As recoveries rise, doctors are finally learning how Bundibugyo Ebola behaves

As more patients recover from the world's largest recorded Bundibugyo Ebola outbreak, doctors are beginning to piece together how the rare virus behaves - offering the clearest picture yet of one of the disease's least-studied strains.

The number of recoveries reported by Congolese health authorities almost doubled in a week, rising to 148 on Thursday from 80 on June 18, even as treatment centers admit dozens of patients daily.

Previous Bundibugyo outbreaks had lower reported fatality rates than epidemics caused by the more common Zaire and Sudan species, but doctors say it's too early to know whether the current epidemic will follow the same pattern because hundreds of patients remain hospitalized.

The uncertainty reflects how little scientists still know about the virus. Before this year, Bundibugyo had caused just two recognized outbreaks since it was identified in Uganda in 2007, with only 193 confirmed cases combined.

A study published Wednesday in The New England Journal of Medicine, based on the first 505 laboratory-confirmed patients, provides the clearest description yet of the disease. Patients most commonly presented with fever, vomiting, diarrhea, headache, abdominal pain and loss of appetite, while bleeding was uncommon when they first sought care. Researchers also found patients who died carried substantially higher viral loads than survivors.

The current epidemic has already generated six times that number, giving researchers their first real opportunity to determine whether Bundibugyo follows a different clinical course from other Ebola species and how much patient outcomes reflect the biology of the virus versus advances in supportive care.

"There's a feeling that Bundibugyo moves a little more slowly," said Susan McLellan, director of the biocontainment treatment unit at the University of Texas Medical Branch, who cared for Ebola patients in Sierra Leone during the 2014-16 West African epidemic and later in the Democratic Republic of Congo during an outbreak in 2018.

A slower disease course may provide more time to aggressively replace fluids, stabilize blood sugar and electrolyte levels, and administer antiviral drugs before patients become critically ill, she said. But it could also allow infected people to remain in the community longer if early symptoms are mistaken for malaria, cholera or other more common illnesses, delaying diagnosis and giving the virus more opportunity to spread.

The first Ebola patient detected in Uganda sought care at multiple health facilities over more than two weeks with persistent vomiting and diarrhea before the Bundibugyo virus was recognized after his death, researchers reported in Nature Medicine on June 11. The case underscored the importance of integrating private hospitals into Ebola surveillance because they are often the first point of care for patients with severe febrile illness, they said.

Laboratory and animal studies support that hypothesis. In experiments, Bundibugyo multiplied more slowly than the Zaire strain in human cells, and infected ferrets survived several days longer than animals exposed to Zaire Ebola. Researchers caution those findings don't necessarily predict what will happen in patients, where access to early supportive care may be just as important as the biology of the virus itself.

Modern Ebola treatment focuses on rapidly correcting the dehydration, electrolyte disturbances and low blood sugar that develop as patients suffer profuse vomiting and diarrhea, while monitoring for kidney injury and other complications. Those strategies have become increasingly sophisticated since the West African epidemic and are now considered the cornerstone of care.

The next test of whether those advances can further improve survival is expected to begin next week. Researchers plan to launch the first clinical trial of treatments specifically against Bundibugyo Ebola, evaluating whether Gilead Sciences Inc.'s antiviral remdesivir and Mapp Biopharmaceutical Inc.'s monoclonal antibody cocktail MBP134 can reduce deaths from the disease.

Children, however, remain a major concern.

Children and adolescents account for about 15% of confirmed cases, but more than one-quarter of deaths, according to the United Nations Children's Fund. The case-fatality ratio among patients under 18 is almost twice that of adults.

Children aren't thought to be biologically more susceptible to infection, but mild early symptoms may delay recognition, while underlying malnutrition, fragile health systems and the tendency for children to deteriorate rapidly once dehydrated may all contribute to worse outcomes, said Douglas Noble, Unicef's director of public health emergencies.

Previous studies of children hospitalized with Zaire Ebola found they often developed life-threatening electrolyte abnormalities, dangerously low blood sugar and acute kidney injury, underscoring why aggressive supportive care has become a cornerstone of treatment. Researchers also found children carried higher viral loads than adults and took longer to clear the virus, factors associated with poorer outcomes.

While preliminary data suggest the youngest children may be faring worst in the current outbreak, UNICEF said it needs more cases before it can confidently assess outcomes across narrower age groups.

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