The word “Ebola” conjures images of bleeding out of bodily orifices, striking fear in the hearts of many—even with a vaccine available, as one is for the most common strain.
The variant now spreading in Uganda, however, has no approved vaccine.
This week Uganda’s president imposed a three-week lockdown in two districts where cases of Sudan ebolavirus are spreading. Earlier this month, the U.S. Centers for Disease Control and Prevention warned U.S. health care providers to be on the lookout for patients potentially sick with the virus. And the agency began diverting travelers from Uganda to health checks at one of five U.S. airports.
Will the disease make it to the U.S.? No confirmed or suspected cases of Ebola have been reported, the CDC told Fortune on Tuesday. But while experts say the outbreak poses little danger to those outside of Uganda at the moment, “the risk is not zero,” Dr. Maryam Keshtkar Jahromi, an infectious disease doctor and expert on viral hemorrhagic fevers from Johns Hopkins Medicine, said.
Here are some basics on the current Ebola outbreak and the relatively uncommon strain behind it.
When did the outbreak start?
An Ebola outbreak was declared by Ugandan health authorities on Sept. 20 after the case of a patient in Mubende district was confirmed by a laboratory, according to a Sept. 26 World Health Organization update. Since then, the outbreak has infected 58 people, 20 of whom have recovered, Uganda President Yoweri Museveni said this weekend, according to Bloomberg.
There was also a recent outbreak of Ebola in the Democratic Republic of Congo, declared on Aug. 21 following the laboratory confirmation of a fatal case in North Kivu province. No additional confirmed or probable cases were identified, according to the WHO.
Are the two outbreaks related?
No. There are six types of ebolavirus: Zaire, Sudan, Taï Forest, Bundibugyo, Reston, and Bombali. Only the first four are thought to infect humans, according to the CDC. The Zaire strain is the most common and is responsible for most outbreaks, according to the International Society for Infectious Diseases.
The Democratic Republic of Congo case involved the Zaire strain of Ebola, for which there exists a vaccine. The Uganda case involves the Sudan strain, for which no approved vaccine exists.
What is the difference between Sudan and Zaire ebolaviruses?
Symptoms of Ebola are generally the same, regardless of the type of ebolavirus. They include fever, fatigue, muscle pain, headache, and sore throat initially. Vomiting diarrhea, rash, impaired liver or kidney function, and sometimes internal and external bleeding may follow, including oozing blood from the gums and/or bloody stools, according to the WHO.
Can the virus be spread through the air?
“Honestly, no one knows,” Keshtkar Jahromi told Fortune.
While the CDC and WHO state that the virus is transmitted via bodily fluids and not in the air, there’s no proof that’s the case, she says, adding that running such an experiment would be very difficult due to the specialized equipment required.
Does a vaccine exist for Sudan virus?
There is not an approved vaccine, though a vaccine is in the works, Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, told Fortune.
“There is no biological barrier to making a vaccine against Sudan, it just hasn’t been a priority” because the bulk of Ebola cases are caused by Zaire ebolavirus, Adalja said.
While a vaccine—Ervebo—is approved by the U.S. Food and Drug Administration and the WHO for those 18 and older except for pregnant and breastfeeding women, it only protects against Zaire ebolavirus, according to the WHO.
Are treatments available?
Two monoclonal antibody treatments—Inmazeb and Ebanga—are FDA-approved for Ebola in adults and children. They’re only approved for the Zaire strain, however, according to the WHO.
There are a couple of experimental monoclonal antibody treatments being tested for Sudan ebolavirus that are expected to improve symptoms and decrease mortality, Keshtkar Jahromi said.
Treatment is otherwise limited to supportive care, which seeks to alleviate symptoms in patients, and to also provide patients with fluids and electrolytes.
Can an infected person without symptoms spread Ebola?
The incubation period—or time from exposure to when symptoms appear—averages eight to 10 days. But that period can span from two days to 21 days, according to the CDC.
Asymptomatic transmission is possible, Keshtkar Jahromi says. In fact, it’s possible some people have the virus and never experience symptoms.
“If you go to some rural areas of Ebola-endemic countries and take blood specimens from people who don’t remember being infected or having symptoms, you’ll find some people have antibodies against the virus,” she said. “You ask them, ‘Were you ever sick? Were you in contact with someone who was sick? They don’t remember anything. They were infected with the virus sometime and they never had any symptoms.’”
What’s the mortality rate?
Sudan ebolavirus seems to have a lower mortality rate, Keshtkar Jahromi says. While the Zaire ebolavirus tends to have a mortality rate of 60% to 90%, the mortality rate for Sudan ebola virus is thought to be around 40% to 70%, she added.
How likely is the outbreak to spread outside of Uganda?
The question of the hour, no doubt, is “where else may it already have spread, and we don’t know,” Keshtkar Jahromi said.
“There’s always a risk—the risk is not zero,” she said. “But the risk is low with the current situation.”
Adalja called the risk to the U.S. “extremely low” and said that Ebola is “not a very contagious illness.”
“It thrives where exposure to a lot of blood and bodily fluids occur in health care settings, where there is no personal protective equipment,” which generally doesn’t happen in the U.S., he said.
Ebola hasn’t been identified in the U.S. since the 2014–2016 epidemic, during which 11 Americans were treated, according to the CDC. Two died, and the other nine recovered. All had been in West Africa, where an outbreak was occurring, except two health care workers who treated a patient in Dallas, and who contracted the disease but recovered.
While the risk of contracting Sudan ebolavirus outside of Uganda is low right now, people must take the threat seriously, Keshtkar Jahromi says. She recommends that travelers visiting Africa arm themselves with preventative information and not come into contact with wild animals, because they could contract the virus by doing so.
If you’re symptomatic at the border, “be proactive and just tell them, ‘This is what I’m experiencing, this is where I have been. I need help, and I’m helping my community.’”
