola and reverse symptoms. One dose of an antibody cocktail has been shown to ease even severe symptoms in monkeys infected with the Zaire, Sudan and Bundibugyo species of Ebola. But the treatment is still in early-stage trials.
“If you go fishing for these rare rainbow unicorn antibodies, you can certainly find ones that are cross-neutralizing and cross-protective” against various types of Ebola, said Kartik Chandran, a virologist at the Albert Einstein College of Medicine in New York who helped develop the treatment.
“We knew it was only a matter of time before we had another Ebola outbreak that wasn’t caused by Zaire,” he added.
In Uganda, officials have moved quickly to scale up the response to the unexpected outbreak. Contact-tracing continues to increase, and about 950 village health officials in the affected districts have been trained to watch for symptoms. They have been given personal protective equipment, thermometers and beds, Dr. Braka said.
Learning from previous outbreaks, officials moved testing from the Uganda Virus Research Institute in Entebbe to a mobile lab in Mubende, the outbreak’s epicenter, she added. Confirmation of the diagnosis now takes just six hours.