Sudan Ebola virus: What do we know?

Uganda declared an outbreak of the deadly Sudan Ebola virus recently, reporting 18 confirmed cases, 18 suspected cases and 23 deaths, according to the World Health Organization (WHO).

The news comes amid global outbreaks of COVID, Zaire Ebola virus and monkeypox — and the Sudan virus shares early characteristics with all of them. What do we know so far about how manifestations of the Sudan Ebola virus differ from those of other global outbreaks?

How is Sudan virus different from Zaire Ebola virus?

Africa saw its most deadly Ebola outbreak between 2014 and 2016, when an Ebola virus from Zaire killed over 10,000 people in Libera, Guinea and Sierra Leone. Since then, scattered outbreaks have cropped up in the Democratic Republic of Congo, where over 2,000 people died of the Zaire Ebola virus between 2018 and 2020.

Though the recent Sudan virus and the 2014 Zaire Ebola strain have different origins, they have similar symptoms including fever, nausea, weakness, loss of appetite and unexplained bleeding.

But WHO experts say there are a few big differences between the two strains, namely: Zaire is deadlier and more transmissible than Sudan Ebola virus.

"The mortality with Ebola Sudan in previous outbreaks was relatively lower than the Ebola Zaire virus," Patrick Otim, a health emergency officer in the WHO Regional Office for Africa's Acute Events Management Unit, said in an online press briefing.

But that doesn't mean Sudan Ebola virus isn't very deadly. According to the WHO, earlier outbreaks have seen mortality rates ranging from 41 to 100%. That's a little lower than Zaire Ebola virus, which has a mortality rate between 60 and 100%, but still alarmingly high.

Along with different mortality rates, some of the physical features vary, too, Otim said.

"Chest pain is not a common symptom in Ebola Zaire. But it is seen in Ebola Sudan," he said.

Like the ongoing COVID-19 and monkeypox outbreaks, the elderly and vulnerable are at greater risk, and chances of surviving the Sudan virus are higher among young people — especially those with sound organ functioning.

Critical cases of the Sudan Ebola virus can endanger kidneys, said William Fischer, director of emerging pathogens at the Institute for Global Health and Infectious Diseases in the US, in a press conference. However, he said, if cases are caught in time, they can be controlled with clinical care.

"Even in cases of organ injury, supportive care can help manage complications," he said. "A common symptom is low blood pressure, which could be dangerous, as it could lead to organ injury, but if caught early, it can be managed."

How does it compare with other viruses?

Immediate symptoms of Sudan Ebola virus infection — like fever and cough — could appear to overlap with the early symptoms of other ongoing outbreaks like COVID, monkeypox and even the flu.

But there are some differences: Characteristic "pocks" and rashes eventually distinguish monkeypox from Ebola virus. And unlike COVID, the Ebola virus is not a respiratory disease. Therefore, symptoms that directly attack the lungs such as cough and shortness of breath remain prominent during COVID-19, while Ebola patients generally progress toward more serious symptoms, such as rashes, vomiting, diarrhea, impaired kidney and liver function and internal bleeding.

How does transmission differ?

Ebola and monkeypox are almost exclusively transmitted by direct contact of bodily fluids from other people or animals, while COVID and the flu are transmitted through the air, making them more contagious.

That's why COVID-19 numbers have soared above 613 million cases since the start of the pandemic in 2020, killing over six million people in under three years, while Ebola — despite being deadlier — has only killed around 15,000 people since it was detected in 1976.

The same goes for flu, which sees up to five million severe cases every year and almost half a million deaths.

Claire Standley, a professor at Georgetown University's Center for Global Health Science and Security, told DW that incubation period is another main difference between COVID and Ebola virus.

While COVID patients can spread the virus even before they start showing symptoms, the Sudan Ebola virus can only be transmitted by people once they're sick, Standley said.

"They are quite ill by that point, and so in that sense it's easier for public health authorities to identify the cases and isolate them," she said.

This "silent transmission" is a main reason why COVID has been able to spread so quickly and cause so many deaths over the past few years.

Monkeypox, which is less transmissible, has seen far fewer cases since the outbreak started this spring. So far, 27 deaths have been recorded.

Why does response vary?

The global response to outbreaks is guided by the virus or disease's transmission potential, virility and fatality.

"Sars-CoV-2 was a new virus, and that was very challenging in terms of response effort," Standley said.

This isn't the case for monkeypox, Ebola and the flu, which experts already know how to treat and tackle.

Standley said that politics also play a role in global response to disease outbreaks.

"There have been endemic cases of monkeypox in central and west Africa for decades, and we have been amid an outbreak in Nigeria for years and the world did not care," she said, referencing the current outbreak of monkeypox in the US and Europe, which has received widespread attention in the media and public health communities.

Response efforts only ramped up when high income countries became affected, she said.

"As soon as cases are reported in the Global North, that's when it started hitting the news and the world mobilized to get vaccine doses out."

Health authorities started rolling out vaccination programs in the US and Europe for people in at-risk groups mere weeks after the first cases of monkeypox were detected.

"But not a single vaccine dose was provided to central or west Africa despite cases there,” said Standley.

Ebola vaccine

There is a vaccine for the Ebola virus, but it caters to the Zaire strain, not the one originating in Sudan.

Health experts maintain that a vaccine dedicated to the Sudan virus is a priority. But to develop a vaccine, researchers need cases to study.

 "It is very important for us to document the clinical efficacy [of vaccines], and for that, you have to have cases, because it occurs in sporadic, rare outbreaks, which is why we are working with the international community to use this opportunity to accumulate data to fill research gaps," said Ana Maria Henao-Restrepo, who works with the WHO to develop blueprints to deal with global epidemics, in a press briefing.